* Astronomy

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RE: Supermassive Black Holes

Blobrana · L

Ashes from massacred planets hide black holes

Planets and asteroids may be smashing into each other by the thousand around monster black holes. Dust from the collisions could explain why many of these colossal objects, which would otherwise shine brightly as they swallow nearby matter, are hidden from view.
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Title: Are SMBHs shrowded by "Super-Oort" clouds of comets and asteroids?
Authors: Sergei Nayakshin, Sergey Sazonov, Rashid Sunyaev

Recent decade saw a dramatic confirmation that an in situ star formation is possible inside the inner parsec of the Milky Way. Here we suggest that giant planets, solid terrestrial-like planets, comets and asteroids may also form in these environments, and that this may have observational implications for Active Galactic Nuclei (AGN). Like in debris discs around main sequence stars, collisions of large solid objects should initiate strong fragmentation cascades. The smallest particles in such a cascade -- the microscopic dust -- may provide a significant opacity. We put a number of observational and physical constraints on AGN obscuring torii resulting from such fragmentation cascades. We find that torii fed by fragmenting asteroids disappear at both low and high AGN luminosities. At high luminosities, L ~ L_Edd, where L_Edd is the Eddington limit, the AGN radiation pressure blows out the microscopic dust too rapidly. At low luminosities, on the other hand, the AGN discs may avoid gravitational fragmentation into stars and solids. We also note that these fragmentation cascades may be responsible for astrophysically "large" dust particles of approximately micrometer sizes that were postulated by some authors to explain unusual absorption properties of the AGN torii.

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Even Low-Mass Galaxies Can Harbour Supermassive Black Holes

Using the slitless grism on Hubble Space Telescope's Wide Field Camera 3 to probe the distant universe, astronomers have found supermassive black holes growing in surprisingly small galaxies. The findings suggest that central black holes formed at an earlier stage in galaxy evolution. This study is part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and will be published in the Astrophysical Journal.
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Movement of black holes powers the universe's brightest lights, study finds

Whether on their own or orbiting as a pair, black holes don't typically sit still.
Not only do they spin, they can also move laterally across their host galaxy. And according to astrophysicists at Brigham Young University, both types of movement power massive jets of energy known as quasars.
The study, which appears in the current issue of Proceedings of the National Academy of Sciences, is the first to compute what may fuel some of the brightest persistent lights in the universe.
These spectacular jets stream out of galaxies that contain discs of debris and gas, the remnants of stars ripped apart by the force from black holes.
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What Activates a Supermassive Black Hole?
Galaxy collisions not the culprits, even in the jam-packed early Universe

A new study combining data from ESO's Very Large Telescope and ESA's XMM-Newton X-ray space observatory has turned up a surprise. Most of the huge black holes in the centres of galaxies in the past 11 billion years were not turned on by mergers between galaxies, as had been previously thought.
At the heart of most, if not all, large galaxies lurks a supermassive black hole with a mass millions, or sometimes billions, times greater than that of the Sun. In many galaxies, including our own Milky Way, the central black hole is quiet. But in some galaxies, particularly early on in the history of the Universe, the central monster feasts on material that gives off intense radiation as it falls into the black hole.
One unsolved mystery is where the material comes from to activate a sleeping black hole and trigger violent outbursts at a galaxy's centre, so that it then becomes an active galactic nucleus. Up to now, many astronomers thought that most of these active nuclei were turned on when two galaxies merge or when they pass close to each other and the disrupted material becomes fuel for the central black hole. However, new results indicate that this idea may be wrong for many active galaxies.
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Black holes spin faster and faster

Two UK astronomers have found that the giant black holes in the centre of galaxies are on average spinning faster than at any time in the history of the Universe. Dr Alejo Martinez-Sansigre of the University of Portsmouth and Prof. Steve Rawlings of the University of Oxford made the new discovery by using radio, optical and X-ray data. They publish their findings in the journal Monthly Notices of the Royal Astronomical Society.
There is strong evidence that every galaxy has a black hole in its centre. These black holes have masses of between a million and a billion Suns and so are referred to as 'supermassive'. They cannot be seen directly, but material swirls around the black hole in a so-called accretion disk before its final demise. That material can become very hot and emit radiation including X-rays that can be detected by space-based telescopes whilst associated radio emission can be detected by telescopes on the ground.
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Giant Black Holes Revealed in the Nuclei of Merging Galaxies

A Japanese research team has used mid-infrared cameras mounted on the Subaru Telescope as well as on the Gemini South telescope to observe samples of many infrared bright, merging galaxies. Observations revealed that some samples show characteristics of rapid star-formation, while others display the signature of active galactic nuclei that draw their energy from active supermassive black holes deeply buried in their centers.
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Newly Merged Black Hole Eagerly Shreds Stars

A galaxy's core is a busy place, crowded with stars swarming around an enormous black hole. When galaxies collide, it gets even messier as the two black holes spiral toward each other, merging to make an even bigger gravitational monster.
Once it is created, the monster goes on a rampage. The merger kicks the black hole into surrounding stars. There it finds a hearty meal, shredding and swallowing stars at a rapid clip. According to new research by Nick Stone and Avi Loeb (Harvard-Smithsonian Centre for Astrophysics), upcoming sky surveys might offer astronomers a way to catch a gorging black hole "in the act."
Before the merger, as the two black holes whirl around each other, they stir the galactic center like the blade of a blender. Their strong gravity warps space, sending out ripples known as gravitational waves. When the black holes merge, they emit gravitational waves more strongly in one direction. That inequality kicks the black hole in the opposite direction like a rocket engine.
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Title: Supermassive black holes do not correlate with galaxy disks or pseudobulges
Authors: John Kormendy, R. Bender, M. E. Cornell

The masses of supermassive black holes are known to correlate with the properties of the bulge components of their host galaxies. In contrast, they appear not to correlate with galaxy disks. Disk-grown pseudobulges are intermediate in properties between bulges and disks. It has been unclear whether they do or do not correlate with black holes in the same way that bulges do, because too few pseudobulges were classified to provide a clear result. At stake are conclusions about which parts of galaxies coevolve with black holes, possibly by being regulated by energy feedback from black holes. Here we report pseudobulge classifications for galaxies with dynamically detected black holes and combine them with recent measurements of velocity dispersions in the biggest bulgeless galaxies. These data confirm that black holes do not correlate with disks and show that they correlate little or not at all with pseudobulges. We suggest that there are two different modes of black hole feeding. Black holes in bulges grow rapidly to high masses when mergers drive gas infall that feeds quasar-like events. In contrast, small black holes in bulgeless galaxies and galaxies with pseudobulges grow as low-level Seyferts. Growth of the former is driven by global processes, so the biggest black holes coevolve with bulges, but growth of the latter is driven locally and stochastically, and they do not coevolve with disks and pseudobulges.

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