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Quark-nova

A quark-nova is a hypothetical explosive transition in stellar evolution where a neutron star rapidly converts into a more compact quark star through the deconfinement of its hadronic matter into strange quark matter, releasing approximately $10^{53} ergs of energy primarily as neutrinos and kinetic energy in ejecta.^[1] This event, first proposed in 2002 by Rachid Ouyed and colleagues, arises from the Bodmer-Witten hypothesis that stable strange quark matter could exist at extreme densities, triggering an exothermic phase transition when a neutron star accretes mass or spins down sufficiently. The conversion begins at the core via strange quark seeding, propagating outward as a combustion front or deflagration wave, leading to gravitational collapse and the expulsion of a thin shell of neutron-rich material with velocities ranging from Newtonian to ultra-relativistic (Lorentz factors up to hundreds).^[2] The quark-nova model integrates quantum chromodynamics principles with general relativity, predicting distinct observational signatures that differentiate it from core-collapse supernovae or neutron star mergers.^[2] Neutrino emissions peak at luminosities exceeding $10^{53} erg/s with a harder spectrum (average temperature ~20 MeV), potentially detectable by advanced observatories like Super-Kamiokande or Hyper-Kamiokande, unlike the softer spectra from standard supernovae.^[2] Electromagnetically, it can manifest as gamma-ray bursts if the ejecta is relativistic, super-luminous supernovae when interacting with prior supernova remnants, or fast radio bursts through magnetar-like mechanisms in the nascent quark star.^[2] Astrophysically, quark-novae offer explanations for enigmatic transients and processes: they may power long-duration gamma-ray bursts via collapsar-like scenarios involving Wolf-Rayet star companions, contribute to r-process nucleosynthesis by providing neutron-rich environments for heavy element formation, and influence cosmic reionization through high-redshift events.^[2] Proposed candidates include the super-luminous supernova SN 2006gy and certain double-peaked light curves in Type IIn supernovae, where a delayed quark-nova reignites the explosion.^[3] Furthermore, the model challenges standard Type Ia supernova cosmology by suggesting some events as quark-nova detonations in neutron star-white dwarf binaries, potentially resolving tensions in dark energy measurements from the Hubble diagram.^[4] Ongoing research, including simulations of ejecta dynamics and neutrino signals, continues to test the quark-nova's viability against multi-messenger observations.^[5]

Theoretical Foundations

Quark Matter and Stars

Quark matter represents a hypothetical phase of matter described by quantum chromodynamics (QCD), in which quarks and gluons become deconfined from hadrons under extreme conditions of high density and temperature. This deconfinement occurs at densities exceeding nuclear saturation density, approximately $10^{17} kg/m³, where the strong nuclear force no longer binds quarks into protons and neutrons, allowing them to exist freely as a plasma-like state.^[6]^[7] The theoretical foundation for quark matter arises from the QCD phase diagram, which maps the states of strongly interacting matter as a function of temperature and baryon chemical potential. At high densities corresponding to the cores of compact stars, QCD predicts a transition to deconfined quark matter, potentially including lighter up and down quarks alongside heavier strange quarks to achieve beta equilibrium. A seminal hypothesis posits that strange quark matter—composed of roughly equal numbers of up, down, and strange quarks—could be the absolute ground state of baryonic matter, more stable than nuclear matter under certain conditions. This idea, proposed by Witten in 1984, suggests that ordinary nuclei might be metastable excitations above this true vacuum.^[8] Quark stars, also known as strange stars, are hypothetical ultra-dense compact objects formed entirely from quark matter, with typical masses of 1–2 solar masses and radii around 10 km, comparable to neutron stars but supported by a distinct equation of state. Unlike neutron stars, which rely on neutron degeneracy pressure, quark stars exhibit a stiffer equation of state due to the Pauli exclusion principle acting on deconfined quarks, leading to higher maximum masses and potentially sharper mass-radius relations. If strange quark matter is the ground state of matter, these stars could be absolutely stable; otherwise, they might exist in metastable configurations where the energy per baryon exceeds that of iron nuclei but is separated by a significant energy barrier preventing decay.^[9]^[10] A simple phenomenological description of quark matter is provided by the MIT bag model, which confines quarks within a "bag" to mimic QCD confinement. The energy density in this model for thermal quark-gluon plasma is given by

\varepsilon = \frac{\pi^2}{90} g T^4 + B,

where g is the number of degrees of freedom (typically 37–51 for quarks and gluons), T is the temperature, and B is the bag constant representing the vacuum energy difference, with values ranging from 50–100 MeV/fm³. At zero temperature relevant to compact stars, the thermal term vanishes, leaving the degenerate Fermi gas contribution plus B, which enforces stability against hadronization.^[11]

