Growth Of Intermediate Mass Black Holes Research Articles

Merger-driven Growth of Intermediate-mass Black Holes: Constraints from Hubble Space Telescope Imaging of Hyper-luminous X-Ray Sources

Hyper-luminous X-ray sources (HLXs) are extragalactic off-nuclear X-ray sources with luminosities exceeding the theoretical limit for accretion onto stellar-mass compact objects. Many HLXs may represent intermediate-mass black holes (IMBHs) deposited in galaxy halos through mergers, and the properties of the stellar cores surrounding HLXs provide powerful constraints on this scenario. Therefore, we have systematically built the largest sample of HLX candidates with archival Hubble Space Telescope (HST) imaging (24) for the first uniform population study of HLX stellar cores down to low masses. Based on their host galaxy redshifts, at least 21 (88%) have stellar core masses ≥ 107 M ⊙ and hence are consistent with accretion onto massive black holes from external galaxies. In 50% of the sample, the HST imaging reveals features connecting the HLXs with their host galaxies, strongly suggesting against the background/foreground contaminant possibility in these cases. Assuming a mass scaling relation for active galactic nuclei and accounting for an estimated contamination fraction of 29%, up to ∼60% of our sample may be associated with IMBHs. Similar to previously known HLXs, the X-ray luminosities are systematically elevated relative to their stellar core masses, possibly from merger-driven accretion rate enhancements. The least massive stellar cores are preferentially found at larger nuclear offsets and are more likely to remain wandering in their host galaxy halos. The HLX galaxy occupation fraction is ∼ 10−2 and has a strong inverse mass dependence. Up to three of the HLX candidates (12%) are potentially consistent with formation within globular clusters or with exceptionally luminous X-ray binaries.

Mocca-survey Database I: Binary black hole mergers from globular clusters with intermediate mass black holes

ABSTRACT The dynamical formation of black hole binaries in globular clusters that merge due to gravitational waves occurs more frequently in higher stellar density. Meanwhile, the probability to form intermediate mass black holes (IMBHs) also increases with the density. To explore the impact of the formation and growth of IMBHs on the population of stellar mass black hole binaries from globular clusters, we analyse the existing large survey of Monte Carlo globular cluster simulation data (mocca-survey Database I). We show that the number of binary black hole mergers agrees with the prediction based on clusters’ initial properties when the IMBH mass is not massive enough or the IMBH seed forms at a later time. However, binary black hole formation and subsequent merger events are significantly reduced compared to the prediction when the present-day IMBH mass is more massive than ${\sim}10^4\, \rm M_{\odot }$ or the present-day IMBH mass exceeds about 1 per cent of cluster’s initial total mass. By examining the maximum black hole mass in the system at the moment of black hole binary escaping, we find that ∼90 per cent of the merging binary black holes escape before the formation and growth of the IMBH. Furthermore, large fraction of stellar mass black holes are merged into the IMBH or escape as single black holes from globular clusters in cases of massive IMBHs, which can lead to the significant underpopulation of binary black holes merging with gravitational waves by a factor of 2 depending on the clusters’ initial distributions.

Dusty Gas Accretion onto Massive Black Holes and Infrared Diagnosis of the Eddington Ratio

Abstract Evidence for dust around supermassive black holes (SMBHs) in the early universe is strongly suggested by recent observations. However, the accretion mechanism of SMBHs in dusty gas is not well understood yet. We investigate the growth of intermediate-mass black holes (IMBHs) of in dusty clouds by using one-dimensional radiative-hydrodynamics simulations. We find that the accretion of dusty gas onto IMBHs proceeds gently with small fluctuations of the accretion rate, whereas that of pristine gas causes more violent periodic bursts. At dust-to-gas mass ratios similar to the solar neighborhood, the time-averaged luminosity becomes smaller than that for primordial gas by one order of magnitude and the time-averaged Eddington ratio ranges from to in clouds with initial gas densities of . Our calculations show that the effect of dust opacity alone is secondary compared to the radiation pressure on dust in regulating the BH growth. We also derive spectral energy distributions at IR bands by calculating dust thermal emission and show that the flux ratio between and is closely related to the Eddington ratio. Thermal emission from hot dust near the BH dominates only during the phase of high accretion, producing higher flux density at . Therefore, we suggest that a combination of mid-IR observations by the James Webb Space Telescope and far-IR observations by ALMA or Spitzer can be used to estimate the Eddington ratio of massive BHs. We also extend our simple modeling to SMBHs of and show that ALMA can detect SMBHs of at .

