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Binary star

A binary star, also known as a binary star system, is a gravitationally bound pair of stars that orbit their common center of mass, following Kepler's laws of planetary motion adapted for two bodies.^[1] These systems are the most common form of multiple star configurations in the Milky Way galaxy, with over half of all stars belonging to binary or higher-order multiple systems.^[1] Binary stars are classified based on observational methods: visual binaries are those where the individual stars can be resolved and their orbital motion tracked directly through telescopes; spectroscopic binaries are detected via periodic Doppler shifts in their spectral lines indicating orbital velocities; eclipsing binaries exhibit periodic dips in brightness when one star passes in front of the other from Earth's viewpoint; and astrometric binaries are inferred from the wobble in a star's position against background stars.^[2] The orbital periods of binaries range from hours to millions of years, with separations varying from contact binaries—where the stars share a common envelope—to widely separated pairs orbiting at distances comparable to our solar system.^[1] These systems are crucial for astronomy because they provide the primary means to determine stellar masses, radii, and densities through analysis of their orbits and light curves, offering insights into stellar evolution, the initial mass function, and even the production of heavy elements via mergers.^[2] In close binaries, mass transfer between stars can lead to phenomena such as novae, Type Ia supernovae, or X-ray emissions when one component is a compact object like a white dwarf, neutron star, or black hole.^[3] Additionally, some binary systems host planets, influencing habitability considerations in exoplanet studies.^[1]

History and Nomenclature

Historical Discovery

The recognition of binary stars began in the late 18th century with systematic observations of double stars, initially presumed to be mere optical alignments along the line of sight. In 1781, British astronomer William Herschel cataloged Castor (α Geminorum) as a prominent double star during his sweeps of the night sky using a self-built reflector telescope, marking one of the earliest documented instances of such a pair in modern astronomy. Herschel's extensive surveys from 1781 to 1802 revealed relative motions among several doubles, leading him to propose in 1802 that some, including Castor, were physical systems orbiting a common center of gravity rather than coincidental projections, thus founding the study of binary star dynamics. A pivotal advancement came through astrometric observations in the 19th century, demonstrating unseen companions via perturbations in visible stars' paths. In 1844, German astronomer Friedrich Wilhelm Bessel analyzed the proper motion of Sirius (α Canis Majoris) and detected a periodic wobble indicative of an orbiting dark companion with an approximately 50-year period, predicting its existence despite its invisibility to contemporary telescopes.^[4] This unseen partner, Sirius B, was visually confirmed on January 31, 1862, by American astronomer Alvan Graham Clark during testing of a new 18.5-inch refractor at his father's observatory in Cambridgeport, Massachusetts, revealing a faint white dwarf and validating Bessel's foresight.^[5] Such detections underscored binaries' role in probing stellar masses through orbital mechanics. The late 19th century introduced spectroscopic methods to uncover invisible binaries via radial velocity variations. In 1782, young English astronomer John Goodricke noted the periodic dimming of Algol (β Persei) every 2.87 days, attributing it to an eclipsing companion rather than intrinsic pulsation, though the mechanism was not fully understood until later.^[6] The advent of astronomical photography after 1880 enabled precise light curve measurements for eclipsing systems like Algol, while in 1889, German spectroscopist Hermann Carl Vogel at Potsdam Observatory detected alternating Doppler shifts in Algol's spectral lines, confirming its binary nature as the first spectroscopic binary and linking variability to orbital motion.^[7] Advancing into the early 20th century, astronomers refined classifications to better interpret binary spectra and orbits. In the 1890s, American astronomer Antonia Maury at Harvard College Observatory developed a detailed spectral classification system from photographic plates, identifying subtle line-width variations that distinguished spectroscopic binaries like β Aurigae (discovered by her in 1890 as the second such system) and Mizar, where she determined the first orbital period for a spectroscopic pair.^[8] Concurrently, Henry Norris Russell at Princeton advanced binary analysis through statistical methods for deriving masses and distances from orbital elements, particularly through his 1912 studies on eclipsing binaries in collaboration with Harlow Shapley, which established methods for deriving stellar masses and radii from light curves, foundational for understanding stellar evolution.^[9]^[10]

Etymology and Designations

The term "binary star" derives from the Latin word binarius, meaning "two together" or "consisting of two," reflecting the paired nature of these stellar systems. It was first introduced in English astronomical literature by Sir William Herschel in his 1802 paper "On the Construction of the Heavens," where he used it to describe gravitationally bound pairs of stars orbiting a common center of mass, distinguishing them from mere optical doubles. In binary star systems, components are designated as primary (A) and secondary (B), typically based on relative brightness, with the brighter or more massive star labeled A; if brightness is similar, discovery order may determine the assignment. For hierarchical multiple systems, subsystems receive suffixes such as Aa and Ab for close pairs within the primary, or Ba and Bb for those around the secondary, ensuring a structured notation that reflects orbital hierarchies. Discoverer notations often append letters like AB to catalog entries (e.g., HD 12345 AB) to indicate resolved components.^[11] When temperature differences are significant, the secondary may be labeled as the "hot companion" or "cool companion" relative to the primary, a convention commonly applied in systems involving white dwarfs or hot subdwarfs paired with cooler giants. For instance, in binaries with a white dwarf secondary, it is frequently termed the hot companion due to its elevated surface temperature compared to the primary. The International Astronomical Union (IAU) establishes standards for these designations in multiple systems to maintain consistency and avoid conflicts with variable star nomenclature, which uses sequences like R–Z, RR–RZ, and V-numbering (e.g., V 335 Cygni); Bayer or Flamsteed letters for binaries are preserved without reassignment to prevent overlap.^[11]

Fundamentals and Characteristics

Definition and Basic Properties

A binary star, or binary star system, consists of two stars that are gravitationally bound to each other and orbit around their common center of mass, bound by mutual gravitational attraction. This distinguishes true binaries from optical doubles, which are pairs of unrelated stars that appear close together from Earth's perspective due to chance alignment along the line of sight but are not physically interacting.^[12]^[3] The orbital motion arises directly from the gravitational influence between the two stars, with the center of mass located closer to the more massive star, dividing the separation in the inverse ratio of their masses. Binary stars exhibit a wide range of basic properties shaped by their gravitational interaction. Separations between the stars vary dramatically, from extremely close systems where the stars nearly touch or share outer gaseous envelopes (contact binaries), to wide binaries separated by thousands of astronomical units or even up to about 1 light-year while remaining bound. The mutual gravity influences their evolution, particularly in closer systems where tidal forces can synchronize rotations or drive mass transfer, though wide binaries evolve largely independently like isolated stars. Approximately half of all stars in the Milky Way belong to binary or higher-multiplicity systems, with the fraction reaching about 57% for solar-type (G-dwarf) stars in the solar neighborhood.^[13]^[14] Key parameters defining a binary system's properties include the orbital separation (often expressed as the semi-major axis), the eccentricity (which quantifies the orbital shape from circular at 0 to highly elliptical approaching 1), and the inclination (the angle between the orbital plane and the plane of the sky, ranging from 0° for face-on to 90° for edge-on views). These parameters determine observable effects and the system's dynamical behavior. Unlike single stars, whose masses can only be inferred indirectly, binaries enable precise mass determinations for both components through application of Kepler's third law to their orbital periods and separations, providing essential benchmarks for stellar evolution models.^[15]^[16]

System Configurations

Binary star systems are classified into configurations based on the relative positions and interactions between their components, primarily determined by how closely the stars approach their Roche lobes—the teardrop-shaped regions around each star where its gravity dominates. These configurations range from widely separated pairs with minimal interaction to tightly bound systems where the stars share material or envelopes. The primary categories are detached, semi-detached, and contact binaries, as established in foundational work on close binary dynamics.^[17]^[18] Detached binaries consist of two stars separated by distances greater than their Roche lobes, preventing any significant mass transfer or tidal distortion beyond orbital motion. In these systems, each star evolves largely independently, as the separation exceeds the sum of their radii, typically on scales from several astronomical units (AU) downward to just beyond contact thresholds. For instance, visual binaries like Sirius A and B exemplify detached configurations, with separations around 20 AU allowing isolated evolution despite gravitational binding. No material exchange occurs, preserving the individual stellar envelopes.^[19]^[20] Semi-detached binaries feature one star filling its Roche lobe while the other remains within its own, leading to mass transfer from the lobe-filling (donor) star to the companion via Roche lobe overflow. This configuration often arises in systems where the donor is a more evolved star, such as a giant, transferring material through the inner Lagrangian point, which can form accretion disks around the recipient. Classic examples include Algol-type systems, where the less massive but more evolved component donates hydrogen-rich material, altering the system's mass ratio over time. The transferred mass fuels phenomena like X-ray emission from accretion but does not result in full envelope sharing.^[18] Contact binaries, the closest configurations, involve both stars overfilling their Roche lobes and sharing a common envelope of gas, with their surfaces in direct physical contact. These systems exhibit continuous mass exchange and distorted shapes due to tidal forces, often appearing as a single, ellipsoidal object from afar. A prominent subtype is the W Ursae Majoris (W UMa) variables, late-type main-sequence stars (spectral types F, G, or K) with orbital periods of 0.2 to 1 day and separations on the order of 10-20 solar radii, where the cooler, larger component transfers mass to the hotter one, equalizing temperatures across the envelope. W UMa systems, named after the prototype with a period of about 0.4 days, are characterized by shallow, symmetric light curves from their overcontact nature.^[21]^[18] Binary configurations also distinguish between wide and close systems based on separation scales, which influence interaction strength and evolutionary paths. Wide binaries have separations exceeding several hundred AU—up to 10,000 AU or more—resulting in weak tidal effects and evolution akin to single stars, as seen in systems like Zeta Reticuli with a separation of about 3,700 AU.^[22] In contrast, close binaries occupy smaller scales, from tens of solar radii to a few AU, enabling significant interactions like those in the configurations above; for example, periods under 100 days correspond to separations below 1 AU, fostering mass transfer or synchronization. These distinctions highlight how separation governs whether binaries behave as isolated pairs or interactive units.^[23]^[24]