Neutron Star to Quark Star Transition

The transition from a neutron star to a quark star occurs when the central density exceeds a critical value of approximately 4–5 times the nuclear saturation density, triggering the deconfinement of quarks and the formation of quark matter in the core.^[12] This critical density can be reached through several mechanisms, including the spin-down of a rapidly rotating neutron star, which increases central density as centrifugal support diminishes; mass accretion from a companion in a binary system, pushing the star beyond the Tolman–Oppenheimer–Volkoff mass limit adapted for the onset of the quark phase; or the merger of two neutron stars, where post-merger densities briefly surpass deconfinement thresholds.^[13]^[14] These processes destabilize the hadronic equation of state, favoring the more stable quark matter phase. The phase transition is typically first-order, involving a discontinuous jump in density across the phase boundary and the release of substantial latent heat, estimated at around 10^{53} erg for a typical neutron star conversion.^[15] This exothermic process drives a combustion-like front through the star, converting hadronic matter to quark matter layer by layer. The conversion initiates in the core at radii on the order of 10 km, with the propagating front maintaining a thin structure on the order of 10–100 cm wide and advancing at subsonic speeds up to ~0.1c in turbulent regimes.^[16] The concept of quark stars as compact objects composed of deconfined quark matter was first proposed by Itoh in 1970, who explored their hydrostatic equilibrium using early models of degenerate quark gas.^[17] The possibility of a dynamical transition within neutron stars, including explosive deconfinement during core collapse or later evolution, was later refined by Madsen in 1998 and 1999, linking it to supernova explosions and the stability of strange quark matter.^[18]^[13] Subsequent studies, such as those modeling the two-step conversion from nuclear to two-flavor and then three-flavor quark matter, have emphasized the rapid timescales (milliseconds) and hydrodynamic instabilities involved.^[19] The resulting quark star, more compact than its neutron star progenitor, exhibits enhanced stability under general relativity.

The Quark-Nova Mechanism

Collapse Dynamics

The quark-nova begins with the rapid conversion of a neutron star's hadronic core into stable quark matter, primarily composed of up, down, and strange quarks, under extreme densities exceeding the deconfinement threshold. This phase transition induces a sudden gravitational collapse of the core, as the equation of state for quark matter is stiffer yet allows for a smaller equilibrium radius compared to neutron matter, leading to a contraction on timescales of approximately 0.1 milliseconds. The collapse creates a density discontinuity, propagating outward as a detonation front at the speed of sound in quark matter (about c / \sqrt{3}), which rebounds into a shock wave that disrupts the overlying neutron-rich envelope.^[20] The hydrodynamic evolution involves an outward-propagating detonation or deflagration front that accelerates and ejects the outer layers of the neutron star, with masses up to about 0.01 solar masses. This explosive ejection is driven by the pressure from the rebounding shock and the release of gravitational potential energy, potentially generating gravitational waves that carry away a fraction of the energy. If the post-conversion mass exceeds the stability limit for quark stars, further collapse into a black hole becomes possible. Recent models as of 2025 include delayed phase transitions leading to quark or hybrid stars.^[20]^[21] Trapped neutrinos play a crucial role in providing additional pressure support during the collapse, thermalizing within the dense core and contributing to the explosion dynamics through a burst lasting from milliseconds to seconds. The mean free path of these neutrinos is short (~500 cm at 10 MeV energies), ensuring efficient energy deposition that aids in driving the shock. The primary energy release stems from the change in gravitational binding energy due to the radius reduction of 5-10 km, approximated by the formula

\Delta E \approx \frac{GM^2 \Delta R}{R^2},

where G is the gravitational constant, M is the core mass, R is the initial neutron star radius, and \Delta R is the contraction amount, yielding total energies on the order of $10^{52} to $10^{53} ergs.^[20] This dynamical sequence is detailed in the theoretical framework developed by Ouyed and collaborators, starting with the foundational model of neutrino-driven mass ejection and extended to include remnant evolution and angular momentum effects.^[20]

