Title: Accelerating black hole in 2+1 dimensions and 3+1 black (st)ring Authors: Marco Astorino (Version v2)

A C-metric type solution for general relativity with cosmological constant is presented in 2+1 dimensions. It is interpreted as a three-dimensional black hole accelerated by a strut. Positive values of the cosmological constant are admissible too. Some embeddings of this metric in the 3+1 space-time are considered: accelerating BTZ black string and a black ring where the gravitational force is sustained by the acceleration.

Answers to black hole evolution beyond the horizon?

One of the most important predictions of Einstein's theory of General Relativity is the existence of black holes. The dynamics of these systems are not yet fully understood, but researchers from Queen Mary, University of London have now provided a rigorous way of determining the evolutionary stage of a black hole by analysing the region outside where matter cannot escape, the event horizon. Dr Thomas Bäckdahl and Dr Juan A. Valiente Kroon at Queen Mary's School of Mathematical Sciences have developed a method based on properties of the Kerr solution, a time-independent solution to the equations of General Relativity. The Kerr solution is one of the few exact solutions to the equations of General Relativity, and describes a rotating, stationary (time-independent) black hole. It is also proposed that it describes the final evolutionary stage of any dynamical (time-dependent) black hole. Read more

Title: The "non-Kerrness" of domains of outer communication of black holes and exteriors of stars Authors: T. Bäckdahl, J. A. Valiente Kroon

In this article we construct a geometric invariant for initial data sets for the vacuum Einstein field equations (\mathcal{S},h_{ab},K_{ab}), such that \mathcal{S} is a 3-dimensional manifold with an asymptotically Euclidean end and an inner boundary \partial \mathcal{S} with the topology of the 2-sphere. The hypersurface \mathcal{S} can be though of being in the domain of outer communication of a black hole or in the exterior of a star. The geometric invariant vanishes if and only if (\mathcal{S},h_{ab},K_{ab}) is an initial data set for the Kerr spacetime. The construction makes use of the notion of Killing spinors and of an expression for a \emph{Killing spinor candidate} which can be constructed out of concomitants of the Weyl tensor.

Astronomers Discover Close-knit Pairs of Massive Black Holes

Astronomers at the California Institute of Technology (Caltech), University of Illinois at Urbana-Champaign (UIUC), and University of Hawaii (UH) have discovered 16 close-knit pairs of supermassive black holes in merging galaxies.

The discovery, based on observations done at the W. M. Keck Observatory on Hawaii's Mauna Kea, is being presented in Seattle on January 12 at the meeting of the American Astronomical Society, and has been submitted for publication in the Astrophysical Journal.

Title: Measuring the Spins of Accreting Black Holes Authors: Jeffrey E. McClintock, Ramesh Narayan, Shane W. Davis, Lijun Gou, Akshay Kulkarni, Jerome A. Orosz, Robert F. Penna, Ronald A. Remillard, James F. Steiner

A typical galaxy is thought to contain tens of millions of stellar-mass black holes, the collapsed remnants of once massive stars, and a single nuclear supermassive black hole. Both classes of black holes accrete gas from their environments. The accreting gas forms a flattened orbiting structure known as an accretion disk. During the past several years, it has become possible to obtain measurements of the spins of the two classes of black holes by modelling the X-ray emission from their accretion disks. Two methods are employed, both of which depend upon identifying the inner radius of the accretion disk with the innermost stable circular orbit (ISCO), whose radius depends only on the mass and spin of the black hole. In the Fe K method, which applies to both classes of black holes, one models the profile of the relativistically-broadened iron line with a special focus on the gravitationally redshifted red wing of the line. In the continuum-fitting method, which has so far only been applied to stellar-mass black holes, one models the thermal X-ray continuum spectrum of the accretion disk. We discuss both methods, with a strong emphasis on the continuum-fitting method and its application to stellar-mass black holes. Spin results for eight stellar-mass black holes are summarized. These data are used to argue that the high spins of at least some of these black holes are natal, and that the presence or absence of relativistic jets in accreting black holes is not entirely determined by the spin of the black hole.

TAU astronomers identify the epoch of the first fast growth of black holes

Most galaxies in the universe, including our own Milky Way, harbour super-massive black holes varying in mass from about one million to about 10 billion times the size of our sun. To find them, astronomers look for the enormous amount of radiation emitted by gas which falls into such objects during the times that the black holes are "active," i.e., accreting matter. This gas "infall" into massive black holes is believed to be the means by which black holes grow. Now a team of astronomers from Tel Aviv University, including Prof. Hagai Hetzer and his research student Benny Trakhtenbrot, have determined that the era of first fast growth of the most massive black holes occurred when the universe was only about 1.2 billion years old - not two to four billion years old, as was previously believed - and they're growing at a very fast rate. Read more

Title: Black-Hole Mass and Growth Rate at z~4.8: A Short Episode of Fast Growth Followed by Short Duty Cycle Activity Authors: Benny Trakhtenbrot, Hagai Netzer, Paulina Lira, Ohad Shemmer (Version v2)

We present new Gemini-North/NIRI and VLT/SINFONI H-band spectroscopy for a flux limited sample of 40 z~4.8 active galactic nuclei, selected from the Sloan Digital Sky Survey. The sample probably contains the most massive active black holes (BHs) at this redshift and spans a broad range in bolometric luminosity, 2.7x10^46< L_bol < 2.4x10^47 erg/sec. The high-quality observations and the accurate fitting of the MgII(2800A) line, enable us to study, systematically, the distribution of BH mass (M_BH) and normalized accretion rate (L/L_Edd) at z~4.8. We find that 10^8 < M_BH < 6.6x10^9 M_sun, with a median of ~8.4x10^8 M_sun. We also find that 0.2 < L/L_Edd < 3.9 with a median of ~0.6. Most of these sources had enough time to grow to their observed mass at z~4.8 from z=20, assuming a range of seed BH masses, with ~40% that are small enough to be stellar remnants. Compared to previously studied samples at z~2.4 and 3.3, the masses of the z~4.8 BHs are typically lower by ~0.5 dex. and their L/L_Edd is higher by a similar factor. The new z~4.8 sample can be considered as the progenitor population of the most massive BHs at z~2.4 and 3.3. Such an evolutionary interpretation requires that the growth of the BHs from z~4.8 to z~3.3 and z~2.4 proceeds with short duty cycles, of about 10-20%, depending on the particular growth scenario.

US astronomers are confident an object studied for 30 years in the M100 galaxy is a black hole. If so, this would make it the nearest and youngest such object to Earth. Read more

Yale professors Charles Bailyn and Meg Urry talk about the mysterious world of black holes. Predicted by Einstein's theories, their existence was only confirmed observationally in the early 1980s. Professors Bailyn and Urry begin with a description of the two types of black hole -- stellar and supermassive -- and explain how astronomers look for and investigate objects that by their nature emit no observable radiation of any kind. This investigation uses both ground-based telescopes, such as the SMARTS telescope system in Chile, as well as space-based telescopes such as NASA's Fermi Gamma Ray telescope. The discussion then turns to current research at Yale that furthers our understanding of these powerful objects, how they affect the stars and galaxies around them, and what they tell us about the nature of the Universe.

Black hole mystery solved by magnetic star discovery

The discovery of a rare magnetic star - or magnetar - is challenging theories about the origin of black holes. Magnetars are a special type of neutron star with a powerful magnetic field. They are formed by gravitational collapse after the original, or progenitor star, dies and forms a catastrophic supernova. The new magnetar was found in an extraordinary star cluster known as Westerlund 1, located 16,000 light years away in the southern constellation of Ara (the Altar). Read more