Classification by Observation

Visual Binaries

Visual binaries are binary star systems in which the individual stellar components can be spatially resolved as distinct points of light through telescopic observations, enabling astronomers to track their relative motions directly over time.^[25] This resolution distinguishes them from other binary types, as it relies on angular separation rather than indirect effects like light variations or spectral shifts.^[16] Such systems typically exhibit separations large enough to overcome atmospheric seeing limitations from the ground, often exceeding a few arcseconds for amateur telescopes, though professional instruments can resolve much closer pairs.^[26] Observing visual binaries demands high angular resolution to discern the components, particularly for systems with small separations like that of Sirius A and B, where the angular distance varies between 3 and 11 arcseconds over their 50-year orbital period.^[27] Ground-based telescopes historically required clear skies and stable seeing conditions, but even then, faint or closely paired secondaries posed challenges; for instance, Sirius B, a white dwarf companion 10,000 times fainter than Sirius A, was not resolved until 1862 by Alvan Clark using a 18.5-inch refractor.^[28] The primary advantage of visual binaries lies in the direct determination of key orbital parameters, such as the semi-major axis in arcseconds (denoted as α″), inclination, and position angle, which can be plotted to construct the relative orbit without needing distance estimates initially.^[29] Historically, the distinction between true physical binaries and optical alignments—pairs appearing close due to chance projection along the line of sight—emerged through early telescopic studies, exemplified by the Big Dipper's Mizar and Alcor.^[30] While Alcor and Mizar appear as a naked-eye double (separation ~12 arcminutes), telescopic examination in 1650 by Giovanni Battista Riccioli revealed Mizar itself as a closer visual binary with its companion (now Mizar B), separation ~14 arcseconds, marking one of the first confirmed orbiting pairs and highlighting the need to differentiate bound systems from unrelated projections via proper motion tracking.^[31] This discovery underscored the prevalence of multiples, as Mizar A later proved to be an eclipsing binary itself.^[32] Modern observations of visual binaries benefit from space-based telescopes that eliminate atmospheric distortion. The Hubble Space Telescope (HST), with its ~0.05 arcsecond resolution, has resolved tight pairs in dense regions like the Orion Nebula Cluster, identifying over 100 visual binaries among young stars and enabling orbit fitting for multiplicity studies.^[33] Similarly, the Gaia mission provides exquisite proper motion data (precisions down to microarcseconds per year) for millions of stars, facilitating the identification and orbital characterization of wide visual binaries up to separations of tens of arcseconds, while confirming physical associations through common space motions.^[34] These tools have revolutionized the field by expanding catalogs from historical samples of a few thousand to systematic surveys encompassing hundreds of thousands of systems.^[35]

Spectroscopic Binaries

Spectroscopic binaries are binary star systems in which the individual components cannot be spatially resolved but are identified through periodic variations in their radial velocities, as revealed by Doppler shifts in the wavelengths of their spectral lines. These shifts occur because the stars orbit their common center of mass, alternately approaching and receding from the observer, causing absorption or emission lines to blueshift and redshift periodically.^[36] This method is particularly effective for detecting close binaries with short orbital periods, where the orbital speeds produce measurable velocity changes of tens to hundreds of km/s. In single-lined spectroscopic binaries (SB1), the spectral lines of only one component—usually the brighter, hotter, or more massive star—are visible and vary periodically, allowing determination of that star's orbital velocity amplitude but implying the companion's mass only through the mass function.^[37] This configuration often arises when the secondary star is much fainter or cooler, making its lines undetectable against the primary's spectrum.^[38] In contrast, double-lined spectroscopic binaries (SB2) show distinct sets of lines from both stars, each shifting with their respective orbital motions, which permits measurement of the velocity ratio and thus the mass ratio directly.^[39] The radial velocity curve for a spectroscopic binary traces the periodic velocity variation, typically sinusoidal for circular orbits, with the semi-amplitude K providing key orbital insight via the relation

K = \left( \frac{2\pi G}{P} \right)^{1/3} \frac{M_2 \sin i}{(M_1 + M_2)^{2/3}}

for the observed star in a circular orbit (e=0), where M_1 and M_2 are the masses of the observed star and companion, P is the orbital period, i is the inclination, and G is the gravitational constant.^[36] Fitting this curve to observed line shifts yields the period and amplitude, though the unknown inclination limits absolute masses to a lower bound from the mass function. Spectroscopic binaries dominate among short-period systems, comprising a significant fraction of close stellar pairs; for instance, at least 20% of extreme Population II stars exhibit spectroscopic binaries with periods under 2000 days.^[40] A classic example is Algol (β Persei), an SB1 system where only the primary B8V star's lines are clearly observed, revealing its orbital motion around an unseen K2IV companion.^[41]

Eclipsing Binaries

Eclipsing binaries are binary star systems in which the orbital plane is oriented nearly edge-on relative to the observer's line of sight, with an inclination close to 90 degrees, allowing one star to periodically pass in front of the other and occult its light.^[42] This alignment results in observable periodic decreases in the system's apparent brightness, known as eclipses, which occur twice per orbital cycle: once when the foreground star eclipses the background one (transit) and once in the reverse (occultation).^[43] The phenomenon was first rigorously analyzed by Henry Norris Russell in his seminal 1912 papers, which established methods for deriving orbital elements from light curves.^[44] The light curve of an eclipsing binary, which plots the system's brightness against time, exhibits characteristic minima corresponding to the eclipses. The primary minimum is the deeper dip, typically occurring when the hotter, more luminous star is eclipsed by its cooler companion, while the secondary minimum is shallower and arises when the cooler star is eclipsed.^[45] The duration and depth of these minima depend on the relative sizes of the stars and the inclination of the orbit; for instance, the depth ratio between primary and secondary minima reflects the surface brightness ratio, which is influenced by the stars' temperatures and radii.^[46] Modeling these light curves, often using tools like the ellc code, allows for the extraction of precise geometric parameters such as the fractional radii (stellar radii relative to the semi-major axis).^[47] Eclipses in binary stars are classified as total, annular, or partial based on the degree of overlap between the stellar disks. In a total eclipse, the eclipsing star completely covers the eclipsed one, leading to a flat-bottomed minimum in the light curve if the stars are uniform in brightness.^[48] An annular eclipse occurs when the eclipsing star is smaller than the eclipsed one, resulting in a ring-like exposure of the background star's limb during mid-eclipse. Partial eclipses involve incomplete overlap throughout the event, producing V-shaped or rounded minima. Additionally, eclipses can be grazing, where the stars barely touch at their edges, yielding shallow dips, or deep, involving substantial overlap for more pronounced brightness changes.^[49] The primary utility of eclipsing binaries lies in their ability to provide direct measurements of fundamental stellar properties, including radii and effective temperatures, which are otherwise challenging to obtain for individual stars. By combining light curve analysis with spectroscopic radial velocity data to measure orbital speeds, the absolute masses and thus densities of the components can also be determined, offering benchmarks for stellar evolution models.^[50] A classic example is Algol (Beta Persei), an eclipsing binary with an orbital period of 2.867 days, where light curve modeling has revealed the primary star's radius as approximately 2.8 solar radii and surface temperature around 13,000 K, while the secondary is cooler at about 4,500 K with a radius of 3.5 solar radii.^[51] These systems are particularly valuable for testing theoretical relations like the mass-luminosity and mass-radius dependencies in low-mass stars.^[52] Photometric variability in binaries can also arise without full eclipses through effects like ellipsoidal distortion, where the stars' tidal deformation causes brightness modulation due to varying projected areas, or reflection, where the secondary star illuminates the primary's facing side; however, these produce shallower, non-eclipsing light curves that require higher precision to detect.^[43]

Astrometric Binaries

Astrometric binaries are unresolved binary star systems where the companion star is not directly visible, but its presence is inferred from the periodic perturbations in the proper motion of the primary star as it orbits the common center of mass. These perturbations manifest as a measurable wobble in the position of the photocenter—the apparent center of light—over time, detectable through high-precision astrometric observations.^[53]^[35] Detecting astrometric binaries requires long-term monitoring of stellar positions with sub-milliarcsecond accuracy to track deviations from linear proper motion. The key observable is the semi-major axis α of the photocenter's orbital ellipse, expressed in arcseconds, which quantifies the angular extent of the wobble relative to the system's distance. Ground-based observatories and space missions like Hipparcos have historically provided such data, but modern surveys emphasize continuous tracking to resolve orbital curvature.^[54]^[35] The utility of astrometric binaries lies in their ability to yield dynamical masses when combined with parallax measurements, enabling estimates of the total system mass via Kepler's third law adapted for angular parameters. For instance, Proxima Centauri was identified as an astrometric companion to the Alpha Centauri AB binary system, with an orbital period of approximately 550,000 years, semi-major axis of about 8,700 AU, and eccentricity of 0.5, confirming its gravitational binding through analysis of historical astrometric datasets including Hipparcos intermediate astrometry. This approach has revealed wide-orbit companions that would otherwise remain undetected.^[55]^[56] However, astrometric detection is limited to systems with sufficiently long orbital periods, typically ranging from years to centuries, as shorter periods demand even higher temporal resolution to capture multiple orbital phases. These extended timescales often necessitate decades of baseline data, restricting earlier discoveries to nearby, bright stars. The European Space Agency's Gaia mission has dramatically improved prospects by providing microarcsecond-precision astrometry for billions of stars, enabling the identification of millions of astrometric binaries with periods between 0.03 and 30 years, particularly within 250 parsecs.^[35]^[57] Unlike visual binaries, where both components can be spatially resolved, astrometric binaries rely solely on the unresolved positional perturbations, making them particularly effective for inferring dark or low-luminosity companions similar to those detected via spectroscopic methods.^[35]

