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TOPIC: Supermassive Black Holes


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Title: Is there a maximum mass for black holes in galactic nuclei?
Author: Kohei Inayoshi, Zoltan Haiman

The largest observed supermassive black holes (SMBHs) have a mass of M_BH ~ 10^{10} M_sun, nearly independent of redshift, from the local (z~0) to the early (z>6) Universe. We suggest that the growth of SMBHs above a few 10^{10} M_sun is prevented by small-scale accretion physics, independent of the properties of their host galaxies or of cosmology. Growing more massive BHs requires a gas supply rate from galactic scales onto a nuclear region as high as >10^3 M_sun/yr. At such a high accretion rate, most of the gas converts to stars at large radii (~10-100 pc), well before reaching the BH. We adopt a simple model (Thompson et al. 2005) for a star-forming accretion disk, and find that the accretion rate in the sub-pc nuclear region is reduced to the smaller value of at most a few M_sun/yr. This prevents SMBHs from growing above ~10^{11} M_sun in the age of the Universe. Furthermore, once a SMBH reaches a sufficiently high mass, this rate falls below the critical value at which the accretion flow becomes advection dominated. Once this transition occurs, BH feeding can be suppressed by strong outflows and jets from hot gas near the BH. We find that the maximum SMBH mass, given by this transition, is between M_{BH,max} ~ (1-6) * 10^{10} M_sun, depending primarily on the efficiency of angular momentum transfer inside the galactic disk, and not on other properties of the host galaxy.

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Title: Direct Collapse Black Holes Can Launch Gamma-Ray Bursts and Get Fat to Supermassive Black Holes?
Author: Tatsuya Matsumoto, Daisuke Nakauchi, Kunihito Ioka, Alexander Heger, Takashi Nakamura

The existence of black holes (BHs) of mass ~ 10^{9} M_sun at z > 6 is a big puzzle in astrophysics because even optimistic estimates of the accretion time are insufficient for stellar mass BHs of ~ 10 M_sun to grow into such supermassive BHs. A resolution of this puzzle might be the direct collapse of supermassive stars with mass M ~ 10^{5} M_sun into massive seed BHs. We find that if a jet is launched from the accretion disk around the central BH, the jet can break out the star because of the structure of the radiation pressure-dominated envelope. Such ultra-long gamma-ray bursts with duration of ~ 10^{4} - 10^{6} s and flux of 10^{-11} - 10^{-8} erg s^{-1} cm^{-2} could be detectable by Swift. We estimate an event rate of < 1yr^{-1}. The total explosion energy is > 10^{55} - 10^{56} erg. The resulting negative feedback delays the growth of the remnant BH by about 70 Myr or evacuates the host galaxy completely.

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Direct collapse black holes
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Title: New constraints on direct collapse black hole formation in the early Universe
Author: Bhaskar Agarwal, Britton Smith, Simon Glover, Priyamvada Natarajan, Sadegh Khochfar

Direct collapse black holes (DCBH) have been proposed as a solution to the challenge of assembling supermassive black holes by z>6 to explain the bright quasars observed at this epoch. The formation of a DCBH seed with MBH~104-5 solar masses, requires a pristine atomic-cooling halo to be illuminated by an external radiation field that is sufficiently strong to entirely suppress H2 cooling in the halo. Many previous studies have attempted to constrain the critical specific intensity that is likely required to suppress H2 cooling, denoted as Jcrit. However, these studies have typically assumed that the incident external radiation field can be modeled with a black-body spectrum. Under this assumption, it is possible to derive a {unique} value for Jcrit that depends only on the temperature of the black-body. In this study we consider a more realistic spectral energy distribution (SED) for the external source of radiation that depends entirely on its star formation history and age. The rate of destruction of the species responsible for suppressing molecular hydrogen cooling depends on the detailed shape of the SED. Therefore the value of Jcrit is tied to the shape of the incident SED of the nearest star-forming protogalaxy. We fit a parametric form to the rates of destruction of H2 and H- that permit direct collapse. Owing to this, we find that Jcrit is not a fixed threshold but can lie anywhere in the range Jcrit~0.5--103, depending on the details of the source stellar population, and its distance from the atomic cooling halo.