Energy Output and Emissions

The total energy budget of a quark-nova is estimated at approximately $10^{53} erg, arising primarily from the gravitational binding energy released during the neutron star's core collapse and the latent heat associated with the phase transition to quark matter (approximately 100 MeV per baryon).^[22]^[23] This output exceeds that of a typical supernova by about an order of magnitude in kinetic energy while being orders of magnitude greater than a classical nova, positioning the quark-nova as an intermediate explosive event in stellar evolution.^[24] The energy partitioning in a quark-nova favors efficient conversion into observable forms, with roughly 10% escaping as neutrinos due to trapping within the dense core, and about 1% imparting kinetic energy to the ejecta (typically $10^{-4} to $10^{-2} M_\odot of neutron-rich material expelled at velocities corresponding to Lorentz factors of a few to tens).^[25]^[26] The remainder is distributed among photons and potentially cosmic rays, with the photon component enhanced in scenarios involving color-flavor-locked quark matter that suppresses standard neutrino emission channels.^[22] Particle emissions during the quark-nova include an intense neutrino flux of order $10^{58} particles, carrying a hard spectrum peaking around 60 MeV from the deconfinement process.^[23] Gamma-rays arise from pion decays in the hot, deconfined environment, while the neutron-rich ejecta facilitates r-process nucleosynthesis, producing heavy elements beyond atomic mass A=130.^[22] The peak luminosity reaches approximately $10^{44} erg/s over durations of days, driven by the rapid energy injection.^[22] This luminosity can be approximated using a blackbody model as L \approx \frac{dE}{dt} = 4\pi R^2 \sigma T^4, where the initial temperature T is $10^9 to $10^{10} K, reflecting the hot photosphere formed by the expanding ejecta.^[26]

Predicted Observational Features

Light Curves and Spectra

The light curve of a quark-nova is expected to exhibit a rapid rise to peak luminosity over approximately hours, driven by the expansion of the low-mass (~0.01 M_⊙), neutron-rich ejecta launched at velocities up to ~0.3c during the neutron star to quark star transition.^[27] This short diffusion timescale arises from the ejecta's small optical depth and high expansion speed, distinguishing it from the slower rise (~weeks) typical of core-collapse supernovae. Numerical simulations indicate a bolometric luminosity of ~10^{43} erg/s around 1 day post-event, powered by thermal energy deposited in the ejecta via neutrino interactions during the phase transition.^[27] Following the peak, the light curve declines steeply over days as the ejecta cools adiabatically and the photosphere recedes, potentially featuring a brief plateau if radioactive heating from trace nickel in the ejecta contributes significantly, though such heating is minimal in isolated quark-novae.^[3] A distinguishing feature is the narrower peak width compared to Type II supernovae, reflecting the compact ejecta mass and reduced adiabatic losses. In scenarios where the newborn quark star acts as a central engine, spin-down luminosity can power a late rebrightening, resulting in a double-peaked profile with the secondary hump appearing days to weeks later.^[28] Spectral evolution begins with a hot blackbody continuum in the UV-optical regime at peak, corresponding to photospheric temperatures of ~10^5 K, consistent with reheating of the ejecta to initial core temperatures exceeding 10^8 K before rapid expansion cools the emitting surface.^[3] As the ejecta expands and cools over hours to days, the spectrum shifts toward softer energies, potentially incorporating X-ray or gamma-ray components from ongoing shock heating or non-thermal processes in the inner regions. Prominent emission lines from heavy elements (A > 130), produced via r-process nucleosynthesis in the neutron-rich ejecta, are predicted to emerge in the optical and near-infrared spectra, providing a unique signature of the event's extreme conditions. These features contrast with standard supernova spectra by showing enhanced abundances of r-process material without requiring a massive progenitor envelope.^[29]

Multi-Messenger Signals

Quark-novae are predicted to emit a hyperburst of approximately $10^{58} electron antineutrinos with typical energies in the range of 10-50 MeV, arising from the rapid deconfinement and thermal processes during the neutron star to quark star transition. This neutrino signal features a harder spectrum compared to those from proto-neutron stars in core-collapse supernovae, with peak luminosities exceeding $10^{53} erg s^{-1}.^[2] The burst duration is significantly shorter than in core-collapse supernovae, on the order of milliseconds to seconds due to the compact core size and efficient neutrino escape. The neutrino light curve is expected to peak approximately 1 second before the electromagnetic counterpart, stemming from the near-instantaneous core conversion followed by the propagation of the explosion shock through the neutron star envelope. This temporal offset enables precursor detection, distinguishing quark-novae from other transients. For Galactic events at distances of ~10 kpc, the energy fluence reaches ~$10^{7} erg cm^{-2}, primarily in electron antineutrinos detectable via inverse beta decay. Observatories like IceCube and Super-Kamiokande could register thousands of events from sources within a few kpc, providing a clear multi-messenger alert.^[2] Gravitational waves from quark-novae originate in the asymmetric collapse dynamics or rapid differential rotation during the phase transition. These signals fall within the 100-1000 Hz sensitivity band of detectors like LIGO and Virgo, with peak amplitudes enhanced by rotational effects in the progenitor neutron star. The waveform would exhibit characteristic high-frequency oscillations tied to the core bounce and decompression, offering a unique signature for identification. If the ejecta becomes collimated, quark-novae may produce gamma-ray bursts through synchrotron emission in relativistic outflows, serving as an electromagnetic counterpart. Additionally, shocks in the expanding shell could accelerate particles to ultra-high energies, contributing to cosmic ray populations via diffusive shock acceleration.^[30] These non-electromagnetic messengers collectively enable comprehensive probing of the event, with joint detections enhancing constraints on quark matter properties.