Orbital Dynamics

Orbital Periods and Variations

The orbital periods of binary star systems span an extraordinarily wide range, from as short as a few hours in contact binaries—such as those in the W Ursae Majoris class, where the stars share a common envelope—to several million years in widely separated pairs that orbit at distances comparable to those in our outer solar system.^[58]^[59] This diversity reflects the varied formation histories and separations of these systems, with the majority exhibiting periods between approximately one-third of a year and 300,000 years.^[58] Typical or median periods cluster around 10 to 100 years, depending on the observational sample, allowing for a broad spectrum of dynamical behaviors from rapid interactions to near-isolated evolution.^[58] The relationship between a binary system's orbital period P and its semi-major axis a is governed by an adaptation of Kepler's third law, derived from Newtonian gravity for two orbiting masses. For a binary pair, the law takes the form P^2 \propto \frac{a^3}{M_1 + M_2}, where M_1 and M_2 are the masses of the component stars in solar units, a is in astronomical units, and P is in years; more precisely, P^2 = \frac{4\pi^2}{G(M_1 + M_2)} a^3.^[15] This formulation enables astronomers to infer total system mass from measured periods and separations, highlighting how more massive binaries tend to have shorter periods for a given separation compared to single-star planetary orbits.^[15] While many binary orbits approximate Keplerian stability, deviations arise from various physical processes that introduce aperiodic or secular variations in the orbital period. Mass transfer between components, particularly in close systems where one star evolves faster, can alter the period by redistributing angular momentum, often leading to expansion or contraction of the orbit. Tidal friction, caused by gravitational distortions raising tides on the stars, dissipates energy and circularizes orbits while gradually changing the period through synchronization of rotational and orbital motions.^[60] Perturbations from a third body, such as a distant companion or circumbinary material, can induce non-Keplerian effects like apsidal precession or eccentricity oscillations, further modulating the observed period.^[60] Secular effects, which accumulate over long timescales, manifest as gradual increases or decreases in the orbital period, often on the order of 1-10% over decades in close binaries monitored via timing data.^[61] These changes are typically attributed to conservative or non-conservative mass transfer and angular momentum loss mechanisms, with observations showing, for instance, period decreases in systems like TV Cassiopeiae due to mass accretion onto the secondary.^[61] In wider systems, such variations are subtler and dominated by external perturbations, but they underscore the dynamic nature of binary evolution. Orbital periods are primarily measured through indirect observational techniques tailored to the system's geometry. For eclipsing binaries, where the inclination allows periodic occultations, the period is determined from the recurrence interval of light curve minima, providing precise values down to minutes for short-period systems.^[62] In spectroscopic binaries, the period emerges from the cyclic Doppler shifts in radial velocity curves, derived from spectral line displacements over multiple observation cycles, which is particularly effective for unresolved or non-eclipsing pairs.^[36] Combining these methods with astrometric data enhances accuracy, revealing periods that might otherwise remain undetected.

Center of Mass Calculations

In binary star systems, the center of mass, also known as the barycenter, serves as the common balance point around which both stars orbit, satisfying the condition M_1 r_1 = M_2 r_2, where M_1 and M_2 are the masses of the two stars, and r_1 and r_2 are their respective distances from the center of mass.^[63] This equilibrium ensures that the system's total angular momentum is conserved, with the more massive star orbiting at a smaller radius. The position vector of the center of mass is given by

\mathbf{r}_{\rm cm} = \frac{M_1 \mathbf{r}_1 + M_2 \mathbf{r}_2}{M_1 + M_2},

where \mathbf{r}_1 and \mathbf{r}_2 are the position vectors of the stars relative to an arbitrary origin.^[64] Observational data on orbital velocities further reveal that the ratio of the stars' orbital speeds satisfies v_1 / v_2 = M_2 / M_1, as the linear speeds are inversely proportional to the masses due to the fixed orbital period.^[65] For spectroscopic binaries, the mass ratio q = M_2 / M_1 (assuming M_1 > M_2) can be directly determined from radial velocity measurements, where the semi-amplitudes K_1 and K_2 of the Doppler shifts yield K_1 / K_2 = q, since the projected orbital speeds scale with the inverse mass ratio and the inclination angle i cancels out in the ratio.^[66] This relation holds for double-lined spectroscopic binaries where spectra of both components are resolved, allowing precise K values to be extracted. The relative orbit of the two stars, as viewed from the center-of-mass frame, traces an ellipse with semi-major axis a = a_1 + a_2, where a_1 and a_2 are the individual semi-major axes; this relative motion simplifies the two-body problem to an equivalent one-body problem using the reduced mass \mu = \frac{M_1 M_2}{M_1 + M_2}, which orbits the total mass M = M_1 + M_2 at separation a.^[65] In this framework, the stars' paths appear as similar ellipses scaled by their mass ratios, with the primary star's orbit enclosing the secondary's in a 1:q area ratio. A key application of center-of-mass dynamics is the determination of the total mass in visual binaries, where the angular separation and proper motion allow measurement of the semi-major axis a (in AU) and orbital period P (in years). Applying Newton's generalization of Kepler's third law to the reduced-mass system, the gravitational force provides the centripetal acceleration for the relative orbit: \frac{G M_1 M_2}{a^2} = \mu \frac{4\pi^2 a}{P^2}, where the right side derives from the orbital speed v_{\rm rel} = \frac{2\pi a}{P} and acceleration v_{\rm rel}^2 / a. Substituting \mu = \frac{M_1 M_2}{M} and simplifying yields M = M_1 + M_2 = \frac{4\pi^2 a^3}{G P^2}, with G ensuring units consistency (in solar masses when a is in AU and P in years).^[15] This formula, first applied systematically in the 19th century, enables mass estimates for hundreds of visual pairs, such as Alpha Centauri A and B, where a \approx 23.5 AU and P \approx 79.9 years give M \approx 1.10 + 0.92 = 2.0 \, M_\odot.^[67]

Formation and Evolution

Formation Mechanisms

Binary stars primarily form through the fragmentation of collapsing molecular cloud cores during the early stages of star formation. In this process, a dense core within a molecular cloud undergoes gravitational collapse, leading to the formation of two or more protostellar disks that accrete material and evolve into companion stars. Fragmentation of molecular cloud cores and protostellar disks is considered the primary mechanism for binary formation, with dynamical capture playing a supplementary role in dense environments. This mechanism is supported by hydrodynamic simulations showing that turbulent molecular clouds naturally fragment into multiple substructures, with core fragmentation producing binaries at separations of hundreds to thousands of AU.^[68] Observations of young stellar regions, such as those in the Perseus molecular cloud, confirm that many protostellar systems emerge from such fragmented cores, often resulting in wide binaries.^[69] A related process involves disk instability, where turbulence or gravitational instabilities in the protostellar disk around a forming star lead to the collapse of dense clumps, enabling paired accretion and the birth of a companion. This occurs in massive, self-gravitating disks where the Toomre parameter Q < 1, allowing gravitational collapse to form secondary protostars at closer separations, typically below 100 AU. Simulations demonstrate that such instabilities are triggered by the rapid infall of material from the parent core, promoting the formation of close binaries through localized fragmentation.^[68] This pathway complements core fragmentation by explaining the prevalence of tighter orbits observed in spectroscopic binaries. An alternative mechanism is the dynamical capture hypothesis, where two independent protostars in a dense star-forming region gravitationally interact and become bound through three-body encounters or gas-assisted friction. In young clusters, this process is enhanced by the high stellar density, allowing for efficient capture of companions, particularly for wider binaries. Recent models suggest that gas dynamical friction in star-forming regions can facilitate capture, contributing to a fraction of observed binaries, particularly in dense clusters.^[70] Initial conditions in young clusters favor high multiplicity, with simulations and observations showing that nearly all stars form in binary or multiple systems, though the efficiency for stable binaries stabilizes at 30-50% as dynamical interactions disrupt some pairs. This fraction is evident in clusters like NGC 1818, where the binary population reflects the turbulent environment of formation.^[71] Recent 2025 studies highlight how circumbinary disks around young binaries influence orbital alignment and migration, with misaligned disks leading to polar configurations that stabilize the system during early evolution. These findings, from observations of brown dwarf binaries, suggest that disk-star interactions play a key role in shaping the final binary architecture.^[72]

Mass Transfer and Common Envelope Evolution

In binary star systems, mass transfer typically begins when the more evolved star expands during its post-main-sequence phase and fills its Roche lobe, the teardrop-shaped region of space surrounding each star defined by the inner Lagrange point where gravitational forces balance. This Roche lobe overflow (RLOF) allows material from the donor star to flow through the L1 point toward the companion, driven by the donor's pressure gradient exceeding the Roche potential. The process alters the binary's orbital dynamics, as the transferred mass carries angular momentum, potentially widening or shrinking the orbit depending on the mass ratio and angular momentum loss. The stability of mass transfer hinges on the donor's response to mass loss compared to the Roche lobe's adjustment. Stable transfer occurs when the donor shrinks faster than or at the same rate as the Roche lobe, allowing gradual material exchange on the donor's thermal timescale, often conserving total mass if the accretor captures most of it (conservative transfer). In contrast, unstable transfer arises when the donor expands more than the Roche lobe contracts, leading to runaway mass loss on a dynamical timescale and typically non-conservative outcomes where excess material is ejected from the system. Stability criteria depend on the donor's structure: convective-envelope donors (e.g., red giants) often experience stable transfer for mass ratios q = M_donor/M_accretor ≲ 2, while radiative-envelope donors (e.g., main-sequence or shell-burning stars) are prone to instability even at lower q. Unstable mass transfer frequently initiates a common envelope (CE) phase, where the donor's envelope engulfs the companion, causing rapid orbital inspiral due to drag forces. During CE evolution, the companion's orbit decays as its kinetic energy and angular momentum are deposited into the envelope, potentially ejecting it if sufficient orbital energy is available.^[73] The envelope's binding energy is approximated by

E_\mathrm{bind} = -\frac{G M_\mathrm{env} M_\mathrm{core}}{\lambda R_\mathrm{env}},

where M_\mathrm{env} and R_\mathrm{env} are the envelope mass and radius, M_\mathrm{core} is the core mass, G is the gravitational constant, and \lambda (typically 0.01–1) accounts for internal energy contributions and structure.^[73] Ejection efficiency is parameterized by \alpha, where the change in orbital energy \Delta E_\mathrm{orb} = \alpha (E_\mathrm{bind}), with \alpha \approx 1 for full efficiency. Successful CE ejection results in a tighter post-CE orbit, often forming short-period systems like cataclysmic variables or double white dwarfs, while insufficient energy leads to merger. These tight binaries are key progenitors for Type Ia supernovae via subsequent mass transfer reigniting carbon fusion.^[73] Mass transfer episodes, whether stable or leading to CE, typically span $10^4–$10^6 years, governed by the donor's thermal adjustment timescale during giant-branch evolution.^[74]

