Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEffect of mass loss due to stellar winds on the formation of supermassive black hole seeds in dense nuclear star clusters
110
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The observations of high redshifts quasars at $zgtrsim 6$ have revealed that supermassive black holes (SMBHs) of mass $sim 10^9,mathrm{M_{odot}}$ were already in place within the first $sim$ Gyr after the Big Bang. Supermassive stars (SMSs) with masses $10^{3-5},mathrm{M_{odot}}$ are potential seeds for these observed SMBHs. A possible formation channel of these SMSs is the interplay of gas accretion and runaway stellar collisions inside dense nuclear star clusters (NSCs). However, mass loss due to stellar winds could be an important limitation for the formation of the SMSs and affect the final mass. In this paper, we study the effect of mass loss driven by stellar winds on the formation and evolution of SMSs in dense NSCs using idealised N-body simulations. Considering different accretion scenarios, we have studied the effect of the mass loss rates over a wide range of metallicities $Z_ast=[.001-1]mathrm{Z_{odot}}$ and Eddington factors $f_{rm Edd}=L_ast/L_{mathrm{Edd}}=0.5,0.7,,&, 0.9$. For a high accretion rate of $10^{-4},mathrm{M_{odot}yr^{-1}}$, SMSs with masses $gtrsim 10^3MSun$ could be formed even in a high metallicity environment. For a lower accretion rate of $10^{-5},mathrm{M_{odot}yr^{-1}}$, SMSs of masses $sim 10^{3-4},mathrm{M_{odot}}$ can be formed for all adopted values of $Z_ast$ and $f_{rm Edd}$, except for $Z_ast=mathrm{Z_{odot}}$ and $f_{rm Edd}=0.7$ or 0.9. For Eddington accretion, SMSs of masses $sim 10^3,mathrm{M_{odot}}$ can be formed in low metallicity environments with $Z_astlesssim 0.01mathrm{Z_{odot}}$. The most massive SMSs of masses $sim 10^5,mathrm{M_{odot}}$ can be formed for Bondi-Hoyle accretion in environments with $Z_ast lesssim 0.5mathrm{Z_{odot}}$.
rate research
Read More
More than two hundred supermassive black holes (SMBHs) of masses $gtrsim 10^9,mathrm{M_{odot}}$ have been discovered at $z gtrsim 6$. One promising pathway for the formation of SMBHs is through the collapse of supermassive stars (SMSs) with masses $sim 10^{3-5},mathrm{M_{odot}}$ into seed black holes which could grow upto few times $10^9,mathrm{M_{odot}}$ SMBHs observed at $zsim 7$. In this paper, we explore how SMSs with masses $sim 10^{3-5},mathrm{M_{odot}}$ could be formed via gas accretion and runaway stellar collisions in high-redshift, metal-poor nuclear star clusters (NSCs) using idealised N-body simulations. We explore physically motivated accretion scenarios, e.g. Bondi-Hoyle-Lyttleton accretion and Eddington accretion, as well as simplified scenarios such as constant accretions. While gas is present, the accretion timescale remains considerably shorter than the timescale for collisions with the most massive object (MMO). However, overall the timescale for collisions between any two stars in the cluster can become comparable or shorter than the accretion timescale, hence collisions still play a crucial role in determining the final mass of the SMSs. We find that the problem is highly sensitive to the initial conditions and our assumed recipe for the accretion, due to the highly chaotic nature of the problem. The key variables that determine the mass growth mechanism are the mass of the MMO and the gas reservoir that is available for the accretion. Depending on different conditions, SMSs of masses $sim10^{3-5} ,mathrm{M_{odot}}$ can form for all three accretion scenarios considered in this work.
Quiescent galaxies with little or no ongoing star formation dominate the galaxy population above $M_{*}sim 2 times 10^{10}~M_{odot}$, where their numbers have increased by a factor of $sim25$ since $zsim2$. Once star formation is initially shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole, an unknown mechanism must remove or heat subsequently accreted gas from stellar mass loss or mergers that would otherwise cool to form stars. Energy output from a black hole accreting at a low rate has been proposed, but observational evidence for this in the form of expanding hot gas shells is indirect and limited to radio galaxies at the centers of clusters, which are too rare to explain the vast majority of the quiescent population. Here we report bisymmetric emission features co-aligned with strong ionized gas velocity gradients from which we infer the presence of centrally-driven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxies are surprisingly common, accounting for as much as $10%$ of the population at $M_* sim 2 times 10^{10}~ M_{odot}$. In a prototypical example, we calculate that the energy input from the galaxys low-level active nucleus is capable of driving the observed wind, which contains sufficient mechanical energy to heat ambient, cooler gas (also detected) and thereby suppress star formation.
Close encounters and physical collisions between stars in young dense clusters may lead to the formation of very massive stars and black holes via runaway merging. We examine critically some details of this process, using N-body simulations and simple analytical estimates to place limits on the cluster parameters for which it expected to occur. For small clusters, the mass of the runaway is effectively limited by the total number of high-mass stars in the system. For sufficiently dense larger clusters, the runaway mass is determined by the fraction of stars that can mass segregate to the cluster core while still on the main sequence. The result is in the range commonly cited for intermediate-mass black holes, such as that recently reported in the Galactic center.
Supermassive black holes reside in the nuclei of most galaxies. Accurately determining their mass is key to understand how the population evolves over time and how the black holes relate to their host galaxies. Beyond the local universe, the mass is commonly estimated assuming virialized motion of gas in the close vicinity to the active black holes, traced through broad emission lines. However, this procedure has uncertainties associated with the unknown distribution of the gas clouds. Here we show that the comparison of black hole masses derived from the properties of the central accretion disc with the virial mass estimate provides a correcting factor, for the virial mass estimations, that is inversely proportional to the observed width of the broad emission lines. Our results suggest that line-of-sight inclination of gas in a planar distribution can account for this effect. However, radiation pressure effects on the distribution of gas can also reproduce our findings. Regardless of the physical origin, our findings contribute to mitigate the uncertainties in current black hole mass estimations and, in turn, will help to further understand the evolution of distant supermassive black holes and their host galaxies.
Current theoretical models predict a mass gap with a dearth of stellar black holes (BHs) between roughly $50,M_odot$ and $100,M_odot$, while, above the range accessible through massive star evolution, intermediate-mass BHs (IMBHs) still remain elusive. Repeated mergers of binary BHs, detectable via gravitational wave emission with the current LIGO/Virgo/Kagra interferometers and future detectors such as LISA or the Einstein Telescope, can form both mass-gap BHs and IMBHs. Here we explore the possibility that mass-gap BHs and IMBHs are born as a result of successive BH mergers in dense star clusters. In particular, nuclear star clusters at the centers of galaxies have deep enough potential wells to retain most of the BH merger products after they receive significant recoil kicks due to anisotropic emission of gravitational radiation. We show that a massive stellar BH seed can easily grow to $sim 10^3 - 10^4,M_odot$ as a result of repeated mergers with other smaller BHs. We find that lowering the cluster metallicity leads to larger final BH masses. We also show that the growing BH spin tends to decrease in magnitude with the number of mergers, so that a negative correlation exists between final mass and spin of the resulting IMBHs. Assumptions about the birth spins of stellar BHs affect our results significantly, with low birth spins leading to the production of a larger population of massive BHs.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
