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Black holes - no place left to hide

Very sensitive, wide-field observations with a worldwide network of radio telescopes have uncovered black holes residing in the centre of dust obscured galaxies. In some cases, the amount of dust is so large that even x-rays from the accreting black holes are absorbed in these systems. This is the result of research done by astronomers Chi, Barthel and Garrett from Groningen and Dwingeloo, and is set to appear in an upcoming issue of Astronomy & Astrophysics.
Also in apparently normal galaxies, it seems black holes grow steadily by devouring matter. The bright, exotic radiation, usually the result of these so-called accretion processes, seems to be completely obscured in some galaxies. Only a network of highly sensitive radio telescopes can detect these processes is the conclusion of the Dutch astronomers. The suspicion that the faint radio waves, emitted by many galaxies in the distant early universe is the result of accretion by their black holes, has now been proven.

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Super-massive black hole inflates giant bubble

Like symbiotic species, a galaxy and its central black hole lead intimately connected lives. The details of this relationship still pose many puzzles for astronomers. Some black holes actively accrete matter. Part of this material does not fall into the black hole but is ejected in a narrow stream of particles, travelling at nearly the speed of light. When the stream slows down, it creates a tenuous bubble that can engulf the entire galaxy. Invisible to optical telescopes, the bubble is very prominent at low radio frequencies. The new International LOFAR Telescope - designed and built by ASTRON in an international collaboration - is ideally suited to detect this low frequency emission.
Astronomers have produced one of the best images ever of such a bubble, using LOFAR to detect frequencies from 20 to 160 MHz. 

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Black holes turn up the heat for the Universe

HITS astrophysicists discover a new heating source in cosmological structure formation

So far, astrophysicists thought that super-massive black holes can only influence their immediate surroundings. A collaboration of scientists at the Heidelberg Institute for Theoretical Studies (HITS) and in Canada and the US now discovered that diffuse gas in the universe can absorb luminous gamma-ray emission from black holes, heating it up strongly. This surprising result has important implications for the formation of structures in the universe. The results have just been published in "The Astrophysical Journal" and "Monthly Notices of the Royal Astronomical Society".
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Black Hole Flare Simulation

Credit: NASA, S. Gezari (The Johns Hopkins University), and J. Guillochon (University of California, Santa Cruz)

This computer simulation shows a star being shredded by the gravity of a massive black hole. 

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 Black Hole Caught Red-handed in a Stellar Homicide

Astronomers have gathered the most direct evidence yet of a supermassive black hole shredding a star that wandered too close. NASA's Galaxy Evolution Explorer, a space-based observatory, and the Pan-STARRS1 telescope on the summit of Haleakala in Hawaii were among the first to the scene, helping to identify the stellar remains.
Supermassive black holes, weighing millions to billions times more than the sun, lurk in the centers of most galaxies. These hefty monsters lay quietly until an unsuspecting victim, such as a star, wanders close enough to get ripped apart by their powerful gravitational clutches.

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Astronomers put forward new theory on size of black holes

Astronomers have put forward a new theory about why black holes become so hugely massive - claiming some of them have no 'table manners', and tip their 'food' directly into their mouths, eating more than one course simultaneously.
Researchers from the UK and Australia investigated how some black holes grow so fast that they are billions of times heavier than the sun.
The team from the University of Leicester (UK) and  Monash University in Australia sought to establish how black holes got so big so fast.  Their research is due to published in the Monthly Notices of the Royal Astronomical Society.

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New theory on gas-guzzling black holes

Astronomers from the UK and Australia have put forward a new theory about why black holes become so hugely massive - claiming some of them have no 'table manners', and tip their 'food' directly into their mouths, eating more than one course simultaneously.
The team from the University of Leicester and Monash University in Australia sought to establish how some black holes grow so fast that they are billions of times heavier than the sun.  Their research is due to published in the Monthly Notices of the Royal Astronomical Society.

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Title: Rapid AGN accretion from counter-rotating discs
Authors: Chris Nixon, Andrew King, Daniel Price

Accretion in the nuclei of active galaxies may occur chaotically. This can produce accretion discs which are counter-rotating or strongly misaligned with respect to the spin of the central supermassive black hole (SMBH), or the axis of a close SMBH binary. Accordingly we consider the cancellation of angular momentum in accretion discs with a significant change of plane (tilt) between inner and outer parts. We estimate analytically the maximum accretion rate through such discs and compare this with the results of Smoothed Particle Hydrodynamics (SPH) simulations. These suggest that accretion rates on to supermassive black holes may be larger by factors \gtrsim 100 if the disc is internally tilted in this way rather than planar. This offers a natural way of driving the rapid growth of supermassive black holes, and the coalescence of SMBH binaries.

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Title: Supermassive black hole ancestors
Authors: Andrea Petri, Andrea Ferrara, Ruben Salvaterra

We study a model in which supermassive black holes (SMBHs) can grow by the combined action of gas accretion on heavy seeds and mergers of both heavy (m_s^h=10^5 Msol) and light (m_s^l = 10^2 Msol) seeds. The former result from the direct collapse of gas in T_s^h >1.5x10^4K, H_2-free halos; the latter are the endproduct of a standard H_2-based star formation process. The H_2-free condition is attained by exposing halos to a strong (J_21 > 10^3) Lyman-Werner UV background produced by both accreting BHs and stars, thus establishing a self-regulated growth regime. We find that this condition is met already at z close to 18 in the highly biased regions in which quasars are born. The key parameter allowing the formation of SMBHs by z=6-7 is the fraction of halos that can form heavy seeds: the minimum requirement is that f_heavy>0.001; SMBH as large as 2x10^10 Msol can be obtained when f_heavy approaches unity. Independently of f_heavy, the model produces a high-z stellar bulge-black hole mass relation which is steeper than the local one, implying that SMBHs formed before their bulge was in place. The formation of heavy seeds, allowed by the Lyman-Werner radiative feedback in the quasar-forming environment, is crucial to achieve a fast growth of the SMBH by merger events in the early phases of its evolution, i.e. z>7. The UV photon production is largely dominated by stars in galaxies, i.e. black hole accretion radiation is sub-dominant. Interestingly, we find that the final mass of light BHs and of the SMBH in the quasar is roughly equal by z=6; by the same time only 19% of the initial baryon content has been converted into stars. The SMBH growth is dominated at all epochs z > 7.2 by mergers (exceeding accretion by a factor 2-50); at later times accretion becomes by far the most important growth channel. We finally discuss possible shortcomings of the model.

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Do black holes help stars form?

The centre of just about every galaxy is thought to host a black hole, some with masses of thousands of millions of Suns and consequently strong gravitational pulls that disrupt material around them. They had been thought to hinder the birth of stars, but now an international team of astronomers studying the nearby galaxy Centaurus A has found quite the opposite: a black hole that seems to be helping stars to form. The team, led by Dr Stanislav Shabala of the University of Tasmania, Dr Mark Crockett of the University of Oxford, and Dr Sugata Kaviraj of Imperial College, London, publish their results in the journal Monthly Notices of the Royal Astronomical Society.
Black holes at the centre of galaxies 'switch on' from time to time, driving material around them into outflows that can stretch for millions of light years. The flows plough through galactic gas, compressing, heating and pushing it out of the way. Much of this gas is the raw material from which stars are made, so the outflows significantly affect star formation in the galaxies that host them.

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