End States and Runaways

Binary star systems reach their end states through a variety of explosive and dynamical processes, often triggered by the evolution of their components into compact objects like white dwarfs, neutron stars, or black holes. These terminal phases can result in dramatic outbursts, stellar ejections, or mergers, leaving behind remnants that provide key insights into stellar evolution. In systems involving white dwarfs, accretion from a companion can lead to thermonuclear instabilities, while massive binaries may culminate in core-collapse events or high-velocity disruptions.^[75]^[76] Novae represent one common end state for intermediate-mass binaries containing a white dwarf accreting hydrogen-rich material from a low-mass companion, such as a main-sequence star or subgiant. The accumulated hydrogen layer on the white dwarf's surface reaches ignition temperatures, triggering a thermonuclear runaway explosion that ejects the outer envelope at speeds of 500–3000 km/s, brightening the system by factors of 10^4 to 10^6 in visible light. These events do not destroy the white dwarf, allowing recurrence on timescales of 10^3 to 10^5 years, depending on the accretion rate and white dwarf mass, with more massive white dwarfs (around 1 M_⊙) enabling shorter intervals in recurrent novae. Observations of systems like RS Ophiuchi demonstrate this cyclic behavior, where the white dwarf regains mass between outbursts.^[77]^[78]^[77] Supernovae mark more destructive endpoints, particularly in binaries where mass transfer pushes a component beyond critical limits. Type Ia supernovae arise in single-degenerate scenarios involving a carbon-oxygen (CO) white dwarf accreting mass from a non-degenerate companion, such as a red giant or helium star, until it approaches the Chandrasekhar limit of approximately 1.4 M_⊙; carbon ignition then leads to a thermonuclear detonation that obliterates the white dwarf. This process, first proposed in the context of binary evolution, accounts for a significant fraction of observed Type Ia events and serves as a standard candle for cosmology due to their uniform peak luminosities. In massive binaries, core-collapse supernovae occur when a star with initial mass above 8 M_⊙ exhausts its fuel, forming an iron core that collapses under gravity, often after envelope stripping via mass transfer from a companion, resulting in explosions that eject heavy elements and leave neutron star or black hole remnants. Binary interactions can alter the progenitor's structure, producing stripped-envelope subtypes like Type Ib or Ic supernovae.^[79]^[79]^[75] Runaway stars emerge as high-velocity ejections from binary disruptions during these explosive phases, with peculiar velocities often exceeding 100 km/s relative to the galactic disk. In the Blaauw mechanism, a symmetric supernova explosion in a massive binary removes more than half the system's mass instantaneously, unbinding the companion and imparting it with velocity proportional to the pre-explosion orbital speed, typically 20–100 km/s. The Hills mechanism, conversely, involves an asymmetric natal kick to the compact remnant during the supernova, which can disrupt the binary even if mass loss is subcritical, accelerating the surviving star to hundreds of km/s and potentially creating hypervelocity runaways. These mechanisms explain the observed population of O and B-type runaways, with examples like AE Aurigae tracing back to the Orion Nebula cluster.^[80]^[81]^[82] Mergers represent another pathway following phases of mass transfer and common envelope evolution, where the binary components collide after orbital shrinkage. In post-main-sequence systems, such mergers can rejuvenate the stellar envelope, forming blue stragglers—hot, massive stars that appear younger than their cluster peers—through the coalescence of two lower-mass stars. More exotic outcomes include Thorne-Żytkow objects, hypothetical red supergiants with a neutron star core engulfed during a merger, where accretion onto the neutron star sustains unique nucleosynthetic signatures like elevated lithium abundances. These objects, predicted in the 1970s, challenge traditional single-star evolution models and may explain anomalous supergiants.^[83]^[83] The remnants of these end states often persist as compact object binaries, such as neutron star–black hole (NSBH) or black hole–black hole (BH–BH) pairs, formed through sequential supernovae and mass transfer in massive progenitors. These systems evolve via gravitational wave emission toward coalescence, with NSBH binaries typically arising from unequal-mass pairs where the primary collapses to a black hole and the secondary to a neutron star. Population synthesis models indicate that isolated binary evolution produces a range of remnant masses and eccentricities, influencing merger rates detectable by observatories like LIGO/Virgo. Black hole–neutron star binaries, in particular, offer probes of supernova physics and natal kicks, with observed events like GW200105 confirming their astrophysical reality.^[76]^[76]

Special Binary Types

Cataclysmic Variables

Cataclysmic variables (CVs) are semi-detached binary star systems consisting of a white dwarf primary accreting material from a low-mass companion star that fills its Roche lobe.^[84] The donor is typically a main-sequence star of spectral type K or M, with masses around 0.1–0.6 solar masses, while the white dwarf has a mass of approximately 0.6–1.2 solar masses.^[85] Mass transfer occurs through the inner Lagrange point, forming an accretion disk around the white dwarf unless disrupted by a strong magnetic field.^[86] CVs exhibit dramatic photometric variability due to instabilities in the accretion process, with brightness changes of 2–10 magnitudes occurring over timescales of days to months.^[87] In non-magnetic systems, the accretion disk is the primary source of this variability; thermal instabilities, such as the disk instability model, lead to sudden increases in accretion rate, causing outbursts as material heats up and spreads outward.^[88] The physics of these disks involves viscous heating and cooling, where partial ionization zones trigger brightness rises when the accretion rate exceeds a critical value.^[89] Subtypes of CVs are distinguished by their outburst characteristics and magnetic field strengths. Classical novae involve explosive thermonuclear fusion on the white dwarf's surface after accumulated hydrogen reaches ignition temperatures, resulting in ejections and luminosities up to 10^5 times the Sun's.^[86] Dwarf novae, comprising about 70% of CVs,^[90] show recurrent outbursts every few weeks to months due to disk instabilities rather than nuclear burning, with amplitude increases of 3–5 magnitudes.^[88] Polars, or AM Herculis systems, feature synchronously rotating white dwarfs with magnetic fields exceeding 10 million gauss, channeling accretion onto the magnetic poles and producing strong cyclotron emission without a disk.^[87] The long-term evolution of CVs begins with post-main-sequence binaries where the secondary evolves to fill its Roche lobe, initiating mass transfer driven by angular momentum loss.^[85] Primary mechanisms include gravitational radiation for short-period systems and magnetic braking for longer periods, where stellar winds interact with the magnetic field to remove angular momentum, shrinking the orbit and enhancing transfer rates.^[89] A period gap around 2–3 hours arises from disrupted magnetic braking when the secondary detaches briefly, allowing it to shrink further before resuming contact.^[85] This evolution typically spans billions of years, with CVs descending from wider binaries formed via common envelope ejection.^[91] Notable examples include SS Cygni, a prototypical dwarf nova with outbursts every 50 days, reaching visual magnitudes of 8–10 from a quiescence of 12, driven by its 6.6-hour orbital period and well-studied disk instabilities.^[92] Nova Cygni 1975 (V1500 Cyg), a classical nova in a polar system, erupted with a peak magnitude of 2.0, ejecting material at 1600 km/s and revealing a 5.5-hour orbit with strong magnetic field effects post-outburst.^[93]

X-ray Binaries

X-ray binaries are binary star systems in which a compact object—either a neutron star or a black hole—accretes matter from a less evolved companion star, heating the accreting plasma to temperatures on the order of several keV and producing intense X-ray emission.^[94] This accretion process releases gravitational potential energy, which is converted into thermal and radiative energy as the material spirals inward.^[95] The resulting X-ray spectra typically feature thermal components from bremsstrahlung radiation in the accretion disk or boundary layer around the compact object, often modified by Comptonization in a hot corona.^[95] In systems with relativistic outflows, synchrotron emission from jets can also contribute to the high-energy output, particularly at lower X-ray luminosities.^[96] Peak luminosities in these systems can reach up to approximately 10^{38} erg s^{-1}, making them among the brightest persistent X-ray sources in the Galaxy.^[97] These systems are broadly classified into low-mass X-ray binaries (LMXBs) and high-mass X-ray binaries (HMXBs) based on the mass of the donor star. In LMXBs, the companion has a mass less than about 1 M_\sun and transfers material primarily through Roche lobe overflow, leading to steady or variable accretion onto the compact object.^[94] HMXBs, in contrast, involve massive donors exceeding 8 M_\sun, where accretion often occurs via strong stellar winds or, less commonly, Roche lobe overflow in closer systems.^[98] A prominent subclass of HMXBs is the Be/X-ray binaries, featuring a Be star companion whose decretion disk interacts episodically with the compact object, resulting in transient X-ray outbursts during periastron passages.^[99] The evolutionary pathways of X-ray binaries originate from the progenitors of massive stars that undergo core collapse to form the compact accretor. During the supernova explosion, asymmetric mass ejection imparts a "natal kick" to the newborn neutron star, with velocities typically ranging from 100 to 1000 km/s; this can either widen the orbit to prevent mass transfer or tighten it to enable Roche lobe contact.^[100] Black hole formation may involve milder or no kicks due to more symmetric explosions, preserving wider binaries. Subsequent phases often include common envelope evolution, where the expanding donor engulfs the compact object, leading to orbital shrinkage and the onset of stable mass transfer. Over time, HMXBs evolve rapidly due to the short lifetimes of massive donors, while LMXBs can persist for billions of years with low-rate accretion.^[94] Notable examples illustrate these characteristics. Cygnus X-1 is a classic HMXB consisting of a black hole with a mass of approximately 15 M_\sun accreting from a massive O9.7 Iab supergiant companion via its stellar wind, producing persistent X-ray emission with a luminosity around 10^{37} erg s^{-1}. In contrast, Scorpius X-1 represents a prototypical LMXB, featuring a neutron star of about 1.4 M_\sun accreting from a low-mass companion (~0.4 M_\sun) through Roche lobe overflow, and it is the brightest persistent X-ray source in the sky with luminosities exceeding 10^{38} erg s^{-1}, classified as a Z-source due to its X-ray color-intensity diagram behavior.^[101]

