Article

# Relativistic collapse and explosion of rotating supermassive stars with thermonuclear effects

(Impact Factor: 6.28). 08/2011; 749(1). DOI: 10.1088/0004-637X/749/1/37
Source: arXiv

ABSTRACT We present results of general relativistic simulations of collapsing
supermassive stars with and without rotation using the two-dimensional general
relativistic numerical code Nada, which solves the Einstein equations written
in the BSSN formalism and the general relativistic hydrodynamics equations with
high resolution shock capturing schemes. These numerical simulations use an
equation of state which includes effects of gas pressure, and in a tabulated
form those associated with radiation and the electron-positron pairs. We also
take into account the effect of thermonuclear energy released by hydrogen and
helium burning. We find that objects with a mass of 5x10^{5} solar mass and an
initial metallicity greater than Z_{CNO}~0.007 do explode if non-rotating,
while the threshold metallicity for an explosion is reduced to Z_{CNO}~0.001
for objects uniformly rotating. The critical initial metallicity for a
thermonuclear explosion increases for stars with mass ~10^{6} solar mass. For
those stars that do not explode we follow the evolution beyond the phase of
black hole formation. We compute the neutrino energy loss rates due to several
processes that may be relevant during the gravitational collapse of these
objects. The peak luminosities of neutrinos and antineutrinos of all flavors
for models collapsing to a BH are ~10^{55} erg/s. The total radiated energy in
neutrinos varies between ~10^{56} ergs for models collapsing to a BH, and
~10^{45}-10^{46} ergs for models exploding.

0 Followers
·
76 Views
• Source
##### Article: Simulating the growth of Intermediate Mass Black Holes
[Hide abstract]
ABSTRACT: Theoretical models predict that a population of Intermediate Mass Black Holes (IMBHs) of mass $M_\bullet \approx 10^{4-5} \, \mathrm{M_{\odot}}$ might form at high ($z > 10$) redshift by different processes. Such objects would represent the seeds out of which $z > 6$ Super-Massive Black Holes (SMBHs) grow. We numerically investigate the radiation-hydrodynamic evolution governing the growth of such seeds via accretion of primordial gas within their parent dark matter halo of virial temperature $T_{vir} \sim 10^4 \, \mathrm{K}$. We find that the accretion onto a Direct Collapse Black Hole (DCBH) of initial mass $M_0=10^5 \, \mathrm{M_{\odot}}$ occurs at an average rate $\dot{M}_{\bullet} \simeq 1.35 \, \dot{M}_{Edd} \simeq 0.1 \, \mathrm{M_{\odot} \, yr^{-1}}$, is intermittent (duty-cycle $< 50\%$) and lasts $\approx 142 \, \mathrm{Myr}$; the system emits on average at super-Eddington luminosities, progressively becoming more luminous as the density of the inner mass shells, directly feeding the central object, increases. Finally, when $\approx 90\%$ of the gas mass has been accreted (in spite of an average super-Eddington emission) onto the black hole, whose final mass is $\sim 7 \times 10^6 \, \mathrm{M_{\odot}}$, the remaining gas is ejected from the halo due to a powerful radiation burst releasing a peak luminosity $L_{peak}\sim 3\times 10^{45} \, \mathrm{erg \, s^{-1}}$. The IMBH is Compton-thick during most of the evolution, reaching a column density $N_H \sim 10^{25} \, \mathrm{cm^{-2}}$ in the late stages of the simulation. We briefly discuss the observational implications of the model.
Monthly Notices of the Royal Astronomical Society 01/2015; 448(1). DOI:10.1093/mnras/stv018 · 5.23 Impact Factor
• Source
##### Article: Dark Stars: A Review
[Hide abstract]
ABSTRACT: Dark Stars (DS) are stellar objects made (almost entirely) of ordinary atomic material but powered by the heat from Dark Matter (DM) annihilation (rather than by fusion). Weakly Interacting Massive Particles (WIMPs), among the best candidates for DM, can be their own antimatter and can accumulate inside the star, with their annihilation products thermalizing with and heating the DS. The resulting DSs are in hydrostatic and thermal equilibrium. The first phase of stellar evolution in the history of the Universe may have been dark stars. Though DM constituted only $<0.1\%$ of the mass of the star, this amount was sufficient to power the star for millions to billions of years. Depending on their DM environment, early DSs can become very massive ($>10^6 M_\odot$), very bright ($>10^9 L_\odot$), and potentially detectable with the James Webb Space Telescope (JWST). Once the DM runs out and the dark star dies, it may collapse to a black hole; thus DSs can provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses DSs existing today but focuses on the early generation of dark stars.
• Source
##### Article: Initial mass function of intermediate mass black hole seeds
[Hide abstract]
ABSTRACT: We study the Initial Mass Function (IMF) and host halo properties of Intermediate Mass Black Holes (IMBH, 10^{4-6} Msun) formed inside metal-free, UV illuminated atomic cooling haloes (virial temperature T_vir > 10^4 K) either via the direct collapse of the gas or via an intermediate Super Massive Star (SMS) stage. We achieve this goal in three steps: (a) we derive the gas accretion rate for a proto-SMS to undergo General Relativity instability and produce a direct collapse black hole (DCBH) or to enter the ZAMS and later collapse into a IMBH; (b) we use merger-tree simulations to select atomic cooling halos in which either a DCBH or SMS can form and grow, accounting for metal enrichment and major mergers that halt the growth of the proto-SMS by gas fragmentation. We derive the properties of the host halos and the mass distribution of black holes at this stage, and dub it the "Birth Mass Function"; (c) we follow the further growth of the DCBH due to accretion of leftover gas in the parent halo and compute the final IMBH mass.We consider two extreme cases in which minihalos (T_vir < 10^4 K) can (fertile) or cannot (sterile) form stars and pollute their gas leading to a different IMBH IMF. In the (fiducial) fertile case the IMF is bimodal extending over a broad range of masses, M= (0.5-20)x10^5 Msun, and the DCBH accretion phase lasts from 10 to 100 Myr. If minihalos are sterile, the IMF spans the narrower mass range M= (1-2.8)x10^6 Msun, and the DCBH accretion phase is more extended (70-120 Myr). We conclude that a good seeding prescription is to populate halos (a) of mass 7.5 < log (M_h/Msun) < 8, (b) in the redshift range 8 < z < 17, (c) with IMBH in the mass range 4.75 < log (M_BH/Msun) < 6.25.
Monthly Notices of the Royal Astronomical Society 06/2014; 443(3). DOI:10.1093/mnras/stu1280 · 5.23 Impact Factor