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Black Holes
ljk4-1
post Feb 16 2006, 03:49 PM
Post #46


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Astrophysics, abstract
astro-ph/0602307

From: Rob Fender [view email]

Date: Tue, 14 Feb 2006 12:08:04 GMT (61kb)

A transient relativistic radio jet from Cygnus X-1

Authors: R.P. Fender (Southampton), A.M.Stirling (Manchester), R.E. Spencer (Manchester), I. Brown (Manchester), G.G. Pooley (MRAO), T.W.B. Muxlow (Manchester), J.C.A. Miller-Jones (Amsterdam)

Comments: Accepted for publication in MNRAS

We report the first observation of a transient relativistic jet from the canonical black hole candidate, Cygnus X-1, obtained with the Multi-Element Radio-Linked Interferometer Network (MERLIN). The jet was observed in only one of six epochs of MERLIN imaging of the source during a phase of repeated X-ray spectral transitions in 2004 Jan--Feb, and this epoch corresponded to the softest 1.5-12 keV X-ray spectrum. With only a single epoch revealing the jet, we cannot formally constrain its velocity. Nevertheless, several lines of reasoning suggest that the jet was probably launched 0.5-4.0 days before this brightening, corresponding to projected velocities of 0.2c < v_app < 1.6c, and an intrinsic velocity of > 0.3c. We also report the occurrence of a major radio flare from Cyg X-1, reaching a flux density of ~120 mJy at 15 GHz, and yet not associated with any resolvable radio emission, despite a concerted effort with MERLIN. We discuss the resolved jet in terms of the recently proposed 'unified model' for the disc-jet coupling in black hole X-ray binaries, and tentatively identify the 'jet line' for Cyg X-1. The source is consistent with the model in the sense that a steady jet appears to persist initially when the X-ray spectrum starts softening, and that once the spectral softening is complete the core radio emission is suppressed and transient ejecta / shock observed. However, there are some anomalies, and Cyg X-1 clearly does not behave like a normal black hole transient in progressing to the canonical soft / thermal state once the ejection event has happened.

http://arxiv.org/abs/astro-ph/0602307


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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ljk4-1
post Feb 17 2006, 09:07 PM
Post #47


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Astrophysics, abstract
astro-ph/0602363

From: Mitchell C. Begelman [view email]

Date: Thu, 16 Feb 2006 12:23:24 GMT (31kb)

Formation of Supermassive Black Holes by Direct Collapse in Pregalactic Halos

Authors: Mitchell C. Begelman, Marta Volonteri, Martin J. Rees

Comments: 10 pages, 2 figures, submitted to Monthly Notices of the Royal Astronomical Society

We describe a mechanism by which supermassive black holes can form directly in the nuclei of protogalaxies, without the need for seed black holes left over from early star formation. Self-gravitating gas in dark matter halos can lose angular momentum rapidly via runaway, global dynamical instabilities, the so-called "bars within bars" mechanism. This leads to the rapid buildup of a dense, self-gravitating core supported by gas pressure - surrounded by a radiation pressure-dominated envelope - which gradually contracts and is compressed further by subsequent infall. These conditions lead to such high temperatures in the central region that the gas cools catastrophically by thermal neutrino emission, leading to the formation and rapid growth of a central black hole.

We estimate the initial mass and growth rate of the black hole for typical conditions in metal-free halos with T_vir ~ 10^4 K, which are the first to be susceptible to runaway infall. The initial black hole should have a mass of <~ 20 solar masses, but in principle could grow at a super-Eddington rate until it reaches ~ 10^4-10^6 solar masses. Rapid growth may be limited by feedback from the accretion process and/or disruption of the mass supply by star formation or halo mergers. Even if super-Eddington growth stops at ~10^3-10^4 solar masses, this process would give black holes ample time to attain quasar-size masses by a redshift of 6, and could also provide the seeds for all supermassive black holes seen in the present universe.

http://arxiv.org/abs/astro-ph/0602363


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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ljk4-1
post Feb 22 2006, 07:30 PM
Post #48


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Group: Members
Posts: 2454
Joined: 8-July 05
From: NGC 5907
Member No.: 430



DEEP X-RAY SURVEYS REVEAL BLACK HOLE POPULATION
-----------------------------------------------

Data from X-ray observatory surveys show that black holes are much more
numerous and evolved differently than researchers would have expected,
according to a Penn State astronomer.

http://spaceflightnow.com/news/n0602/21blackholes/


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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ljk4-1
post Mar 29 2006, 04:28 PM
Post #49


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****

Group: Members
Posts: 2454
Joined: 8-July 05
From: NGC 5907
Member No.: 430



Astrophysics, abstract
astro-ph/0603761

From: Pedro Gonzalez-Diaz [view email]

Date: Tue, 28 Mar 2006 11:41:12 GMT (9kb)

Will black holes eventually engulf the universe?

Authors: Prado Martin-Moruno, Jose A. Jimenez Madrid, Pedro F. Gonzalez-Diaz

Comments: 4 pages, RevTex

Report-no: IMAFF-RCA-06-04

The Babichev-Dokuchaev-Eroshenko model for the accretion of dark energy onto black holes has been extended to deal with black holes with non-static metrics. The possibility that for an asymptotic observer a black hole with large mass will rapidly increase and eventually engulf the Universe at a finite time in the future has been studied by using reasonable values for astronomical parameters. It is concluded that such a phenomenon is forbidden for all black holes in quintessential cosmological models.

http://arxiv.org/abs/astro-ph/0603761


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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ljk4-1
post Jun 5 2006, 03:30 PM
Post #50


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Group: Members
Posts: 2454
Joined: 8-July 05
From: NGC 5907
Member No.: 430



Spacecraft may be able to determine if braneworld black holes exist right
in our Sol system.


Scientists Predict How to Detect a Fourth Dimension of Space

New theory of gravity challenges Einstein's general relativity

Thursday, May 25, 2006

Scientists at Duke and Rutgers universities have developed a mathematical framework they say will enable astronomers to test a new five-dimensional theory of gravity that competes with Einstein's General Theory of Relativity.

Charles R. Keeton of Rutgers and Arlie O. Petters of Duke base their work on a recent theory called the type II Randall-Sundrum braneworld gravity model. The theory holds that the visible universe is a membrane (hence "braneworld") embedded within a larger universe, much like a strand of filmy seaweed floating in the ocean. The "braneworld universe" has five dimensions -- four spatial dimensions plus time -- compared with the four dimensions -- three spatial, plus time -- laid out in the General Theory of Relativity.

...

When we estimated how far braneworld black holes might be from Earth, we were surprised to find that the nearest ones would lie well inside Pluto's orbit," Keeton said.

Petters added, "If braneworld black holes form even 1 percent of the dark matter in our part of the galaxy -- a cautious assumption -- there should be several thousand braneworld black holes in our solar system."

Full article here:

http://dukenews.duke.edu/2006/05/braneworld.html


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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+Quote Post

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