Candidate Events and Evidence

Proposed Candidates

Several astronomical events have been proposed as potential quark-novae based on criteria such as exceptional luminosity exceeding typical supernovae by factors of 100 or more, rapid photometric evolution including double-peaked light curves, high-velocity ejecta suggestive of a secondary explosion, and associations with neutron star remnants or unusual multi-wavelength emissions.^[31] These candidates are identified through matches to quark-nova model predictions, including reheating of supernova ejecta by the quark-star formation energy release, though none have been definitively confirmed.^[31] One prominent candidate is the superluminous supernova SN 2006gy, discovered in 2006 within the galaxy NGC 1260 at a redshift of z = 0.019 (approximately 240 million light-years away).^[32] It reached a peak absolute visual magnitude of about -22, making it over 100 times brighter than a standard Type IIn supernova, with a slow rise to maximum over ~70 days followed by prolonged high luminosity.^[33] In the quark-nova model, this is interpreted as a core-collapse supernova at t = 0 followed by a quark-nova ~15 days later, where the conversion of the neutron star to a quark star injects ~10^{52} erg into the ejecta (mass ~60 M_\sun), reheating it to ~0.4 MeV and powering the extended light curve while reducing adiabatic cooling losses.^[31] Similarly, SN 2005ap, a Type II supernova discovered in 2005, has been proposed as a quark-nova due to its extreme brightness—potentially the most luminous supernova observed at the time—and a double-humped light curve with a rapid 1-3 week rise to peak followed by quick decline.^[34] The event exhibited high-velocity ejecta exceeding 23,000 km/s, consistent with a quark-nova ejecta velocity of ~25,000 km/s impacting supernova material ~40 days post-explosion in a spherical configuration.^[31] This secondary energy injection explains the unusual luminosity and evolution without invoking pair-instability mechanisms.^[31] The gamma-ray burst GRB 060218, detected on February 18, 2006, and associated with the supernova SN 2006aj at z = 0.0335, features an extended X-ray plateau lasting ~1,000 seconds that aligns with quark-nova model expectations for sustained energy output from quark-star formation following a low-luminosity core-collapse event. The burst's total isotropic energy (~10^{49} erg) and thermal blackbody emission during the plateau suggest a compact progenitor with neutron star involvement, where the quark-nova provides the prolonged powering mechanism. More recent proposals link quark-novae to fast radio bursts (FRBs), such as FRB 20200120E, a repeating source discovered in 2020 and localized to a globular cluster in the nearby galaxy M81 (z ~ 0.0007).^[35] In the quark-nova framework, the event's low dispersion measure (~87 pc/cm³) and persistence in an old stellar environment imply a neutron star accreting mass until a phase transition to a quark star, producing the coherent radio emission without a supernova optical counterpart. Recent studies (as of 2025) further validate the Quark-Nova model against FRB observations, including repeating sources like FRB 20200120E.^[36] This association fits environments with massive neutron stars, predicting ~10-20 such detectable candidates in future surveys like the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST). Overall, these events show model-consistent features like unexpected energy budgets and temporal structures, but require multi-messenger follow-up for validation.^[31]

Supporting Observations

Efforts to detect quark-novae (QNe) rely on multi-wavelength monitoring of recent core-collapse supernovae and their remnants, targeting signatures such as rapid optical fading, X-ray bursts, and radio emissions. Ground-based optical searches using CCD-equipped telescopes with apertures of 0.3–1 m have been organized to scan fields around young neutron stars for transient events occurring days to weeks post-supernova, as coordinated through collaborative observer networks.^[37] X-ray observatories like Chandra provide constraints by monitoring supernova remnants for anomalous high-energy emissions indicative of neutron-to-quark star transitions, while Hubble's ultraviolet and optical imaging resolves ejecta structures potentially altered by QN shocks. Recent James Webb Space Telescope (JWST) observations of remnants, such as the 2024 survey of Cassiopeia A, provide enhanced sensitivity to dust-enshrouded ejecta and chemical anomalies, aiding in the identification of spallation products from QN neutron winds.^[38] Statistical analyses of neutron star populations infer QN rarity, with models estimating their occurrence at approximately 5 × 10^{-5} the rate of core-collapse supernovae, or roughly one per 20,000 such events, based on binary evolution scenarios involving common-envelope phases in massive stars.^[28] This low frequency arises from the specific conditions required for neutron star deconfinement, limiting direct detections despite extensive transient surveys. No direct QN observations exist to date, but indirect evidence emerges from anomalous supernova remnants like Cassiopeia A (Cas A), where NuSTAR X-ray data reveal a decoupling of iron and titanium-44 distributions, with enhanced titanium in the northwest quadrant and depleted iron, consistent with spallation by relativistic neutrons from a QN explosion days after the initial supernova.^[39] Chandra and Hubble observations of Cas A further highlight irregular ejecta kinematics and a lack of a prominent pulsar wind nebula around the central compact object, features attributable to QN disruption of the nascent neutron star. Pulsar timing anomalies, including anti-glitches in anomalous X-ray pulsars, provide additional indirect support, as these can be modeled as interactions between quark stars and fallback debris from QN events.^[40] Detecting QNe faces significant challenges, including confusion with other transients like superluminous supernovae or kilonovae, which exhibit similar rapid light-curve evolutions and multi-wavelength signatures.^[28] Confirmation requires multi-messenger coincidence, particularly neutrino detections from quark deconfinement, though current detectors like IceCube face low event rates and background noise from galactic supernovae.^[41]

