* Astronomy

Blobrana · L

RE: Black Holes

Blobrana · L

Astronomers think that many - perhaps all - galaxies in the universe contain massive black holes at their centres. New observations with the Submillimeter Array now suggest that such colossal black holes were common even 12 billion years ago, when the universe was only 1.7 billion years old and galaxies were just beginning to form. The new conclusion comes from the discovery of two distant galaxies, both with black holes at their heart, which are involved in a spectacular collision. 4C60.07, the first of the galaxies to be discovered, came to astronomers' attention because of its bright radio emission. This radio signal is one telltale sign of a quasar - a rapidly spinning black hole that is feeding on its home galaxy.

Read more

Blobrana · L

Title: The High-Mass End of the Black Hole Mass Function: Mass Estimates in Brightest Cluster Galaxies
Authors: E. Dalla Bonta' (1,2), L. Ferrarese (2), E. M. Corsini (1), J. Miralda-Escude' (3), L. Coccato (4), M. Sarzi (5), A. Pizzella (1), A. Beifiori (1) ((1) Dipartimento di Astronomia, Universita' degli Studi di Padova, Italy, (2) Herzberg Institute of Astrophysics, Victoria, CA, (3) Institut de Ciencies de l'Espai, IEEC-CSIC/ICREA, (4) Max-Planck-Institut fuer extraterrestrische Physik, Garching bei Muenchen, Germany, (5) Centre for Astrophysics Research, University of Hertfordshire, Hatfield, UK)

We present Hubble Space Telescope imaging and spectroscopic observations of three Brightest Cluster Galaxies, Abell 1836-BCG, Abell 2052-BCG, and Abell 3565-BCG, obtained with the Wide Field and Planetary Camera 2, the Advanced Camera for Surveys and the Space Telescope Imaging Spectrograph. The data provide detailed information on the structure and mass profile of the stellar component, the dust optical depth, and the spatial distribution and kinematics of the ionised gas within the innermost region of each galaxy. Dynamical models, which account for the observed stellar mass profile and include the contribution of a central supermassive black hole (SBH), are constructed to reproduce the kinematics derived from the Halpha and [N II](lambda 6548,6583) emission lines. Secure SBH detection with M_bh=3.61(+0.41,-0.50)x10^9 M_sun and M_bh=1.34(+0.21,-0.19)x10^9 M_sun, respectively, are obtained for Abell 1836-BCG and Abell 3565-BCG, which show regular rotation curves and strong central velocity gradients. In the case of Abell 2052-BCG, the lack of an orderly rotational motion prevents a secure determination, although an upper limit of M_bh < 4.60x10^9 M_sun can be placed on the mass of the central SBH. These measurements represent an important step forward in the characterization of the high-mass end of the SBH mass function.

Read more (1363kb, PDF)

Blobrana · L

Computer simulation of a molecular cloud falling into a black hole (Science/AAAS)

The researchers modelled how molecular clouds are sucked into black holes

Astronomers have shed light on how stars can form around a massive black hole, defying conventional wisdom.
Scientists have long puzzled over how stars develop in so extreme conditions.
Molecular clouds - the normal birth places of stars - would be ripped apart by the immense gravity, a team explains in Science magazine.
But the researchers say that stars can form from elliptical discs - the relics of giant gas clouds torn apart by encounters with black holes.

Read more

Blobrana · L

For black holes, there appears to be very little room for mediocrity, astronomers have found.
A study suggests they come in either small or large sizes, but medium-sized ones are very rare or non-existent.
A team of astronomers has examined one of the best hiding places for a middleweight black hole, and found that it cannot possibly host one.

