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Black Holes
ljk4-1
post Dec 12 2005, 03:58 PM
Post #16


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Paper: astro-ph/0512241

Date: Fri, 9 Dec 2005 06:09:19 GMT (23kb)

Title: Capture of a Red Giant by the Black Hole Sgr A* as a Possible Origin for
the TeV Gamma-Rays from the Galactic Center

Authors: Y. Lu, K.S. Cheng & Y.F. Huang

Comments: 15 pages, 1 figure, Accepted to ApJ
\\
Non-thermal TeV $\gamma$-ray emission within multi-pc scale has been observed
from the center region of our galaxy. We argue that these $\gamma$-rays are the
result of a transient activity of the massive black hole Sgr A$^*$ which
resides at the Galactic center. About thousands of years ago, the black hole
may have experienced an active phase by capturing a red giant star and forming
an accretion disk, temporarily behaving like an active galactic nuclear. A
powerful jet, which contains plenty of high speed protons, was launched during
the process. These runaway protons interact with the dense ambient medium,
producing TeV $\gamma$-ray emission through the $\pi^\circ$-decay process. We
show that the total energy deposited in this way is large enough to account for
observations. The diffusion length of protons is also consistent with the
observed size of the TeV source.

\\ ( http://arXiv.org/abs/astro-ph/0512241 , 23kb)


--------------------
"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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Guest_Richard Trigaux_*
post Dec 12 2005, 04:24 PM
Post #17





Guests






An intriguing thing about black hole evaporation is as follows.

As Hawking stated, a black hole may elit a black body-like thermal electromagnetic radiation, becomming hotter and hotter when the black hole becomes smaller.

But if so, what become the electric charge and the baryonic number* of the black hole? In order to decay, a black hole has to emit also protons and electrons. The same process Hawking described allows for emission of protons and electrons too, but what is said about this?

A black hole with a mass LESS than allowed by its baryonic number (its equivalent mass in hydrogen) need to receive energy to emit protons, and if it emits only protons, its electric charge will become so enormous that it will mandatorily call back any emitted particle.



*baryonic number is a fundamental constant of quantum physics, which is 1 for the proton and any other particle of the same family of 16 (neutron, hyperon, etc...) and -1 for the corresponding anti-particules. In any nuclear reaction, the baryonic number cannot change, and this sets the possible and impossible reactions. The baryonic number of a potato is the number of protons and neutrons it contains. In order to go to a fully rationalized metric system, grocers should price potatoes after their baryonic number rather than their mass. rolleyes.gif
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ljk4-1
post Dec 12 2005, 05:40 PM
Post #18


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Paper: astro-ph/0512211

Date: Thu, 8 Dec 2005 01:21:59 GMT (429kb)

Title: On The Nature of the Compact Dark Mass at the Galactic Center

Authors: Avery E. Broderick (1) and Ramesh Narayan (1,2) ((1) Institute for
Theory and Computation, (2) Harvard University)

Comments: 6 pages, 2 figures, submitted to ApJ Letters
\\
We consider a model in which Sgr A*, the 3.5x10^6 M_sun supermassive black
hole candidate at the Galactic Center, is a compact object with a surface.
Given the very low quiescent luminosity of Sgr A* in the near infrared, the
existence of a hard surface, even in the limit in which the radius approaches
the horizon, places severe constraints upon the steady mass accretion rate in
the source, requiring dM/dt < 10^-12 M_sun/yr. This limit is well below the
minimum accretion rate needed to power the observed submillimeter luminosity of
Sgr A*. We thus argue that Sgr A* does not have a surface, i.e., it must have
an event horizon. The argument could be made more restrictive by an order of
magnitude with microarcsecond resolution imaging, e.g., with submillimeter
VLBI.

\\ ( http://arXiv.org/abs/astro-ph/0512211 , 429kb)


--------------------
"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 Dec 16 2005, 05:44 AM
Post #19


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Paper: astro-ph/0512350

Date: Tue, 13 Dec 2005 23:58:06 GMT (110kb)

Title: Supermassive Black Holes at the Center of Galaxies

Authors: Christopher J. Greenwood

Comments: 11 pages, 3 figures
\\
This was my final paper for the AST 308 Galaxies class at Michigan State
University. Using many sources I was able to compile a moderate amount of
information concerning the evidence for, and the formation of Supermassive
Black Holes.