Broader Implications

Links to Fast Radio Bursts

Theoretical models propose that quark-novae (QNe) can serve as progenitors for fast radio bursts (FRBs) through the formation of magnetar-like quark stars, which generate coherent radio emission via shocks in the surrounding medium. In this scenario, the rapid transition of a neutron star to a quark star during a QN event ejects relativistic "chunks" that interact with ionized plasma, producing millisecond-duration bursts of radio waves. This mechanism aligns with observed FRB characteristics, such as their high brightness and short timescales.^[36] The emission process in the QN-FRB model involves magnetic reconnection or crust fracturing in the newborn quark star, releasing approximately $10^{40} erg of energy in coherent synchrotron radiation at GHz frequencies. These bursts arise from collisionless shocks formed as QN ejecta propagate through the interstellar medium, with the radio signal modulated by plasma effects that influence the observed dispersion. The model specifically reproduces key FRB properties, including dispersion measures (e.g., around 286 pc cm^{-3}) and repetition patterns, through "angular" repetitions separated by hours and "radial" ones spanning days, driven by instabilities in the ejecta dynamics.^[36] Observational evidence supporting this link includes associations between FRBs and young stellar remnants, such as FRB 20200120E located near a globular cluster, which may trace back to an ancient QN event in a dense environment. The QN-FRB framework predicts that roughly 10% of detected FRBs originate from QNe, a fraction that can be tested using large-scale surveys like CHIME/FRB, which monitor repetition rates and host galaxy properties to distinguish QN contributions from other progenitors.^[36]

Relation to Supernovae and Mergers

Quark-novae are proposed to occur as a delayed explosion following the formation of a neutron star during a Type II core-collapse supernova, interacting with the supernova ejecta and contributing to the overall energetics.^[42] This process involves the rapid conversion of the neutron star's core to quark matter, releasing energy on the order of $10^{52} erg, which can power the extreme luminosity observed in superluminous supernovae (SLSNe).^[43] For instance, dual-shock models of quark-novae interacting with supernova ejecta have been invoked to explain the broad H\alpha spectral features and light curve bumps in several SLSNe, such as SN 2006gy and SN 2011kl.^[43] These events bridge the gap between standard core-collapse mechanisms and the anomalous brightness of SLSNe, potentially accounting for a subset of hydrogen-poor explosions without requiring magnetar spin-down or pair-instability scenarios.^[31] In the context of compact object mergers, quark-novae may arise in neutron star binaries where one or both stars undergo conversion to quark stars prior to or during the merger, leading to delayed explosions after the initial coalescence.^[44] The formation of a quark star in such systems can destabilize the remnant, triggering a quark-nova days to years post-merger due to continued decompression or spin-down.^[45] This delayed phase contrasts with the prompt gravitational wave and kilonova signals from standard neutron star mergers, offering a pathway for multi-messenger follow-up observations. A 2025 study on quark star merger ejecta identifies three primary outcomes based on the binding energy of quark matter: formation of a stable quark star with neutron-rich ejecta enabling r-process nucleosynthesis; prompt collapse to a black hole with minimal emission; or a quark-nova if the remnant exceeds stability limits, producing distinct kilonova-like transients.^[46] These relations have broader implications for heavy element production, as neutron-rich ejecta from quark-nova phases in mergers can contribute to r-process nucleosynthesis, synthesizing elements beyond iron in environments distinct from standard kilonovae.^[46] Although the exact fraction remains uncertain, models suggest that quark matter phases may play a role in up to a few percent of observed kilonovae, altering their color and duration.^[46] Evolutionarily, quark-novae connect neutron star cooling behaviors—characterized by rapid neutrino-dominated phases—to quark star observables, where reduced heat capacity leads to steeper luminosity decline curves observable in X-ray afterglows.^[47] This linkage aids in distinguishing hybrid compact objects in binary populations.