Examples and Multiplicity

Notable Binary Examples

One prominent example of a visual binary is the Sirius system, consisting of Sirius A, an A1 V main-sequence star that is the brightest star in the night sky, and Sirius B, a faint white dwarf companion.^[102] The two stars orbit each other with a period of approximately 50 years, allowing their relative positions to be tracked visually over decades.^[103] Located just 8.6 light-years from Earth, this system exemplifies a case where Sirius B, originally the more massive component, transferred mass to Sirius A, resulting in Sirius B evolving into a white dwarf while Sirius A became the brighter main-sequence star.^[104] Algol, also known as Beta Persei, serves as a classic case of an eclipsing and spectroscopic binary, demonstrating active mass transfer between its components. The system has an orbital period of 2.87 days, during which the cooler, evolved subgiant donor (Algol B) periodically eclipses the hotter main-sequence star (Algol A), causing its characteristic brightness dips.^[105] Evidence for mass transfer is evident in the "Algol paradox," where the less massive donor has expanded due to Roche lobe overflow, reversing the initial mass ratio and leading to observed period increases over time.^[106] This semi-detached configuration highlights how binaries can drive the evolution of their stars through ongoing accretion onto the gainer.^[107] Eta Carinae represents an extreme massive binary with a highly eccentric orbit, known for its dramatic historical outbursts. The primary, a luminous blue variable, and its Wolf-Rayet companion orbit with a period of 5.5 years and eccentricity of about 0.9, bringing them as close as approximately 2 AU at periastron.^[108] This configuration drives colliding stellar winds, producing periodic X-ray brightenings and contributing to the Great Eruption of the 1840s, which ejected the Homunculus Nebula and temporarily made Eta Carinae one of the brightest stars.^[109] With component masses around 90 and 30 solar masses, the system illustrates the violent interactions possible in high-mass binaries nearing instability.^[110] Polaris, the nearest classical Cepheid variable, is a binary where the close companion influences the primary's pulsations. The Cepheid Polaris Aa pulsates with a period of about 4 days, but its 30-year orbital period with the companion Polaris Ab introduces perturbations that alter the pulsation amplitude and radial velocity curve.^[111] Observations suggest the companion's gravitational influence perturbs the Cepheid's atmosphere during periastron passages, potentially contributing to observed changes in pulsation properties over decades.^[112] This interaction provides a unique probe into how binarity affects standard candles used for distance measurements. A recent discovery challenging binary formation models near supermassive black holes is the young D9 system (D9-V1A/B) in the S cluster around Sagittarius A*. Identified in 2024, this binary consists of stars with masses of 2.80 and 0.73 solar masses, orbiting with a period of 372 days and a semi-major axis of 1.59 AU.^[113] Its stability over nearly two decades of observations, despite proximity to the black hole's tidal forces, implies in situ formation or capture, contradicting expectations that such dense environments disrupt young binaries. This system offers insights into star formation in galactic centers.^[114]

Multiple Star Systems

Multiple star systems consist of three or more stars gravitationally bound together, typically arranged in hierarchical configurations to maintain long-term stability. In such systems, an inner binary orbits a more distant tertiary star, with the outer orbit being significantly wider—often by a factor of 5 to 10 or more—to prevent chaotic interactions that could lead to ejections or collisions. This hierarchical structure is stabilized through higher-order gravitational perturbations, including octupole-level dynamics, which influence the long-term evolution of the orbits without disrupting the overall architecture.^[115] Observations indicate that multiple star systems with three or more components constitute approximately 10% of solar-type stellar systems in the solar neighborhood, with higher multiplicities becoming progressively rarer; for instance, quadruple systems account for about 0.1-1% of all systems. Notable examples include the quadruple system in Nu Scorpii, which features two tight inner binaries orbiting a common center at greater separation. Among more massive stars, the prevalence of triples and higher multiples rises, reaching up to 30% for early-type O and B stars. These systems often serve as the binary cores familiar from simpler pairs, but their added companions introduce complex interactions.^[116]^[117] The dynamics of multiple systems are dominated by secular perturbations, particularly the Kozai-Lidov mechanism, where the gravitational influence of the outer companion induces oscillations in the eccentricity and inclination of the inner binary's orbit. These cycles can drive the inner binary's eccentricity from near-circular to highly elongated states over timescales of thousands to millions of years, potentially leading to mass transfer episodes or stellar collisions if tidal effects are insufficient to dampen the oscillations. In quadruple and higher systems, such dynamics can propagate across hierarchical levels, enhancing instability risks but also facilitating unique evolutionary pathways like binary-binary mergers.^[118] Formation of multiple star systems primarily occurs through turbulent fragmentation of collapsing molecular cloud cores, where gravitational instabilities lead to simultaneous or near-simultaneous formation of multiple protostellar embryos within a shared envelope. Alternatively, sequential processes—such as disk fragmentation around an initial binary or dynamical captures during cluster interactions—can build higher multiplicities over time, though the former dominates for close hierarchies observed in the field. These mechanisms naturally produce the wide outer orbits essential for stability, with simulations showing that about 60% of wide binaries form via core fragmentation events at separations of 1000-3500 AU.^[68]^[119] Prominent examples illustrate the diversity of multiple systems. The Alpha Centauri system is a nearby triple, comprising the close binary Alpha Centauri AB orbited by the distant red dwarf Proxima Centauri at about 13,000 AU, making it the closest such system to Earth at 4.3 light-years. More complex is the sextuple Castor system, featuring three spectroscopic binaries in a hierarchical arrangement with outer separations exceeding 1000 AU, demonstrating stable multiplicity over billions of years.^[1]

Astrophysics and Current Research

Binary Stars and Exoplanets

Planets in binary star systems are classified into two primary configurations based on their orbital architecture relative to the stellar pair. S-type planets orbit one of the two stars at a distance closer than the binary separation, resembling circumstellar orbits perturbed by the companion star, while P-type planets, also known as circumbinary planets, orbit the common center of mass of both stars at a greater distance.^[120] Stability zones for these orbits are constrained by gravitational interactions; for S-type configurations, stable regions typically lie within approximately one-third to one-half of the binary semi-major axis to avoid ejection, whereas P-type orbits remain stable beyond about two to three times the binary separation, as determined by numerical simulations of long-term dynamical evolution. These stability limits, first systematically mapped in seminal work, ensure that planets can persist for billions of years without chaotic perturbations disrupting their paths. Detection of circumbinary planets has primarily relied on the transit method, which is particularly effective in eclipsing binary systems where the stars' mutual alignments allow for observable dips in combined stellar light from planetary transits. The Kepler space telescope mission identified over 10 such systems between 2011 and 2018, revolutionizing the field by confirming the existence of stable planetary orbits around binaries.^[121] A landmark discovery was Kepler-16b, the first unambiguously confirmed circumbinary planet, detected through multiple transits of its Saturn-mass world across the dimming light of its K-type and M-type binary hosts, located 200 light-years away. Subsequent Kepler findings, such as the multi-planet Kepler-47 system with three confirmed worlds, demonstrated that circumbinary architectures can support diverse planetary populations, including potential super-Earths in resonant orbits. The formation of planets in binary systems faces unique challenges due to the gravitational influence of the companion star, which truncates the protoplanetary disks around each host. In close binaries (separations under 50 AU), tidal forces limit disk radii to about one-third of the binary distance, reducing the material available for planet assembly and shortening disk lifetimes compared to isolated single-star environments.^[122] This truncation effect correlates with lower planet occurrence rates; surveys indicate that the frequency of giant planets in such binaries is roughly 50% that of single stars, though overall rates across wider binaries approach parity with singles.^[122] Despite these hurdles, in situ formation models suggest that circumbinary planets can emerge from a shared outer disk, with migration dynamics aiding their settling into stable P-type orbits.^[123] Habitability assessments for binary planets emphasize the role of dynamical perturbations in maintaining liquid water zones amid varying stellar illumination. In P-type systems, the binary's orbital motion induces periodic flux changes, but stable configurations can sustain habitable climates for Earth-like worlds, as simulations show resilience against eccentricity-driven instabilities over gigayear timescales.^[124] S-type planets experience stronger perturbations from the companion, potentially destabilizing inner habitable zones through secular resonances, though moderate separations allow for viable analogs. Kepler-16b exemplifies a "Tatooine-like" system, where its orbit yields dual sunsets but lies outside the habitable zone due to its gas-giant nature and cooler stellar hosts. Broader studies confirm that 50-60% of binary pairs could host dynamically stable habitable planets, expanding the search for life-bearing worlds.^[125] In 2025, citizen science initiatives have bolstered efforts to detect planets in eclipsing binaries by expanding catalogs of candidate hosts. NASA's Eclipsing Binary Patrol project, hosted on Zooniverse, enabled volunteers to classify over 320,000 light curves from TESS data, uncovering 7,936 new eclipsing binary systems and bringing the vetted total to more than 10,000.^[126] These additions enhance transit and timing variation searches for hidden planets, particularly in circumbinary setups where mutual eclipses facilitate precise orbital modeling.

