اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدLoss cone refilling by flyby encounters--A numerical study of massive black holes in galactic centres
51
0
0.0
(
0
)
تأليف
Mimi Zhang
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
A gap in phase-space, the loss cone (LC), is opened up by a supermassive black hole (MBH) as it disrupts or accretes stars in a galactic centre. If a star enters the LC then, depending on its properties, its interaction with the MBH will either generate a luminous electromagnetic flare or give rise to gravitational radiation, both of which are expected to have directly observable consequences. A thorough understanding of loss-cone refilling mechanisms is important for the prediction of astrophysical quantities, such as rates of tidal disrupting main-sequence stars, rates of capturing compact stellar remnants and timescales of merging binary MBHs. In this thesis, we use N-body simulations to investigate how noise from accreted satellites and other substructures in a galaxys halo can affect the LC refilling rate. Any N-body model suffers from Poisson noise which is similar to, but much stronger than, the two-body diffusion occurring in real galaxies. To lessen this spurious Poisson noise, we apply the idea of importance sampling to develop a new scheme for constructing N-body realizations of a galaxy model, in which interesting regions of phase-space are sampled by many low-mass particles. We use multimass N-body models of galaxies with centrally-embedded MBHs to study the effects of satellite flybys on LC refilling rates. We find that although the flux of stars into the initially emptied LC is enhanced, but the fuelling rate averaged over the entire subhalos is increased by only a factor 3 over the rate one expects from the Poisson noise due the discreteness of the stellar distribution.
قيم البحث
اقرأ أيضاً
The origin of supermassive black holes (SMBHs) that inhabit the centers of massive galaxies is largely unconstrained. Remnants from supermassive stars (SMSs) with masses around 10,000 solar masses provide the ideal seed candidates, known as direct co
llapse black holes. However, their very existence and formation environment in the early Universe are still under debate, with their supposed rarity further exacerbating the problem of modeling their ab-initio formation. SMS models have shown that rapid collapse, with an infall rate above a critical value, in metal-free haloes is a requirement for the formation of a proto-stellar core which will then form an SMS. Using a radiation hydrodynamics simulation of early galaxy formation, we show the natural emergence of metal-free haloes both massive enough, and with sufficiently high infall rates, to form an SMS. We find that haloes that are exposed to both a Lyman-Werner intensity of J_LW ~ 3 J_21 and that undergo at least one period of rapid growth early in their evolution are ideal cradles for SMS formation. This rapid growth induces substantial dynamical heating, amplifying the existing Lyman-Werner suppression originating from a group of young galaxies 20 kiloparsecs away. Our results strongly indicate that structure formation dynamics, rather than a critical Lyman-Werner (LW) flux, may be the main driver of massive black hole formation in the early Universe. We find that massive black hole seeds may be much more common in overdense regions of the early Universe than previously considered with a comoving number density up to 10^-3 Mpc^-3.
If supermassive black holes in centres of galaxies form by merging of black-hole remnants of massive Population III stars, then there should be a few black holes of mass one or two orders of magnitude smaller than that of the central ones, orbiting a
round the centre of a typical galaxy. These black holes constitute a weak perturbation in the gravitational potential, which can generate wave phenomena in gas within a disc close to the centre of the galaxy. Here we show that a single orbiting black hole generates a three-arm spiral pattern in the central gaseous disc. The density excess in the spiral arms in the disc reaches values of 3-12% when the orbiting black hole is about ten times less massive than the central black hole. Therefore the observed density pattern in gas can be used as a signature in detecting the most massive orbiting black holes.
Direct numerical integrations of the two-dimensional Fokker-Planck equation are carried out for compact objects orbiting a supermassive black hole (SBH) at the center of a galaxy. As in Papers I-III, the diffusion coefficients incorporate the effects
of the lowest-order post-Newtonian corrections to the equations of motion. In addition, terms describing the loss of orbital energy and angular momentum due to the 5/2-order post-Newtonian terms are included. In the steady state, captures are found to occur in two regimes that are clearly differentiated in terms of energy, or semimajor axis; these two regimes are naturally characterized as plunges (low binding energy) and EMRIs, or extreme-mass-ratio inspirals (high binding energy). The capture rate, and the distribution of orbital elements of the captured objects, are presented for two steady-state models based on the Milky Way: one with a relatively high density of remnants and one with a lower density. In both models, but particularly in the second, the steady-state energy distribution and the distribution of orbital elements of the captured objects are substantially different than if the Bahcall-Wolf energy distribution were assumed. The ability of classical relaxation to soften the blocking effects of the Schwarzschild barrier is quantified.These results, together with those of Papers I-III, suggest that a Fokker-Planck description can adequately represent the dynamics of collisional loss cones in the relativistic regime.
The dynamics of massive black holes (BHs) in galaxy mergers is a rich field of research that has seen much progress in recent years. In this contribution we briefly review the processes describing the journey of BHs during mergers, from the cosmic co
ntext all the way to when BHs coalesce. If two galaxies each hosting a central BH merge, the BHs would be dragged towards the center of the newly formed galaxy. If/when the holes get sufficiently close, they coalesce via the emission of gravitational waves. How often two BHs are involved in galaxy mergers depends crucially on how many galaxies host BHs and on the galaxy merger history. It is therefore necessary to start with full cosmological models including BH physics and a careful dynamical treatment. After galaxies have merged, however, the BHs still have a long journey until they touch and coalesce. Their dynamical evolution is radically different in gas-rich and gas-poor galaxies, leading to a sort of dichotomy between high-redshift and low-redshift galaxies, and late-type and early-type, typically more massive galaxies.
We investigate the effects of mass loss during the main-sequence (MS) and post-MS phases of massive star evolution on black hole (BH) birth masses. We compute solar metallicity Geneva stellar evolution models of an 85 $M_{odot}$ star with mass-loss r
ate ($dot{M}$) prescriptions for MS and post-MS phases and analyze under which conditions such models could lead to very massive BHs. Based on the observational constraints for $dot{M}$ of luminous stars, we discuss two possible scenarios that could produce massive BHs at high metallicity. First, if a massive BH progenitor evolves from the observed population of massive MS stars known as WNh stars, we show that its average post-MS mass-loss rate has to be less than $1,times10^{-5},M_{odot}$/yr. However, this is lower than the typical observed mass-loss rates of luminous blue variables (LBV). Second, a massive BH progenitor could evolve from a yet undetected population of $80-85$ $M_{odot}$ stars with strong surface magnetic fields, which could quench mass loss during the evolution. In this case, the average mass-loss rate during the post-MS LBV phase has to be less than $5,times10^{-5},M_{odot}$/yr to produce 70 $M_{odot}$ BHs. We suggest that LBVs that explode as SNe have large envelopes and small cores that could be prone to explosion, possibly evolving from binary interaction (either mergers or mass gainers that do not fully mix). Conversely, LBVs that directly collapse to BHs could have evolve from massive single stars or binary-star mergers that fully mix, possessing large cores that would favor BH formation.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