Research Developments

Theoretical Models

Theoretical models of quark-novae primarily rely on one-dimensional (1D) and two-dimensional (2D) hydrodynamic simulations that incorporate quantum chromodynamics (QCD) equations of state to describe the rapid conversion of a neutron star into a quark star. The Ouyed group's Quark-Nova (QN) code, developed as part of the Quark Nova Project at the University of Calgary, exemplifies these core models by simulating the explosive phase transition and its dynamical effects on surrounding stellar material.^[5]^[28] These codes model the deconfinement of quarks from hadronic matter, predicting energy releases on the order of $10^{52} erg, which drive shock waves and outflows.^[28] Micro-physical processes in these simulations include detailed treatments of neutrino transport, weak interactions, and pion condensation within the dense core. Neutrino transport is crucial for capturing energy dissipation and lepton number conservation during the transition, often implemented via multi-moment schemes to account for radiative transfer in opaque environments.^[2] Weak interactions facilitate the conversion process by enabling beta equilibrium adjustments, while pion condensation emerges as a stabilizing mechanism in the strange quark matter phase, influencing the equation of state at high densities.^[48] A comprehensive review highlights how these elements couple to produce characteristic thermal and non-thermal signatures in the ejecta.^[2] On the macro-physical scale, models incorporate the effects of angular momentum conservation and magnetic field amplification, which shape the explosion dynamics and remnant properties. Angular momentum leads to differential rotation in the quark star, potentially powering jets or enhancing fallback accretion, while magnetic fields, amplified by flux freezing during the collapse, can reach strengths of $10^{15} G and influence outflow collimation.^[48] These factors are simulated using magnetohydrodynamic extensions to the base codes, revealing how they contribute to transient phenomena like superluminous supernovae.^[49] Recent advancements include comparisons of the QN model with fast radio burst (FRB) observations, published in 2025, which integrate the stability of strange quark matter to predict burst luminosities and repetition patterns. These models assume a bag model equation of state with a bag constant around 145 MeV, yielding stable quark matter configurations that align with observed FRB energy scales of $10^{38-40} erg. Recent 2025 modeling demonstrates how quark-nova shocks can reproduce the light curve and spectra of SN 2023aew, delivering ~$10^{52} erg over ~40 days.^[21] Such developments refine predictions for multi-messenger signals, including gamma-ray counterparts.^[50] Despite progress, limitations persist due to uncertainties in the bag constant, which parameterizes the QCD vacuum energy and varies between 50-200 MeV across models, affecting the transition energetics. The speed of the phase transition also remains poorly constrained, with deflagration or detonation fronts introducing variability in explosion yields. Furthermore, current 1D/2D frameworks lack the full treatment of instabilities, underscoring the need for three-dimensional general relativistic magnetohydrodynamic (GRMHD) simulations to capture turbulence and gravitational effects accurately.^[2]^[51]

Challenges and Future Prospects

One of the primary challenges in quark-nova theory is the lack of direct observational evidence, as no confirmed events have been identified despite proposals linking them to enigmatic transients like super-luminous supernovae and gamma-ray bursts.^[2] This absence stems from the rarity of the underlying process—a neutron star converting to a quark star via deconfinement—and the subtlety of distinguishing quark-nova signatures from those of conventional supernovae or neutron star mergers.^[5] Additionally, quark-novae exhibit ambiguity with other astrophysical transients, such as short-hard gamma-ray bursts, due to overlapping light curve features like prompt emission and X-ray plateaus, complicating unambiguous identification.^[52] Theoretical modeling is further hindered by uncertainties in quantum chromodynamics (QCD) at extreme densities, where perturbative approaches yield inconsistent equations of state for quark matter, affecting predictions of explosion dynamics and remnant properties.^[53] Theoretical gaps persist in understanding the role of color superconductivity in quark-nova scenarios, where Cooper pairing of quarks could alter the energy release and stability of the nascent quark star, yet its incorporation into dynamical models remains incomplete.^[54] A related uncertainty involves neutrino opacity in quark matter, particularly in strange quark stars, as recent studies highlight how absorption processes in color-superconducting phases dominate at low temperatures but shift with rising thermal energy, impacting cooling rates and multi-messenger signals. Future prospects for confirming quark-novae hinge on advanced observatories capable of multi-messenger detections by 2030. Gravitational waves from quark star mergers or related binaries may be accessible to the Laser Interferometer Space Antenna (LISA), revealing phase transitions through post-merger waveforms.^[55] Optical transients with double-humped light curves, a predicted quark-nova hallmark, could be surveyed by the Rubin Observatory's Legacy Survey of Space and Time (LSST), enabling rapid follow-up of millions of events.^[5] Neutrino bursts from deconfinement, potentially enhanced in color-superconducting matter, offer detection opportunities with IceCube-Gen2, which will expand sensitivity by an order of magnitude for high-energy astrophysical sources.^[56] The Quark Nova Project at the University of Calgary, active since the 2000s, forecasts that 2025–2030 surveys will yield evidence through heavy-element nucleosynthesis in remnants and Type Ia supernova signatures, testable via these facilities.^[5] A potential breakthrough lies in multi-messenger coincidences, such as aligned gravitational waves, neutrinos, and electromagnetic counterparts, which could confirm deconfinement signatures by distinguishing quark matter formation from hadronic processes in compact object events.^[57]