Cosmic reionization of hydrogen and helium: contribution from both mini-quasars and stars

Observations on the high-redshift galaxies at $z>6$ imply that their ionizing emissivity is unable to fully reionize the Universe at $z\sim 6$. Either a high escape fraction of ionizing photons from these galaxies or a large population of faint galaxies below the detection limit are required. However, these requirements are somewhat in tension with present observations. In this work, we explored the combined contribution of mini-quasars and stars to the reionization of cosmic hydrogen and helium. Our model is roughly consistent with: (1) the low escape fractions of ionizing photons from the observed galaxies, (2) the optical depth of Cosmic Microwave Background (CMB) measured by the WMAP-7, and (3) the redshift of the end of hydrogen and helium reionization at $z\approx 6$ and $z\approx 3$, respectively. Neither an extremely high escape fraction nor a large population of fainter galaxies is required in this scenario. In our most optimistic model, more than $\sim20\%$ of the cosmic helium is reionized by $z\sim6$, and the ionized fraction of cosmic helium rapidly climbs to more than $50\%$ by $z\sim5$. These results may imply that better measurements of helium reionization, especially at high redshifts, could be helpful in constraining the growth of intermediate-mass black holes (IMBHs) in the early Universe, which would shed some light on the puzzles concerning the formation of supermassive black holes (SMBHs).

Simulating the growth of intermediate-mass black holes

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.

Gamma rays from dark matter minispikes in the Andromeda Galaxy M31

The existence of a population of wandering intermediate mass black holes (IMBHs) is a generic prediction of scenarios that seek to explain the formation of supermassive black holes in terms of growth from massive seeds. The growth of IMBHs may lead to the formation of DM overdensities called ''mini-spikes,'' recently proposed as ideal targets for indirect DM searches. Current ground-based gamma-ray experiments, however, cannot search for these objects due to their limited field of view, and it might be challenging to discriminate mini-spikes in the Milky Way from the many astrophysical sources that GLAST is expected to observe. We show here that gamma-ray experiments can effectively search for IMBHs in the nearby Andromeda Galaxy (also known as M31), where mini-spikes would appear as a distribution of point-sources, isotropically distributed in a {approx_equal}3 deg. circle around the galactic center. For a neutralinolike DM candidate with a mass m{sub {chi}}=150 GeV, up to 20 sources would be detected with GLAST (at 5{sigma}, in 2 months). With air Cherenkov telescopes such as MAGIC and VERITAS, up to 10 sources might be detected, provided that the mass of neutralino is in the TeV range or above.

Three‐Body Dynamics with Gravitational Wave Emission

We present numerical three-body experiments that include the effects of gravitational radiation reaction by using equations of motion that include the 2.5-order post-Newtonian force terms, which are the leading order terms of energy loss from gravitational waves. We simulate binary-single interactions and show that close approach cross sections for three 1 solar mass objects are unchanged from the purely Newtonian dynamics except for close approaches smaller than 1.0e-5 times the initial semimajor axis of the binary. We also present cross sections for mergers resulting from gravitational radiation during three-body encounters for a range of binary semimajor axes and mass ratios including those of interest for intermediate-mass black holes (IMBHs). Building on previous work, we simulate sequences of high-mass-ratio three-body encounters that include the effects of gravitational radiation. The simulations show that the binaries merge with extremely high eccentricity such that when the gravitational waves are detectable by LISA, most of the binaries will have eccentricities e > 0.9 though all will have circularized by the time they are detectable by LIGO. We also investigate the implications for the formation and growth of IMBHs and find that the inclusion of gravitational waves during the encounter results in roughly half as many black holes ejected from the host cluster for each black hole accreted onto the growing IMBH.