Read more

Blobrana · L

Black holes are sometimes huge cosmic beasts, billions of times the mass of our sun, and sometimes petite with just a few times the sun's mass. But do black holes also come in size medium? Research combining data from the European Space Agency's XMM-Newton space telescope and the W. M. Keck Observatory suggests that, for the most part, the answer is no.
Astronomers have long suspected that the most likely place to find a medium-mass black hole would be at the core of a miniature galaxy-like object called a globular cluster. Yet, nobody has been able to find one conclusively.
Now, a team of astronomers has thoroughly examined a globular cluster called RZ2109 and determined that it cannot possess a medium black hole. The findings suggest that the elusive objects do not lurk in globular clusters, and perhaps are very rare.

Read more

Blobrana · L

Title: Masses of Black Holes in the Universe
Authors: Janusz Ziolkowski (Copernicus Astronomical Center, Warsaw, Poland)

The different methods of determination of black holes (BHs) masses are presented for three classes of BHs observed in the Universe: stellar mass BHs, intermediate mass BHs (IMBHs) and supermassive BHs (SBHs). The results of these determinations are briefly reviewed: stellar mass BHs are found in the range of about 3 to about 20 solar masses, IMBHs in the range of a few hundreds to a few tens of thousands solar masses (the determinations are much less precise for these objects) and SBHs in the range of about 3x10^5 to about 6x10^10 solar masses.

Read more (30kb, PDF)

Blobrana · L

Title: The fuzzball proposal for black holes
Authors: Kostas Skenderis, Marika Taylor
(Version v2)

The fuzzball proposal states that associated with a black hole of entropy S there are exp S horizon-free non-singular solutions that asymptotically look like the black hole but generically differ from the black hole up to the horizon scale. These solutions, the fuzzballs, are considered to be the black hole microstates while the original black hole represents the average description of the system. The purpose of this report is to review current evidence for the fuzzball proposal, emphasizing the use of AdS/CFT methods in developing and testing the proposal. In particular, we discuss the status of the proposal for 2 and 3 charge black holes in the D1-D5 system, presenting new derivations and streamlining the discussion of their properties. Results to date support the fuzzball proposal but further progress is likely to require going beyond the supergravity approximation and sharpening the definition of a "stringy fuzzball". We outline how the fuzzball proposal could resolve longstanding issues in black hole physics, such as Hawking radiation and information loss. Our emphasis throughout is on connecting different developments and identifying open problems and directions for future research.

Read more (88kb, PDF)

Blobrana · L

Title: Discovery of a Relationship between Spiral Arm Morphology and Supermassive Black Hole Mass in Disk Galaxies
Authors: Seigar, Marc S.; Kennefick, Daniel; Kennefick, Julia; Lacy, Claud H. S.

We present a relationship between spiral arm pitch angle (a measure of the tightness of spiral structure) and the mass of supermassive black holes (BHs) in the nuclei of disk galaxies. We argue that this relationship is expected through a combination of other relationships, whose existence has already been demonstrated. The recent discovery of AGN in bulgeless disk galaxies suggests that halo concentration or virial mass may be one of the determining factors in BH mass. Taken together with the result that mass concentration seems to determine spiral arm pitch angle, one would expect a relation to exist between spiral arm pitch angle and supermassive BH mass in disk galaxies, and we find that this is indeed the case. We conclude that this relationship may be important for estimating evolution in BH masses in disk galaxies out to intermediate redshifts, since regular spiral arm structure can be seen in galaxies out to z~=1.

Read more

How does one weigh a supermassive black hole that is anywhere between a million and a billion times the mass of the Sun? The answer could be as easy as taking a snapshot of its surrounding galaxy.
A team of astronomers has concluded that the larger the black hole at the centre of a spiral galaxy, the tighter the galaxy's arms wrap around itself. If correct, the simple relationship would give researchers an easy way to learn about black holes up to 8 billion light years away thousands of times farther than most black hole masses can be resolved today.

Read more

Blobrana · L

While we may never know what it looks like inside a black hole, astronomers recently obtained one of the closest views yet.
The sighting allowed scientists to confirm theories about how these giant cosmic sinkholes spew out jets of particles travelling at nearly the speed of light.

Read more