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Jun 21, 2004 · Abstract: We explore the role of neutrinos in a Quark Nova explosion. We study production of neutrinos during this event, their propagation ...
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https://arxiv.org/abs/2505.08737
[22]
https://arxiv.org/pdf/0708.1787.pdf
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https://doi.org/10.3390/universe8060322
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https://arxiv.org/pdf/1601.04235.pdf
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https://arxiv.org/pdf/1510.06135.pdf
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Neutrino Emission and Mass Ejection in Quark Novae - IOPscience
We explore the role of neutrinos in a quark nova explosion. We study the production of neutrinos during this event, their propagation, and their ...
[27]
Quark-Novae in massive binaries: a model for double-humped ...
We show that a Quark-Nova (QN; explosive transition of the Neutron Star – NS – to a quark star –QS) occurring in a massive binary, experiencing two Common ...Missing: Madsen | Show results with:Madsen
[28]
[0911.5424] Predictions for signatures of the quark-nova in ... - arXiv
Nov 28, 2009 · Predictions for signatures of the quark-nova in superluminous supernovae. Authors:Rachid Ouyed (1 and 2), Denis Leahy (1), Prashanth Jaikumar (3 ...
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Impact of Rotation on the Multimessenger Signatures of a Hadron ...
Sep 26, 2022 · We study the impact of rotation on the multimessenger signals of core-collapse supernovae (CCSNe) with the occurrence of a first-order hadron- ...
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Astronomy & Astrophysics (A&A)
- **Status**: Content not found at https://www.aanda.org/articles/aa/abs/2002/39/aa20982/aa20982.html.
[31]
[astro-ph/0301575] Ultra-high energy cosmic rays from Quark Novae
Abstract: We explore acceleration of ions in the Quark Nova (QN) scenario, where a neutron star experiences an explosive phase transition into a quark star ...
[32]
[0708.1787] Supernova SN2006gy as a first ever Quark Nova? - arXiv
Aug 13, 2007 · Supernova SN2006gy as a first ever Quark Nova? Authors:Denis Leahy, Rachid Ouyed (University of Calgary, Calgary, Alberta, Canada).Missing: original | Show results with:original
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Supernova 2006gy in NGC 1260 - NASA/ADS
... SN 2006gy is located at R.A. = 3h17m27s.06, Decl. = +41d24'19".5 (equinox 2000.0), which is 2".0 west and 0".4 north of the center of NGC 1260 (z = 0.019 ...
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SN 2006gy: Discovery of the most luminous supernova ever ... - arXiv
Dec 21, 2006 · We report our discovery and observations of the peculiar Type IIn supernova SN2006gy in NGC1260, revealing that it reached a peak magnitude of -22.
[35]
https://ui.adsabs.harvard.edu/abs/2021ApJ...910L..18B/abstract
[36]
https://academic.oup.com/mnras/article/537/3/2876/7994425
[37]
The Hunt for the Quark-Nova: A Call for Observers - NASA ADS
We seek CCD-equipped observers with modest-sized telescopes to join a collaborative effort to search for these events. ... The ADS is operated by the Smithsonian ...Missing: surveys | Show results with:surveys
[38]
A JWST Survey of the Supernova Remnant Cassiopeia A - IOPscience
A thermonuclear explosion (Kushnir & Katz 2015) or quark nova (Ouyed et al. ... This work is based on observations made with the NASA/ESA/CSA James Webb Space ...
[39]
Hints of a second explosion (a quark nova) in Cassiopeia A ... - arXiv
Apr 20, 2014 · We show that the explosive transition of the neutron star (NS) to a quark star (QS) (a Quark Nova) in Cassiopeia A (Cas A) a few days following the SN proper
[40]
https://ui.adsabs.harvard.edu/abs/2014Ap&SS.352..715O/abstract
[41]
Detectability of neutrino-signal fluctuations induced by the hadron ...
We introduce a systematic and quantitative methodology for establishing the presence of neutrino oscillatory signals due to the hadron-quark phase ...
[42]
Quark-Nova model for FRBs: model comparison with observational ...
