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Title: Giant black hole ringings induced by massive gravity
Author: Yves Decanini, Antoine Folacci, Mohamed Ould El Hadj

A distorted black hole radiates gravitational waves in order to settle down in one of the geometries permitted by the no-hair theorem. During that relaxation phase, a characteristic damped ringing is generated. It can be theoretically constructed from the black hole quasinormal frequencies (which govern its oscillating behavior and its decay) and from the associated excitation factors (which determine intrinsically its amplitude) by carefully taking into account the source of the distortion. Here, by considering the Schwarzschild black hole in the framework of massive gravity, we show that the excitation factors have an unexpected strong resonant behavior leading to giant ringings which are, moreover, slowly decaying. Such extraordinary black hole ringings could be observed by the next generations of gravitational wave detectors and allow us to test the various massive gravity theories or their absence could be used to impose strong constraints on the graviton mass.

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Obese black holes outshone stars in earliest galaxies

Obese black holes, not stars, may have lit up the first galaxies and could have grown into the earliest supermassive black holes. A new study suggests that these fatties were numerous and bright enough that we should be able to detect them now, billions of years after they shone.
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NASA Chandra, Spitzer Study Suggests Black Holes Abundant Among The Earliest Stars

By comparing infrared and X-ray background signals across the same stretch of sky, an international team of astronomers has discovered evidence of a significant number of black holes that accompanied the first stars in the universe.
Using data from NASA's Chandra X-ray Observatory and NASA's Spitzer Space Telescope, which observes in the infrared, researchers have concluded one of every five sources contributing to the infrared signal is a black hole.

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Quantum gravity takes singularity out of black holes

Falling into a black hole may not be as final as it seems. Apply a quantum theory of gravity to these bizarre objects and the all-crushing singularity at their core disappears.
In its place is something that looks a lot like an entry point to another universe. Most immediately, that could help resolve the nagging information loss paradox that dogs black holes.
Though no human is likely to fall into a black hole anytime soon, imagining what would happen if they did is a great way to probe some of the biggest mysteries in the universe. Most recently this has led to something known as the black hole firewall paradox - but black holes have long been a source of cosmic puzzles.

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Black Hole inner-disk winds
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Title: Constraints on Compton-thick winds from black hole accretion disks: can we see the inner disk?
Authors: Christopher S. Reynolds (Maryland)

Strong evidence is emerging that winds can be driven from the central regions of accretion disks in both active galactic nuclei (AGN) and Galactic black hole binaries (GBHBs). Direct evidence for highly-ionised, Compton-thin inner-disk winds comes from observations of blueshifted (v~0.05-0.1c) iron-K X-ray absorption lines. However, it has been suggested that the inner regions of black hole accretion disks can also drive Compton-thick winds --- such winds would enshroud the inner disk, preventing us from seeing direct signatures of the accretion disk (i.e. the photospheric thermal emission, or the Doppler/gravitationally broadened iron K-alpha line). Here, we show that, provided the source is sub-Eddington, the well-established wind driving mechanisms fail to launch a Compton-thick wind from the inner disk. For the accelerated region of the wind to be Compton-thick, the momentum carried in the wind must exceed the available photon momentum by a factor of at least 2/lambda, where lambda is the Eddington ratio of the source, ruling out radiative acceleration unless the source is very close to the Eddington limit. Compton-thick winds also carry large mass-fluxes, and a consideration of the connections between the wind and the disk show this to be incompatible with magneto-centrifugal driving. Finally, thermal driving of the wind is ruled out on the basis of the large Compton-radii that typify black hole systems. In the absence of some new acceleration mechanism, we conclude that the inner regions of sub-Eddington accretion disks around black holes are indeed naked.

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World's First Glimpse of Black Hole Launchpad

The current issue of Science Express, the online advance publication of the journal, features a paper by the Event Horizon telescope team - a collaboration which includes Perimeter Associate Faculty member Avery Broderick - that may shed light on the origin of the bright jets given off by some black holes. In a world first, the team has been able to look at a distant black hole and resolve the area where its jets are launched from. This is the first empirical evidence to support the connection between black hole spin and black hole jets that has been long suspected on theoretical grounds.
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Explaining black holes

University researchers have discovered a new property of black holes: their dying tones could reveal the cosmic crash that produced them.
Black holes are regions of space where gravity is so strong that not even light can escape and so isolated black holes are truly dark objects and don't emit any form of radiation.
However, black holes that get deformed, because of other black holes or stars crashing into them, are known to emit a new sort of radiation, called gravitational waves, which Einstein predicted nearly a hundred years ago.

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Title: Tidal effects around higher-dimensional black holes
Authors: Richard Brito, Vitor Cardoso, Paolo Pani

In four-dimensional spacetime, moons around black holes generate low-amplitude tides, and the energy extracted from the hole's rotation is always smaller than the gravitational radiation lost to infinity. Thus, moons orbiting a black hole inspiral and eventually merge. However, it has been conjectured that in higher-dimensional spacetimes orbiting bodies generate much stronger tides, which backreact by tidally accelerating the body outwards. This effect, analogous to the tidal acceleration experienced by the Earth-Moon system, would determine the evolution of the binary. Here, we put this conjecture to the test, by studying matter coupled to a massless scalar field in orbit around a singly-spinning rotating black hole in higher dimensions. We show that in dimensions larger than five the energy extracted from the black hole through superradiance is larger than the energy carried out to infinity. Our numerical results are in excellent agreement with analytic approximations and lend strong support to the conjecture that tidal acceleration is the rule, rather than the exception, in higher dimensions. Superradiance dominates the energy budget and moons "outspiral"; for some particular orbital frequency, the energy extracted at the horizon equals the energy emitted to infinity and "floating orbits" generically occur. We give an interpretation of this phenomenon in terms of the membrane paradigm and of tidal acceleration due to energy dissipation across the horizon.

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How black holes change gear

Black holes are extremely powerful and efficient engines that not only swallow up matter, but also return a lot of energy to the Universe in exchange for the mass they eat. When black holes attract mass they also trigger the release of intense X-ray radiation and power strong jets. But not all black holes do this the same way. This has long baffled astronomers. By studying two active black holes researchers at the SRON Netherlands Institute for Space Research have now gathered evidence that suggests that each black hole can change between two different regimes, like changing the gears of an engine. The team's findings will be published in two papers in the journal Monthly Notices of the Royal Astronomical Society.
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Primordial black holes
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 Earth has little to fear from a black hole attack

We can all rest easy. Small black holes that may be roaming space undetected would leave Earth unscathed if they hit us.
Various models suggest matter may have collapsed into black holes soon after the big bang. The smallest of these so-called primordial black holes would have evaporated through a process called Hawking radiation long ago.
But those weighing a billion tonnes or more could still be around, and many of these black holes would be hard to detect - unless they hit us, says Katherine Mack of the University of Cambridge.

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