* Astronomy

Could a 'naked' singularity, the bare core of a black hole, be sitting at the centre of our galaxy? A new study shows how astronomers could detect such a brazen object which is so dense it would shred the known laws of physics.
Singularities exist in the heart of every black hole, according to Einstein's general theory of relativity. When matter collapses under its own gravity, it forms either a point or a ring-shaped line of infinite density. But each of these singularities is cloaked by a so-called event horizon where light and everything else is inexorably sucked inwards. So we could never see one.
Unless, that is, there are black holes that spin at extreme speeds. A spinning black hole drags nearby space around with it, and if it spins fast enough, then light and matter could escape from right by the singularity, because they would be flung outwards by the dizzying rotation.

This gravitational tornado would have no event horizon, and the singularity would be exposed.

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An Indian origin led team of astronomers, has for the first time, spotted a black hole belching out a burst of gamma rays after gulping down part of a nearby star.

"This kind of event is probably much more common than the ones normally observed by Swift. The reason, we haven't seen something like this before, is not because it's rare, but because it's a low-energy event. The burst is intrinsically about 100 trillion times less powerful than previously observed long GRBs. If the same thing happened in another galaxy, we just don't have detectors that are sensitive enough to see it" - Mansi Kasliwal of Caltech in Pasadena, US.

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Supermassive black holes have been discovered to grow more rapidly in young galaxy clusters, according to new results from NASA's Chandra X-ray Observatory. These "fast-track" supermassive black holes can have a big influence on the galaxies and clusters that they live in.
Using Chandra, scientists surveyed a sample of clusters and counted the fraction of galaxies with rapidly growing supermassive black holes, known as active galactic nuclei (or AGN). The data show, for the first time, that younger, more distant galaxy clusters contained far more AGN than older, nearby ones.
Galaxy clusters are some of the largest structures in the Universe, consisting of many individual galaxies, a few of which contain AGN. Earlier in the history of the universe, these galaxies contained a lot more gas for star formation and black hole growth than galaxies in clusters do today. This fuel allows the young cluster black holes to grow much more rapidly than their counterparts in nearby clusters.

Credit: NASA/CXC/Ohio State Univ./J.Eastman et al
JPEG (150 kb)	Tiff (5 MB)	PS (2.8 MB)

Position(J2000):      RA 05h 42m 50.20s | Dec -41° 00º 6.98"

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Title: "Black Star" or Astrophysical Black Hole?
Authors: K. Petrovay

Recently wide publicity has been given to a claim by T. Vachaspati that "black holes do not exist", that the objects known as black holes in astrophysics should rather be called "black stars" and they not only do not have event horizons but actually can be the source of spectacular gamma ray bursts. In this short essay (no flimsier than the original preprint where these extravagant claims appeared) I demonstrate that these ill-considered claims are clearly wrong. Yet they present a good occasion to reflect on some well known but little discussed conceptual difficulties which arise when applying relativistic terminology in an astrophysical context.

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