Here, we explore further our model for FRBs based on the Quark-Nova (QN) model as presented in detail in Ouyed et al. (2021) (hereafter, first paper). A QN is a ...
[43]
[1906.09559] A Quark-Nova in the wake of a core-collapse Supernova
Jun 23, 2019 · Access Paper: View a PDF of the paper titled A Quark-Nova in the wake of a core-collapse Supernova: a unifying model for long duration Gamma ...Missing: dynamics | Show results with:dynamics
[44]
[1206.7113] Quark Nova Signatures in Super-luminous Supernovae
Jun 29, 2012 · In this work we study the light curves of eight ... Predictions of spectral signatures unique to the dual-shock quark nova are presented.
[45]
Gamma Ray Bursts from delayed collapse of neutron stars to quark ...
Sep 13, 2002 · We propose a model to explain how a Gamma Rays Burst can take place days or years after a supernova explosion.Missing: nova merger
[46]
[1505.05764] Quark-Novae in massive binaries : a model for double ...
May 21, 2015 · Quark-Novae in massive binaries : a model for double-humped, hydrogen-poor, superluminous Supernovae. Authors:Rachid Ouyed, Denis Leahy, Nico ...
[47]
[2411.09013] Equation of State of Decompressed Quark Matter, and ...
Nov 13, 2024 · For relatively high binding energies, quark star mergers are unlikely to produce r-process elements and kilonova signals. We propose that future ...
[48]
Cooling curves for neutron stars with hadronic matter and quark matter
Dec 8, 2011 · In our models, the dominant early-stage cooling process is neutrino emission via the direct Urca process. As a consequence, the cooling curves ...
[49]
[1505.08147] Quark Nova Model for Fast Radio Bursts - arXiv
May 29, 2015 · The model allows indirect measurement of neutron star magnetic fields and periods in addition to providing astronomical measurements of \beta- ...
[50]
The Macro-Physics of the Quark-Nova: Astrophysical Implications
Oct 14, 2025 · PDF | A quark-nova is a hypothetical stellar evolution branch where a neutron star converts explosively into a quark star.
[51]
QUARK-NOVAE OCCURRING IN MASSIVE BINARIES - IOP Science
Feb 9, 2016 · QUARK-NOVAE OCCURRING IN MASSIVE BINARIES: A UNIVERSAL ENERGY SOURCE IN SUPERLUMINOUS SUPERNOVAE WITH DOUBLE-PEAKED LIGHT CURVES. Rachid Ouyed, ...
[52]
[2408.01834] The Quark-Nova model for FRBs - arXiv
Aug 3, 2024 · Abstract:We utilize the Quark-Novae (QN) model for Fast Radio Bursts (FRBs; Ouyed et al. 2021; arXiv:2005.09793) to evaluate its performance ...Missing: progenitor | Show results with:progenitor
[53]
[PDF] On the formation of strange quark stars from supernova in compact ...
Jul 30, 2025 · We calculated the equivalent configuration using the quark EOS1 (left plot) and the quark EOS2 (right plot), maintaining the same angular ...
[54]
QUARK-NOVAE IN LOW-MASS X-RAY BINARIES WITH MASSIVE ...
QUARK-NOVAE IN LOW-MASS X-RAY BINARIES WITH MASSIVE NEUTRON STARS: A UNIVERSAL MODEL FOR SHORT-HARD GAMMA-RAY BURSTS. Rachid Ouyed, Jan Staff, and Prashanth ...Missing: Madsen | Show results with:Madsen
[55]
[PDF] Comparing strange and nonstrange quark stars within resummed ...
Sep 9, 2025 · This allows us to obtain the mass-radius relation for pure quark stars and compare the results with the predictions from perturbative QCD (pQCD) ...
[56]
Supernovae, hypernovae and color superconductivity - Inspire HEP
We argue that Color Superconductivity (CSC, Cooper pairing in quark matter leading to the breaking of SU(3) color symmetry) may play a role in triggering ...Missing: nova | Show results with:nova
[57]
Modeling quark star merger ejecta: Study reveals three possible ...
Sep 29, 2025 · The findings offer a potential way to finally distinguish quark stars from neutron stars through kilonova observations. "The implications of ...
[58]
[2108.05292] The IceCube-Gen2 Neutrino Observatory - arXiv
Aug 11, 2021 · IceCube-Gen2 will increase the rate of observed cosmic neutrinos by an order of magnitude, be able to detect five-times fainter neutrino sources ...Missing: quark- nova
[59]
Signatures for quark matter from multi-messenger observations - arXiv
Apr 10, 2019 · We survey the proposed signatures and emphasize the importance of data from neutron star mergers, which provide access to dynamical properties ...