Collapsar model

Collapsar model
Credit: NASA/CXC/M.Weiss · Public domain · source
Name	Collapsar model
Field	Astrophysics

Collapsar model The Collapsar model describes a class of astrophysical scenarios in which the core collapse of a massive, rotating star leads to a black hole and an accretion disk that powers relativistic jets. It connects to observations of long-duration Gamma-ray bursts, certain Type Ib and Type Ic supernovae, and high-energy transients associated with massive stellar endpoints. Developed through theoretical work and computational modeling, the model links concepts from stellar evolution, compact-object formation, and high-energy astrophysics.

Introduction

The Collapsar model originated from efforts to explain long-duration Gamma-ray bursts observed by missions and facilities such as Compton Gamma Ray Observatory, BeppoSAX, Swift, Fermi, and surveys by observatories like Hubble. Early proponents connected it to massive-star collapse pathways studied in the context of Wolf–Rayet star evolution, rotationally driven core dynamics investigated by groups affiliated with Caltech and Princeton, and numerical work at institutions such as Los Alamos National Laboratory and Max Planck Institute for Astrophysics. The model became central to interpreting associations between long bursts and energetic Type Ic supernovae, and to observational programs by teams at European Southern Observatory and Keck Observatory.

Physical Mechanism

In the Collapsar paradigm a massive progenitor’s iron core collapses to form a black hole while surrounding material with sufficient angular momentum forms an accretion disk. General-relativistic effects near the forming black hole, magnetohydrodynamic processes such as the Blandford–Znajek process and magnetic turbulence driven by the magnetorotational instability extract rotational energy to launch relativistic jets. These jets propagate through stellar layers, shock heat material, and produce prompt high-energy emission through internal shocks or magnetic dissipation; subsequent interaction with circumstellar media yields afterglows observed across the electromagnetic spectrum by facilities including VLA, Chandra, and ALMA.

Progenitors and Stellar Evolution

Potential progenitors include massive, rapidly rotating stars that have lost their hydrogen envelopes, commonly identified with Wolf–Rayet stars and stripped-envelope candidates studied in populations at Magellanic Clouds, Andromeda, and local star-forming regions. Binary evolution channels investigated by research groups at Cambridge and Oxford can strip envelopes via mass transfer or common-envelope phases, linking to observations from surveys like the SDSS and catalogs compiled by ESO. Metallicity effects inferred from work associated with Keck Observatory and VLT influence stellar winds and angular-momentum retention; low-metallicity environments such as those in dwarf galaxies cataloged by SDSS surveys favor collapsar conditions. Stellar-evolution models developed at institutions like Monash University and UCSC incorporate rotation, magnetic braking, and mass loss to predict core structures conducive to black-hole formation.

Observable Signatures

Observable signatures attributed to collapsars include long-duration Gamma-ray burst prompt emission, energetic broad-lined Type Ic supernovae often termed hypernovae, and multiwavelength afterglows. Temporal and spectral properties recorded by Fermi and Swift correlate with late-time supernova light curves observed by Hubble, Keck Observatory, and ground-based telescopes in follow-up campaigns coordinated with teams at ESO. Host-galaxy demographics link to studies by SDSS, indicating star-forming, low-metallicity environments found in surveys by Pan-STARRS and GALEX. Polarization measurements from facilities such as Subaru Telescope and modeling efforts at Max Planck Institute for Astrophysics constrain jet geometry and magnetic-field structure, while high-energy neutrino searches by IceCube and gravitational-wave detectors like LIGO and VIRGO probe multimessenger aspects.

Numerical Simulations and Theoretical Developments

High-resolution simulations of collapsar dynamics employ general-relativistic magnetohydrodynamics codes developed at centers including Princeton, Caltech, and Max Planck Institute for Astrophysics. These studies implement microphysics such as neutrino transport and nuclear equations of state informed by laboratory constraints from CERN experiments and theoretical work by groups at Lawrence Livermore National Laboratory. Magnetically driven jet-launching scenarios draw on models like the Blandford–Znajek process and the magnetorotational instability; neutrino-annihilation models compare with magnetically mediated energy extraction in simulations produced at Oak Ridge National Laboratory and NAOJ. Advances in computational infrastructure at institutions such as National Center for Supercomputing Applications and collaborations with projects like Einstein Toolkit enable longer-term, multi-dimensional modeling that connects to analytical work by theorists associated with Princeton and Caltech.

Implications for Gamma-Ray Bursts and Supernovae

If realized in nature, the collapsar channel accounts for a subset of long-duration Gamma-ray bursts and associates those bursts with energetic, stripped-envelope supernovae observed as broad-lined Type Ic events. This linkage informs cosmic-ray acceleration hypotheses investigated by researchers at CERN and Max Planck Institute for Physics, and it constrains rates used in population studies by teams at Harvard–Smithsonian and STScI. The model’s predictions about host environments, metallicity dependence, and jet energetics continue to guide observational campaigns by Fermi, Swift, and ground-based observatories including Keck Observatory and ESO, and they intersect with multimessenger searches conducted by LIGO, VIRGO, and IceCube.

Category:Astrophysics