Recent Discoveries and Implications

In 2024, analytical models of star cluster formation validated aspects of the capture theory for binary star origins, demonstrating that dynamical interactions among three unbound stars can efficiently produce bound binaries in dense environments like young clusters.^[127] This finding, by Y. B. Ginat and H. B. Perets, challenges earlier dominance of fragmentation models and favors the formation of soft binaries with superthermal eccentricity, influencing estimates of stellar multiplicity in the Milky Way.^[127] A landmark 2024 observation identified the first confirmed young binary system, D9, orbiting within 0.04 light-years of Sagittarius A*, the Milky Way's supermassive black hole.^[128] Detected using the Very Large Telescope's GRAVITY instrument, D9 consists of a Herbig Ae/Be primary and a T Tauri secondary in a stable ~1-year orbit, surrounded by gas and dust indicative of recent formation.^[129] This discovery suggests that star formation persists in the extreme gravitational field near galactic centers, potentially reshaping models of black hole feedback and stellar dynamics in nuclear star clusters.^[128] Advancing understanding of binary evolution, 2025 studies from Purdue University analyzed circumbinary disks around young binaries, revealing distinct migration patterns driven by disk torques.^[130] Through hydrodynamic simulations, researchers found that these disks induce eccentric orbits in embedded binaries, accelerating inward migration by factors of 2-5 compared to isolated systems. Such mechanisms imply faster binary coalescence in protoplanetary environments, with broader implications for the efficiency of planet formation around multiple stars.^[130] The 2020s brought observational confirmation of predicted "zombie" stars—post-merger remnants of white dwarf binaries that survive incomplete detonations. At the Center for Astrophysics | Harvard & Smithsonian (CfA), detailed spectroscopy of systems like J005311 revealed carbon-oxygen compositions and rapid winds consistent with merged white dwarfs reignited by collision energy.^[131] These rare objects, observed via Hubble and ground-based telescopes, validate theoretical models of Type Ia supernova progenitors and suggest that up to 10% of such events may leave detectable remnants, refining cosmic distance measurements.^[132] Gravitational wave astronomy has revolutionized binary research since the first detection in 2015, with LIGO/Virgo/KAGRA detecting over 200 merging compact binaries as of 2025, including the black hole pair GW150914. Recent events, such as GW230529 involving a neutron star-black hole merger, provide mass and spin constraints that trace evolutionary paths from massive star binaries. The fourth observing run (O4), concluded on November 18, 2025, detected over 200 additional signals, more than doubling previous totals and providing new constraints on binary evolution.^[133] These detections imply a higher merger rate in dense environments, informing population synthesis models and the role of binaries in heavy element production. Citizen science efforts peaked in 2025 with NASA's TESS mission, where volunteers validated 7,936 new eclipsing binaries from full-frame images, expanding the catalog to 10,001 systems.^[126] This Zooniverse-led classification refined ephemerides for periods from hours to years, enabling precise stellar parameter calibration.^[134] The dataset highlights underrepresented short-period binaries, advancing benchmarks for binary fraction in the solar neighborhood and exoplanet transit validation.^[135] A 2024 study from the Instituto de Astrofísica de Canarias (IAC) examined aging effects in red giant binaries, showing that tidal interactions circularize orbits as stars expand.^[136] Using asteroseismology on nearly 1,000 systems, researchers measured eccentricity reductions from ~0.3 to <0.1 over gigayears, driven by convective envelope growth.^[136] This evolution implies synchronized spins and mass transfer triggers, with implications for common envelope phases and supernova kick velocities in evolved populations.^[136] Instrumental advances in 2025 included first light for the STELES spectrograph on the Southern Astrophysical Research (SOAR) Telescope, targeting the massive binary Eta Carinae.^[137] Capturing high-resolution spectra across 3,000-10,000 Å, STELES resolved orbital velocity shifts in the system's 5.5-year cycle, revealing wind collisions and ejecta chemistry.^[137] This capability promises detailed monitoring of luminous blue variables, enhancing models of binary-driven eruptions and their role in galactic chemical enrichment.^[138]

