Multi-messenger Emission Of Black Hole Hyperaccretion In The Center Of Massive Collapsars

Stars are the most common and important celestial bodies in the universe.The formation and evolution of stars are affected by the environment of the galaxy and also give feedback to the galaxy.The evolution and final outcome of stars are mainly determined by the initial mass and chemical composition of stars,and the final product of the star may be a white dwarf,a neutron star(NS),or a black hole(BH).Massive stars may produce core collapse supernovae(CCSNe)and gamma-ray bursts(GRB s)at the end of their life.These two violent outbursts can have important feedback effects on galaxies.Both supernovae and GRBs can produce rich electromagnetic signals that cover the entire electromagnetic spectrum.In the era of multi-messenger,neutrino and gravitational wave(GW)detection will greatly advance our knowledge and understanding of massive star core collapse,supernovae,GRBs,and compact objects.This paper reviews the research progress of star evolution,supernovae,and GRBs,and introduces my research results.We mainly studied the fallback accretion process of CCSNe and the central engine of GRBs(the BH hyperaccretion system),and calculated their multi-messenger emission.The paper consists of three parts:review part(Chapter 1),working part(Chapter 2-4),summary and future research plan(Chapter 5).The first chapter introduces star evolution,supernovae,and GRBs.We first introduced the evolution and final outcomes of stars.Then the classifications,progenitors,and explosion mechanisms of supernovae are summarized.Finally,we gave a brief introduction of GRBs and presented the leading central engine models of GRBs i.e.,the BH hyperaccretion system.In Chapter 2,we studied the properties of BH hyperaccretion systems in the collapsar scenario.The disk should be in a state of neutrino-dominated accretion flow(NDAF)if the accretion rate is larger than the ignition rate of an ND AF.We calculated the effects of the masses and metallicities of progenitor stars on the time-integrated spectra of electron neutrinos from NDAFs.The peak energies of the calculated spectra are approximately 10-20 MeV.We also investigated the differences in the electron neutrino spectra between NDAF’s and proto-neutron stars(PNSs).Combining with the electromagnetic counterparts and multi-messenger astronomy,one may verify the possible remnants of the collapse of massive stars.Then we investigated the GW emission generated by the anisotropic neutrino emission from NDAFs in the collapsar scenarios.The typical frequency of GWs is～1-100 Hz,and the masses and metallicities of the progenitor stars have slight effects on the GW strains.Moreover,comparisons of the detectable GWs from collapsars,NDAFs,and GRB jets(internal shocks)are displayed.We studied jet propagation in different progenitor stars.For some collapsars,the jets cannot breakout from the star.For a GRB from collapsar,we can constrain the density profile of progenitor by the total energy of the GRB.By combining the electromagnetic counterparts,neutrinos,and GWs,one may constrain the characteristics of collapsars and central BH accretion systems.In Chapter 3,we revisited the numerical simulations on the CCSNe for～20-40 M☉progenitor stars with different initial explosion energies.As a result,the lower explosion energy naturally causes more efficient fallback accretion for low-metallicity progenitors,and then the newborn BHs in the center of the CCSNe can escape from the gap,but NSs cannot easily collapse into BHs in the gap;nevertheless,the final remnants of the solarmetallicity progenitors stick to the gap.If we consider that only drastic CCSNe can be observed and that those with lower explosion energies are universal,the lower mass gap can be reasonably built.The width and depth of the gap are mainly determined by the typical CCSN initial explosion energy and metallicity.One can expect that the future multi-messenger observations of compact objects delineate the shape of the gap,which might constrain the properties of the CCSNe and their progenitors.In Chapter 4,anisotropic neutrinos and GWs from NDAFs in fallback CCSNe are investigated.We performed a series of one-dimensional CCSN simulations with the initial explosion energy in the range of 2-8 B(1B=1051 erg)to investigate the fallback processes.By considering the evolution of the central BH mass and spin in the fallback accretion,we presented the effects of the initial explosion energies,masses,and metallicities of the massive progenitor stars on the spectra of anisotropic MeV neutrinos and the waveform of GWs from NDAFs.These neutrino or GW signals might be detected by operational or future detectors,and the multi-messenger joint detections could constrain the properties of CCSNe and progenitor stars.Finally,we gave a brief summary and outlook.In the future,I have two research goals.First,I will study the diffuse NDAF neutrino background and GW background.Second,I will constrain progenitor properties of different CCSNe by simulations.