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TOPIC: Black Holes


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Stellar-mass black holes
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Title: Black Holes in the Galaxy
Authors: Josep M. Paredes

The most compelling evidences for the existence of stellar-mass black holes have been obtained through observations of X-ray binary systems. The application of classical methods and the development of new techniques have allowed us to increase the number of stellar-mass black holes known. I summarise here the observational signatures of the black holes, such as the mass determination, the event horizon and the spin. I also present some observational results on the Galactic centre black hole.

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RE: Black Holes
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Turbulence responsible for black holes' balancing act
New simulations reveal that turbulence created by jets of material ejected from the disks of the Universes largest black holes is responsible for halting star formation. Evan Scannapieco, an assistant professor in the School of Earth and Space Exploration in the College of Liberal Arts and Sciences at Arizona State University (ASU) and Professor Marcus Brueggen of Jacobs University in Bremen, Germany, present the new model in a paper in the journal Monthly Notices of the Royal Astronomical Society.
We live in a hierarchical Universe where small structures join into larger ones. Earth is a planet in our Solar System, the Solar System resides in the Milky Way Galaxy, and galaxies combine into groups and clusters. Clusters are the largest structures in the Universe, but sadly our knowledge of them is not proportional to their size. Researchers have long known that the gas in the centres of some galaxy clusters is rapidly cooling and condensing, but were puzzled why this condensed gas did not form into stars. Until recently, no model existed that successfully explained how this was possible.
Professor Scannapieco has spent much of his career studying the evolution of galaxies and clusters. There are two types of clusters: cool-core clusters and non-cool core clusters

"There are two types of clusters: cool-core clusters and non-cool core clusters. Non-cool core clusters haven't been around long enough to cool, whereas cool-core clusters are rapidly cooling, although by our standards they are still very hot" - Evan Scannapieco.

Scannapieco is an assistant professor in Arizona State University's School of Earth and Space Exploration in the College of Liberal Arts and Sciences.

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CSIRO produce first 'image' of black hole
Science has for the first time produced an image of what a the enormous black hole in the heart of a neighbouring galaxy looks like.
The monster black hole at the centre of the Centaurus A galaxy is a major source of radio waves. Now we can see what they look like, for the first time.
CSIRO astronomers wanted to see the radio glow, even though radio waves are invisible. So they combined data from radio telescopes and created a single image.

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Astronomers See A New Class of Black Hole
Scientists say X-ray data collected by the European Space Agency's XMM-Newton spacecraft show evidence of a new type of black hole in a galaxy about 290 million light years from Earth. Astronomer Sean Farrell explains what the discovery might tell us about galaxy evolution.

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Some of the biggest black holes in the nearby Universe may be much larger than previously thought.
A reassessment of the monster hole at the core of the M87 galaxy suggests it could have 6.4 billion times the mass of our own Sun.
This result is two to three times the estimates from earlier studies.

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A supermassive black hole lurking deep in the heart of a distant active galaxy has been probed more closely than ever before by a team of astronomers that includes Penn State Professor of Astronomy Niel Brandt. Using new X-ray data from the European Space Agency's XMM-Newton satellite, the team observed the galaxy -- known as 1H0707-495 -- for four 48-hour-long periods, revealing the innermost depths of the galaxy.

"We now can start to map out the region immediately around the black hole" - Andrew Fabian of the University of Cambridge, who headed the observations and analysis.

A research paper describing the team's discoveries will be published on May 28 in the journal Nature.


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Looking inside a black hole

Using a variant of superstring theory, a group of Japanese researchers derive an expression for the underlying thermodynamics of a black hole, all while testing the idea of a gauge-gravity duality.

A paper set to appear in an upcoming issue of Physical Review Letters uses one type of superstring theory to describe what the interior of a black hole would look like, thermodynamically speaking.
Using a stack of N D0-branes (D0 branes are really just membranes that are a single point), the authors attempt to probe the theory of gauge-gravity duality. In the process, they provide an idea of what a black hole looks like from the inside - assuming that their flavour of type IIA superstring theory describes reality. The gauge-gravity duality proposes that, in a given theory of reality, the force of gravity is decoupled from the gauge theory that describes other phenomena. If correct, this would imply that phenomena or quantities in either gravity or the gauge theory would have a direct analogue in the other. To date, this has not been proven for any model.

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Title: Higher derivative corrections to black hole thermodynamics from supersymmetric matrix quantum mechanics
Authors: Masanori Hanada, Yoshifumi Hyakutake, Jun Nishimura, Shingo Takeuchi
(Version v2)

We perform a direct test of the gauge-gravity duality associated with the system of N D0-branes in type IIA superstring theory at finite temperature. Based on the fact that higher derivative corrections to the type IIA supergravity action start at the order of \alpha', we derive the internal energy in expansion around infinite 't Hooft coupling up to the subleading term with one unknown coefficient. The power of the subleading term is shown to be nicely reproduced by the Monte Carlo data obtained nonperturbatively on the gauge theory side at finite but large effective (dimensionless) 't Hooft coupling constant. This suggests, in particular, that the open strings attached to the D0-branes provide the microscopic origin of the black hole thermodynamics of the dual geometry including \alpha' corrections. The coefficient of the subleading term extracted from the fit to the Monte Carlo data provides a prediction for the gravity side, which can be checked once the complete form of the O(\alpha') corrections to the supergravity action is obtained.

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Do hundreds of black holes dot the Milky Way?
Black holes are thought to be common in the universe, with a supermassive gobbler lurking at the core of galaxies such as our own Milky Way. But might they also be found roaming outside the galactic centers?

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