References

[1]
Multiple Star Systems - NASA Science
Oct 22, 2024 · Three separate pairs of stars orbit each other in typical binary fashion. But two of these pairs also orbit one another. The third pair, at a ...
[2]
Binary Stars
Binary stars include visual, spectroscopic, and eclipsing types. Examples are Algol, the first known eclipsing binary, and Sirius A & B.
[3]
Imagine the Universe! - X-ray Binary Stars
Sep 23, 2021 · Binary star systems contain two stars that orbit around their common center of mass. Many of the stars in our Galaxy are part of a binary system ...
[4]
Friedrich Bessel: Discoverer of White Dwarf Sirius B | AMNH
His observations revealed that Sirius was slowly changing its position as if it were being pulled around in orbit by the gravity of another star.
[5]
Discovering Sirius B
The dark star associated with Sirius was accidentally discovered on the evening of January 31, 1862 in Cambridgeport Massachusetts.
[6]
John Goodricke | Variable Star, Periodic Comet & Deafness
Sep 13, 2025 · In November 1782 he was regularly observing the star known as Algol and soon realized that its brightness varies regularly over a period of a ...Missing: date | Show results with:date
[7]
Hermann Carl Vogel - Linda Hall Library
Apr 3, 2019 · In 1889, Vogel discovered that light from the star Algol alternates between blue shifts ... spectroscopic binaries to be discovered ...
[8]
Antonia Maury - Linda Hall Library
Mar 21, 2019 · Shortly therafter, in 1890, Miss Maury discovered the second such binary, β Aurigae. She also spent many years studying a spectroscopic binary ...
[9]
Henry Norris Russell | American Astronomer & Astrophysicist
Oct 21, 2025 · He also developed statistical methods for estimating the distances, motions, and masses of groups of binary stars. Russell generally employed a ...
[10]
Naming Stars - International Astronomical Union | IAU
Stars in binary or multiple systems are labelled in various ways: by capital letters from the Latin alphabet if the star has a common colloquial name; by Bayer ...
[11]
August's Night Sky Notes: Seeing Double - NASA Science
Aug 1, 2024 · Binary stars are two stars that are gravitationally bound and orbit each other, and optical double stars only appear to be close together when ...
[12]
Lesson Plans: Time that period! (Information about binary stars)
May 7, 2015 · Binary Stars. About half of the stars visible in the night sky are not single stars at all, but are actually multiple star systems or double ...
[13]
How far can a pair of stars be separated and still maintain a stable ...
Jan 3, 2018 · An ultrawide binary with a separation of 0.5 parsec (1.6 light-years) is statistically likely to break up within just 100 million years, while a ...
[14]
Deriving Kepler's Formula for Binary Stars - Imagine the Universe!
Sep 23, 2020 · Your astronomy book goes through a detailed derivation of the equation to find the mass of a star in a binary system.
[15]
Binary Stars | ASTRO 801: Planets, Stars, Galaxies, and the Universe
Binary stars are stars gravitationally bound to one or more partners, often forming from gas clumps. Visual binaries are rare, and most are too far away to see ...
[16]
https://courses.ems.psu.edu/astro801/content/l5_p7.html
[17]
A photometric and spectroscopic study of eight semi-detached ...
Eclipsing binary stars are categorised into three classes: detached, semi-detached, and those in contact based on their Roche lobe configurations (Kopal 1959; ...
[18]
l5S7 - JILA
When both stars in a binary system are smaller than their respective Roche lobes, no mass transfer will occur. Such systems are called detached binary systems.Missing: configurations | Show results with:configurations
[19]
[PDF] Introduction to Astrophysics
These are called detached binaries in which the stars evolve nearly independently. Most binaries are like this even when the stars have evolved to be red giants ...
[20]
W Ursae Majoris: The Parameters of A Contact Binary
Spectroscopic radial velocity observations of W Ursae Majoris, the prototype contact binary, are reported. The parameters (masses, radii, luminosities) of the ...
[21]
The evolution of wide binary stars - Oxford Academic
Abstract. We study the orbital evolution of wide binary stars in the solar neighbourhood due to gravitational perturbations from passing stars. We include.
[22]
Close Binary Stars - an overview | ScienceDirect Topics
Close binary stars are defined as pairs of stars ... Visual binaries usually have wide separations and the two components can be resolved by telescopes.
[23]
Week 1: Observed Stellar Properties, Binary Stars
Jan 5, 2015 · Visual binary: The two stars of the binary are resolved in a telescope. One star is observed to move on an elliptical orbit relative to the ...
[24]
star_sirius.html - UNLV Physics
As the image illustrates, the angular separation of Sirius A and Sirius B is order of magnitude 10''. The human eye angular resolution has the typical and ...
[25]
The Sirius System and Its Astrophysical Puzzles - IOP Science
In the present-day orbit, the separation of Sirius A and B ranges from 31.5 au at maximum to 8.1 au at periastron. If the progenitor of B had a mass of ...<|control11|><|separator|>
[26]
NASA's Hubble Sees a Stellar Volcano
Oct 16, 2024 · Located approximately 700 light-years away, a binary star system called R Aquarii undergoes violent eruptions that blast out huge filaments of ...
[27]
Visual Binary Star Observations - Astrophysics Data System
Visual observations of selected binary stars were obtained by utilizing EMCC campus astronomical equipment. ... Stars 5.1 Selected Examples Figure 12 ...Missing: definition | Show results with:definition
[28]
Measuring Stellar Masses – Astronomy - Maricopa Open Digital Press
Through a telescope, as Riccioli discovered in 1650, Mizar can be seen to have another, closer companion that does orbit it; Mizar is thus a visual binary.
[29]
[PDF] Measuring the Properties of Stars - UCCS
Jun 6, 2007 · A few binary stars are easy to see with even a small telescope. Mizar, the middle star in the handle of the Big Dipper, is a good example. When ...
[30]
[PDF] Astrometry: Revealing the Other Two Dimensions of Velocity Space
First physical binary resolved by the telescope was Mizar, generally credited to Giovanni Ricciolo (1598 – 1671) in about. 1650. It now appears that Galileo ...
[31]
Visual Binaries in the Orion Nebula Cluster - ADS
We have carried out a major survey for visual binaries toward the Orion Nebula Cluster, using images obtained with the Advanced Camera for Surveys on the ...
[32]
Comparison of Gaia and Hipparcos parallaxes of close visual binary ...
The study compares Gaia and Hipparcos parallaxes for binary stars, finding Gaia DR2 parallaxes significantly more accurate, impacting mass determinations.<|control11|><|separator|>
[33]
Binary Stars - ESA Science & Technology
In the area of binary and multiple stars Gaia's important contribution will be to make controlled statistical studies of multiple star distribution functions.Missing: properties prevalence NASA
[34]
[PDF] chapter 18 spectroscopic binary stars 18.1
The radial velocity curve is given by equation 18.2.12: (. ). cos. ) cos(. 1.
[35]
Single-lined Spectroscopic Binary Star Candidates ... - IOP Science
Sep 23, 2019 · A probability function for the detection of RV variations is used for identifying SB1 candidates. The estimation of orbital parameters for main- ...
[36]
MONOS.II. Orbit review and analysis for 35 single-lined ... - arXiv
Jun 16, 2021 · In this 2nd paper, we tackle the study of the 35 single-line spectroscopic binary (SB1) systems identified in the previous paper of the series.
[37]
DOUBLE-LINED SPECTROSCOPIC BINARY STARS IN THE RAVE ...
Jun 8, 2010 · We devise a new method for the detection of double-lined binary stars in a sample of the Radial Velocity Experiment (RAVE) survey spectra.
[38]
CHARACTERISTICS OF THE SPECTROSCOPIC BINARIES IN THE ...
The frequency of spectroscopic binaries with periods less than about 2000 days among the extreme Population II stars is found to be at least 20%, and agrees ...
[39]
Angular momentum evolution of Algol binaries - Oxford Academic
The only difference between the tables is the fourth column in Table 2 where SB1 and SB2 refer to the single- and double-lined Algols, respectively. The ...
[40]
Eclipsing Binary Star - an overview | ScienceDirect Topics
An eclipsing binary star is defined as a member of a binary or multiple star system whose orbital alignment allows for eclipses to occur, enabling the analysis ...
[41]
KEPLER ECLIPSING BINARY STARS. I. CATALOG AND ...
Here we present a comprehensive catalog of eclipsing binary stars observed by Kepler in the first 44 days of operation, the data being publicly available ...Missing: utility seminal
[42]
On the Determination of the Orbital Elements of Eclipsing Variable ...
SAO/NASA ADS Astronomy Abstract Service. ON THE DETERMINATION OF THE ORBITAL ELEMENTS OF ECLIPSING VARIABLE STARS. II' B~ HENRY NORRIS RUSSELL PART III.Missing: paper | Show results with:paper
[43]
The Light Curve of the Eclipsing Binary Star XX Leo - NASA ADS
The shape of the combined light curves is symmetric, with secondary minima midway between primary minima (indicating circular or nearly circular orbits).
[44]
Light-Curve Analyses of Eclipsing Binaries - IOP Science
The secondary component is redder than the main sequence and slightly fainter than V = 20. That the primary component is near the main sequence and slightly ...
[45]
ellc: A fast, flexible light curve model for detached eclipsing binary ...
A binary star model (ellc) that can be used to analyse the light curves of detached eclipsing binary stars and transiting exoplanet systems that is fast and ...Missing: utility seminal
[46]
[PDF] TESS Eclipsing Binary Stars. I. Short-cadence Observations of 4584 ...
Jan 12, 2022 · Astronomers have studied EBs for over two centuries, ever since John Goodricke suggested in 1782 that eclipses are responsible for Algol's.
[47]
[PDF] Eclipsing Binary Observing Guide - British Astronomical Association
There are three basic types of Eclipsing Binary which are classified on the shape of their light curves.
[48]
[PDF] Eclipsing binary stars as tests of stellar evolutionary models and ...
Abstract. Eclipsing binary stars provide highly accurate measurements of the fundamental physical properties of stars. They therefore serve as stringent ...
[49]
Algol (Beta Persei): Eclipsing Variable Star in Perseus
Apr 28, 2019 · Algol, Beta Persei, is a bright multiple star located in Perseus. It is the second brightest star in the constellation, after Mirfak, Alpha Persei.
[50]
[PDF] Spectroscopic, eclipsing binary stars - mass, radius and temperature
Jun 19, 2023 · The ratio of the temperatures of the two stars can also be estimated by measuring how much the flux received from the binary star dips in the ...
[51]
https://www.constellation-guide.com/algol/
[52]
The astrometric orbit of a binary
The semi-major axis (i-e half of the ellipses) is respectively denoted a1, a2 and a0 for the primary, secondary and photocentre orbit. Since the origin is ...<|separator|>
[53]
Proxima's orbit around α Centauri - Astronomy & Astrophysics (A&A)
We show that Proxima and α Cen are gravitationally bound with a high degree of confidence. The orbital period of Proxima is ≈ 550 000 yr.
[54]
[1611.03495] Proxima's orbit around Alpha Centauri - arXiv
Nov 10, 2016 · We show that Proxima and Alpha Cen are gravitationally bound with a high degree of confidence. The orbital period of Proxima is approximately 550 000 years.
[55]
Gaia Data Release 3 - Astrometric binary star processing
The significance of the orbital model is defined as the semi-major axis of the orbit, a0, divided by its uncertainty. This definition of the significance was ...Missing: photocenter | Show results with:photocenter
[56]
Binary Star Systems - The Astrophysics Spectator
The orbital periods of the majority of binary stars are between 1/3 and 300,000 years, with the median at 14 years.
[57]
[PDF] Investigation of orbital period changes in 9 contact binaries - arXiv
Aug 22, 2023 · We analyzed the time series for these objects to detect any secular changes in their orbital period. The precise period of these 9 binary ...
[58]
Orbital Evolution in Binary and Triple Stars, with an Application to SS Lacertae - IOPscience
No readable text found in the HTML.<|separator|>
[59]
Secular Period Changes in Ten Eclipsing Binaries - NASA ADS
... system has been secularly decreasing at least for the last three decades. ... star to explain the observed secular period decrease in TV Cas. Conservative ...
[60]
Eclipsing binary stars: what can we learn?
the orbital plane lies along our line of sight, so that each star eclipses the other once per orbit · we can measure the depths and times of the eclipses ...
[61]
Center of Mass - Eclipsing Binary Stars - NAAP - UNL Astronomy
The formula expresses the idea that adding up the product of each mass times its distance from the coordinate system origin and then dividing by the sum of ...
[62]
Binary Star Systems - Richard Fitzpatrick
Figure 20 shows an example binary star orbit, in the center of mass frame, calculated with $m_1/m_2=0.5$ and $e=0.2$ . Here, the triangles and squares ...
[63]
[PDF] Binary Stars Consider a binary composed of two stars of masses M1 ...
Binary Stars. Consider a binary composed of two stars of masses M1 and M2. We define M = M1 + M2 and µ = M1M2/M. If a1 and a2 are the mean.
[64]
Distribution of mass ratios in spectroscopic binaries - NASA ADS
... K1/K2 (2) where K1 and K2 are the semi-amplitudes of radial velocity of the primary and secondary components respectively. The histogram of Q of the 72 ...
[65]
Lecture 10: How Massive is a Star?
Jan 17, 2025 · Thus, the total mass of a binary system can be found from the relation M1 + M2 = a3/P2 , as long as the values of a & P are known. Note that ...
[66]
The contribution of binary star formation via core fragmentation on ...
The authors suggest that the peak at 75 AU is caused by disc fragmentation, while the peak at 3000 AU is likely caused by fragmentation of protostellar cores.
[67]
Binary star formation and the outflows from their discs
The formation of binary star systems is believed to be triggered by the fragmentation of protostellar cores as they collapse. Each core produces around on ...
[68]
binary fractions in the massive young Large Magellanic Cloud star ...
In this paper, we analyse the binary-fraction properties of two young massive LMC clusters, NGC 1805 and NGC 1818. Previous studies of these clusters have ...