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Furious Black Hole Winds

NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) and ESA's (European Space Agency) XMM-Newton telescope are showing that fierce winds from a supermassive black hole blow outward in all directions -- a phenomenon that had been suspected, but difficult to prove until now.
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Title: Polarisation in lines - a new method for measuring black hole masses in active galaxies
Author: Victor L. Afanasiev, Luka C. Popovic

Measuring of the masses of galactic supermassive black holes (SMBHs) is an important task, since they correlate with the host galaxy properties and play an important role in evolution of galaxies. Here we present a new method for measuring of SMBH masses using the polarisation of the broad lines emitted from active galactic nuclei (AGNs). We performed spectropolarometric observations of 9 AGNs and find that this method gives measured masses which are in a good agreement with reverberation measurements. An advantage of this method is that it can be used to measure the masses of SMBHs in a consistent way at different cosmological epochs.

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NASA's WISE Findings Poke Hole in Black Hole 'Doughnut' Theory

A survey of more than 170,000 supermassive black holes, using NASA's Wide-field Infrared Survey Explorer (WISE), has astronomers reexamining a decades-old theory about the varying appearances of these interstellar objects.
The unified theory of active, supermassive black holes, first developed in the late 1970s, was created to explain why black holes, though similar in nature, can look completely different. Some appear to be shrouded in dust, while others are exposed and easy to see.

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Title: Missing black holes in brightest cluster galaxies as evidence for the occurrence of superkicks in nature
Author: Davide Gerosa, Alberto Sesana

We investigate the consequences of superkicks on the population of supermassive black holes (SMBHs) in the Universe residing in brightest cluster galaxies (BCGs). BCGs are the most massive galaxies in the Universe, sitting at the center of galaxy clusters. There is strong observational evidence that they grew prominently at late times (up to a factor 2-4 in mass from z=1), mainly through mergers with satellite galaxies from the cluster, and they host the most massive SMBHs ever observed, with masses up to ten billion solar masses. Those SMBHs are also expected to grow hierarchically, together with their host galaxies, experiencing a series of mergers with other SMBHs brought in by merging satellites. Because of the asymmetric gravitational wave emission, some net linear momentum is emitted during the last stages of the binary inspiral and the remnant SMBH experiences a kick in the opposite direction. Kicks may be as large as ~5000 Km/s ("superkicks"), pushing the SMBHs out in the cluster outskirts for a time comparable to galaxy-evolution timescales. Therefore, measurements of the SMBH occupation fraction can be used to observationally test the existence of superkicks in nature. Because of their violent merger history, BCGs are the ideal objects to explore this possibility. Series of (super)kicks are expected to take place, increasing the total ejection probability. Moreover, BCGs host the SMBHs with the largest sphere of influence on the surrounding stars, which makes them the easiest targets for SMBH mass measurements. We predict, under a number of plausible assumptions, that superkicks can efficiently eject SMBHs from BCGs, bringing their occupation fraction down to a likely range 0.9 < f < 0:99 in the local Universe. Future thirty-meter-class telescopes like ELT and TMT will be capable of measuring SMBHs in hundreds of BCGs up to z=0.2. A single observational confirmation of a missing nuclear SMBH would provide strong evidence for the occurrence of superkicks in the strong-gravity regime of BH mergers.

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Clouds circling supermassive black holes

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Supermassive black hole weighed using new scale

Researchers have proposed a new means for getting a measure of just how massive supermassive black holes are.
They are known to exist at the centres of most galaxies, but a puzzle remains as to how they affect galaxy evolution.
The approach, published in Nature, infers a black hole's mass from the speed of molecules swirling around it.

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Black holes growing faster than expected

Astronomers from Swinburne University of Technology have discovered how supermassive black holes grow - and it's not what was expected.
For years, scientists had believed that supermassive black holes, located at the centres of galaxies, increased their mass in step with the growth of their host galaxy. However, new observations have revealed a dramatically different behaviour.

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