[69]
Polar alignment of a circumbinary disc around a brown dwarf binary
Analytical calculations show that a critical tilt angle of icrit ≳ 50○ for moderately eccentric binaries is needed for polar alignment of circumbinary discs in ...
[70]
[PDF] 1984ApJ. . .211 . .355W The Astrophysical Journal, 277:355-360 ...
As a result, the accretor is swallowed up in the envelope of the giant (Webbink 1919a) and spirals inward through the common envelope (Paczynski 1976). This ...
[71]
[PDF] Binaries and stellar evolution
Gray scales indicate the three possible stable binary configurations: detached (dark), semi-detached (mid- dle) and contact (light gray).
[72]
Binary-stripped Stars as Core-collapse Supernovae Progenitors
We present a systematic simulation study of single and binary-stripped stars with the same initial mass as candidates for core-collapse supernovae (11–21 M⊙).
[73]
Detailed binary evolution models of coalescing neutron star – black ...
In this paper, we present the population properties of merging NSBH systems and their progenitors such as component masses, orbital features, and BH spins.
[74]
[1804.06880] The Masses and Accretion Rates of White Dwarfs in ...
Apr 18, 2018 · Title: The Masses and Accretion Rates of White Dwarfs in Classical and Recurrent Novae ... dwarf novae, for most of the time between nova ...
[75]
Scientists catch a white dwarf star in the act of exploding into a nova
Aug 19, 2016 · Novae are typically caused by a gravitationally locked pair of stars, called a binary system, consisting of one white dwarf and a companion star ...
[76]
Progenitors of type Ia supernovae: Binary stars with white dwarf ...
The exploding star is thought to be a carbon–oxygen (CO) white dwarf (WD) that accretes mass from a binary companion until it approaches the Chandrasekhar limit ...Introduction · White Dwarf + Main-Sequence... · Dwarf Novae
[77]
Enigma of Runaway Stars Solved - ESO
Runaway stars are heavy stars moving at high velocities, likely accelerated by a supernova explosion of a companion star in a binary system.Missing: Hills | Show results with:Hills
[78]
Neutron stars colliding with binary companions: formation of ...
In cases where the binary is disrupted by the first SN, the companion star can be hurled out and be observed as runaway stars ('Blaauw mechanism'; Blaauw 1961).
[79]
The effects of sudden mass loss and a random kick velocity ...
... supernova explosion if the neutron star is given a kick velocity 332 HILLS Vol. 267 comparable to the initial orbital velocity of the binary. This suggests ...
[80]
The Evolution of Massive Stellar Multiplicity in the Field - arXiv
Dec 17, 2024 · Stellar mergers have been associated with blue stragglers (e.g., Hills & Day, 1976a; Stryker, 1993; Bailyn, 1995; Perets, 2015) , magnetic stars ...
[81]
[2410.02896] Thorne-Żytkow Objects - arXiv
Oct 3, 2024 · One interesting example of a binary merger product are Thorne-Żytkow Objects (TŻOs), stars that look like red supergiants but contain neutron stars at their ...
[82]
Cataclysmic Variables - Imagine the Universe! - NASA
Cataclysmic variables (CVs) are binary star systems that have a white dwarf and a normal star companion. They are typically small.
[83]
[1108.4716] The Evolution of Cataclysmic Variables - arXiv
Aug 23, 2011 · The first part outlines the theoretical principles of CV evolution, focusing specifically on the standard "disrupted magnetic braking" model.
[84]
Introduction to Cataclysmic Variables (CVs) - HEASARC
Dec 11, 2017 · CVs are binary systems that consist of an normal star and a white dwarf. They are typically small - a typical binary system is roughly the size of the Earth- ...
[85]
https://arxiv.org/abs/1108.4716
[86]
[astro-ph/0701654] Cataclysmic Variables - arXiv
Jan 23, 2007 · Novae draw their energy from nuclear reactions, while dwarf novae rely on gravity to power their smaller eruptions. All the different classes of ...
[87]
A unified model for the evolution of cataclysmic variables
The secular evolution of CVs is driven by the loss of angular momentum, which leads to the secondary filling its Roche lobe and commencing mass transfer.
[88]
cataclysmic variables: an empirical angular momentum loss ...
The evolution of a CV is driven by angular momentum loss; it has long been known that low-mass stars lose angular momentum from a magnetic wind (e.g., Weber. & ...
[89]
Physics of Cataclysmic Variable Investigated by X-ray Spectroscopic ...
The dwarf nova SS Cygni was discovered in 1896, the second following U Gem in 1855. As shown in Fig. 2a, explosions occur at an interval of 50 days or so ...<|control11|><|separator|>
[90]
On a polar Nova Cygni 1975 (V1500 Cyg) - NASA ADS
Patterson and Raymond (1985a) found a correlation between LXILV and A~( present among known cataclysmic variables. Due to its small value of i%~f~ Nova Cyg 1975 ...Missing: examples SS
[91]
[2206.10053] Low-Mass X-ray Binaries - arXiv
Jun 21, 2022 · In this Chapter, we review the phenomenology of sub-classes of these systems and summarize observational finding regarding their characteristics ...
[92]
[PDF] X-RAY EMISSION FROM COMPACT SOURCES
In this paper, I will review the basic physics which produces X-ray emission from neutron stars and black holes, focusing primarily on accretion, which is.
[93]
On the peak radio and X-ray emission from neutron star and black ...
Radio emission from X-ray binaries is generally believed to originate in incoherent synchrotron emission from a large volume of electrons (and maybe also ...
[94]
[2009.03244] Advances in Understanding High-Mass X-ray Binaries ...
Sep 7, 2020 · In this review, we provide a broad but concise summary of the physical processes dominating the emission from high mass X-ray binaries across virtually the ...
[95]
X-ray binaries | The Astronomy and Astrophysics Review
The various types and classes of X-ray binary are reviewed high-lighting recent results. The high mass X-ray binaries (HMXRBs) can be used to probe the nat.
[96]
effects of high-velocity supernova kicks on the orbital properties and ...
We systematically investigate the effects of high supernova kick velocities on the orbital parameters of post-supernova neutron-star binaries.
[97]
The origin of Scorpius X-1 - Astronomy & Astrophysics
It is the prototype low-mass X-ray binary composed of a compact object and a donor star that have masses of 1.4 M and 0.42 M , respectively (Steeghs & Casares ...
[98]
[PDF] sirius.pdf
Mar 30, 2017 · Sirius, the seventh-nearest stellar system, is a visual binary containing the metallic-line A1 V star Sirius A, brightest star in the sky, ...
[99]
[PDF] The interferometric diameter and internal structure of Sirius A - arXiv
As the orbital period is rela- tively short (50 years), two revolutions of the Sirius A-B binary have already been measured, allowing Gatewood &. Gatewood (1978) ...
[100]
The Dog Star, Sirius, and its Tiny Companion - NASA Science
Dec 13, 2005 · This picture is an artist's impression showing how the binary star system of Sirius A and its diminutive blue companion, Sirius B, might appear ...<|control11|><|separator|>
[101]
[PDF] Algol, January 1999 Variable Star Of The Month - Astronomy in Hawaii
Algol is an eclipsing binary star system 93 light-years away as determined by the Hipparcos ... Animated simulation of Algol's hydrodynamic mass transfer (900K ...
[102]
Modes of Mass Ejection by Binary Stars and the Effect ... - NASA ADS
INTRODUCTION The observed period of an eclipsing binary is defined as the ... That the increase in period of i3 Lyrae is due to mass transfer from the ...
[103]
Determination of mass loss and mass transfer rates of Algol (Beta ...
An ultraviolet study of the semi-detached eclipsing binary star system TT Hydrae. TT Hydrae is an Algol-type interacting binary star consisting of a B9.5 V ...
[104]
NASA's NuSTAR Mission Proves Superstar Eta Carinae Shoots ...
cosmic rays — into space.
[105]
[PDF] Eta Carinae in the Context of the Most Massive Stars
In the 1840's η Carinae underwent a giant outburst and ejected a nebula which we call the Homunculus. The event was so impressive that η Carinae was classified ...
[106]
When Winds Collide: The Supermassive Binary Eta Carinae
Apr 30, 2015 · The high orbital eccentricity (e = 0.9) also causes large changes in stellar separation—from about 29 astronomical units (AU) (the distance ...Missing: period | Show results with:period
[107]
The Spectroscopic Orbit of Polaris, and its Pulsation Properties - arXiv
Sep 6, 2023 · Polaris is the nearest and brightest classical Cepheid, and pulsates with a period of about 4 days. It has long been known as a single-lined spectroscopic ...Missing: star | Show results with:star
[108]
[PDF] arXiv:2309.03257v1 [astro-ph.SR] 6 Sep 2023
Sep 6, 2023 · ABSTRACT Polaris is the nearest and brightest classical Cepheid, and pulsates with a period of about 4 days. It has long been known as a single ...
[109]
https://ntrs.nasa.gov/api/citations/20090038698/downloads/20090038698.pdf
[110]
A binary system in the S cluster close to the supermassive black ...
Dec 17, 2024 · The detection of D9 implies that binary systems in the S cluster have the potential to reside in the vicinity of the supermassive black hole Sgr ...Results · Keplerian Orbit · Supplementary Note 1
[111]
The evolution of hierarchical triple star-systems
Dec 23, 2016 · The structures of observed triples tend to be hierarchical, i.e. the triples consist of an inner binary and a distant star (hereafter outer ...
[112]
The evolution of stellar triples - The most common evolutionary ...
The fraction of triples is considerable. About 10% of systems with F- & G-type primary stars are triples (Eggleton & Tokovinin 2008; Raghavan et al. 2010; ...<|control11|><|separator|>
[113]
Secular dynamics of hierarchical multiple systems composed of ...
Abstract. We present a method for studying the secular gravitational dynamics of hierarchical multiple systems consisting of nested binaries, which is vali.
[114]
Dynamical evolution of triple-star systems by Lidov–Kozai cycles ...
A common mechanism to explain the short-period pile-up present in the observations is the migration through Lidov–Kozai cycles combined with tidal friction.
[115]
[PDF] architecture of hierarchical stellar systems and their formation
Sep 18, 2021 · In this review, I focus on multi- ple systems containing three or more stars and attempt to link their architecture to potential formation ...
[116]
[PDF] On the stability of planetary orbits in binary star systems I. The S-type ...
Jun 3, 2021 · S-type orbits are internal orbits around one of the two stars in a binary system, unlike P-type orbits around both stars.
[117]
The search for circumbinary planets - SSW - ESA Cosmos
Since the discovery of Kepler-16b in 2011, 14 circumbinary planets have been discovered in 12 systems by transit missions.
[118]
Properties of planets in binary systems - Astronomy & Astrophysics
On one hand, the frequency of planets in binary systems has a strong effect on the global frequency of planets, more than half of solar type stars being in ...
[119]
Birth Locations of the Kepler Circumbinary Planets - arXiv
Apr 2, 2015 · The Kepler mission has discovered about a dozen circumbinary planetary systems, all containing planets on ~ 1 AU orbits. We place bounds on the ...
[120]
The Resilience of Habitable Climates Around Circumbinary Stars
Aug 25, 2020 · Earth-like planets in dynamically stable orbits in circumbinary systems are as likely to remain as habitable as planets in single-star systems.Missing: analogs | Show results with:analogs<|separator|>
[121]
Habitability Properties of Circumbinary Planets - IOPscience
Jun 2, 2017 · It is shown that several habitability conditions (in fact, at least seven such conditions) appear to be fulfilled automatically by circumbinary planets of main ...
[122]
NASA Citizen Scientists Find New Eclipsing Binary Stars
Jun 26, 2025 · When two stars orbit one another in such a way that one blocks the other's light each time it swings around, that's an eclipsing binary.Missing: definition properties prevalence ESA review<|control11|><|separator|>
[123]
Three-body binary formation in clusters: analytical theory
Binary formation in clusters through triple encounters between three unbound stars ... Generozov & Perets 2023). In this paper, we wish to study three-body binary ...
[124]
First ever binary star found near our galaxy's supermassive black hole
Dec 17, 2024 · An international team of researchers has detected a binary star orbiting close to Sagittarius A*, the supermassive black hole at the centre ...
[125]
A binary system in the S cluster close to the supermassive black ...
Dec 17, 2024 · Here, we report the detection of a spectroscopic binary system in the S cluster with the masses of the components of 2.80 ± 0.50 M⊙ and 0.73 ± ...
[126]
New discovery sheds light on binary star formation and evolution
Apr 8, 2025 · The findings, which focus on the orbital behavior of binary stars surrounded by circumbinary disks, offer new insight into the formation and ...
[127]
Winds of Merged White Dwarfs - AAS Nova
May 3, 2024 · When white dwarfs collide, the merger product may have a strong magnetic field and powerful winds, as may be the case for WD J005311.
[128]
Rapid Variability in the Wind from the White Dwarf Merger ...
The optical spectrum of the "zombie star" white dwarf merger candidate J005311 is similar to that of WO-type Wolf-Rayet (WR) stars; however the maximum ...
[129]
validated Eclipsing Binary Stars detected in Full-Frame Image data ...
Jun 5, 2025 · Here we present a catalog of 10001 uniformly-vetted and -validated eclipsing binary stars that passed all our ephemeris and photocenter tests, as well as ...
[130]
The TESS Ten Thousand Catalog: 10,001 Uniformly Vetted and ...
Here we present a catalog of 10,001 uniformly vetted and validated eclipsing binary stars that passed all our ephemeris and photocenter tests, as well as ...
[131]
Study reveals how binary stars change their stellar dance with age
Jul 31, 2024 · Binary stars, systems comprising two stars that are gravitationally bound, are treasure troves for stellar astrophysics.Missing: prevalence review
[132]
New Instrument at SOAR Achieves First Light with Observations of ...
Sep 26, 2025 · The long-awaited instrument achieved first light in August with observations of the binary star system Eta Carinae, along with 13 other targets.
[133]
Telescope sees binary star's beautiful rainbow spectra - Space
Oct 2, 2025 · A new rainbow spectrum from the STELES instrument on Chile's SOAR Telescope captures Eta Carinae in unprecedented detail.