\\ ( http://arXiv.org/abs/astro-ph/0512350 , 110kb)


--------------------
"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 Dec 16 2005, 05:46 AM
Post #20


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Paper: astro-ph/0512358
Date: Wed, 14 Dec 2005 09:58:30 GMT (34kb)

Title: GRB 050911: a black hole - neutron star merger or a naked GRB

Authors: K.L. Page (1), A.R. King (1), A.J. Levan (2), P.T. O'Brien (1), J.P
Osborne (1), S.D. Barthelmy (5), A.P. Beardmore (1), D.N. Burrows (3), S.
Campana (4), N. Gehrels (5), J. Graham (6), M.R. Goad (1), O. Godet (1), Y.
Kaneko (7), J.A. Kennea (3), C.B. Markwardt (5), D.E. Reichart (8), T.
Sakamoto (5) & N.R. Tanvir (2) ((1) University of Leicester; (2) University
of Hertfordshire; (3) PSU; (4) Osservatorio di Brera, Merate; (5) GSFC;
(6)STScI; (7) NSSTC; (8) University of North Carolina)

Comments: 4 pages using emulateapj; 2 figures. Accepted for publication in ApJ
Letters
\\
GRB 050911, discovered by the Swift Burst Alert Telescope, was not seen 4.6
hr later by the Swift X-ray Telescope, making it one of the very few X-ray
non-detections of a Gamma-Ray Burst (GRB) afterglow at early times. The
gamma-ray light-curve shows at least three peaks, the first two of which (~T_0
- 0.8 and T_0 + 0.2 s, where T_0 is the trigger time) were short, each lasting
0.5 s. This was followed by later emission 10-20 s post-burst. The upper limit
on the unabsorbed X-ray flux was 1.7 x 10^-14 erg cm^-2 s^-1 (integrating 46 ks
of data taken between 11 and 18 September), indicating that the decay must have
been rapid. All but one of the long bursts detected by Swift were above this
limit at ~4.6 hr, whereas the afterglows of short bursts became undetectable
more rapidly. Deep observations with Gemini also revealed no optical afterglow
12 hr after the burst, down to r=24.0 (5-sigma limit). We speculate that GRB
050911 may have been formed through a compact object (black hole-neutron star)
merger, with the later outbursts due to a longer disc lifetime linked to a
large mass ratio between the merging objects. Alternatively, the burst may have
occured in a low density environment, leading to a weak, or non-existent,
forward shock - the so-called 'naked GRB' model.

\\ ( http://arXiv.org/abs/astro-ph/0512358 , 34kb)

Paper: astro-ph/0512344
Date: Tue, 13 Dec 2005 21:05:40 GMT (212kb)

Title: Hypervelocity intracluster stars ejected by supermassive black hole
binaries

Authors: Kelly Holley-Bockelmann, Steinn Sigurdsson, J. Christopher Mihos, John
J. Feldmeier, Robin Ciardullo, and Cameron McBride

Comments: 4 pages, 3 color figures. Submitted to ApJ Letters
\\
Hypervelocity stars have been recently discovered in the outskirts of
galaxies, such as the unbound star in the Milky Way halo, or the three
anomalously fast intracluster planetary nebulae (ICPNe) in the Virgo Cluster.
These may have been ejected by close 3-body interactions with a binary
supermassive black hole (SMBBH), where a star which passes within the semimajor
axis of the SMBBH can receive enough energy to eject it from the system. Stars
ejected by SMBBHs may form a significant sub-population with very different
kinematics and mean metallicity than the bulk of the intracluster stars. The
number, kinematics, and orientation of the ejected stars may constrain the mass
ratio, semimajor axis, and even the orbital plane of the SMBBH. We investigate
the evolution of the ejected debris from a SMBBH within a clumpy and
time-dependent cluster potential using a high resolution, self-consistent
cosmological N-body simulation of a galaxy cluster. We show that the predicted
number and kinematic signature of the fast Virgo ICPNe is consistent with
3-body scattering by a SMBBH with a mass ratio $10:1$ at the center of M87.

\\ ( http://arXiv.org/abs/astro-ph/0512344 , 212kb)


--------------------
"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 Dec 20 2005, 03:40 PM
Post #21


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Paper: astro-ph/0512455

Date: Sat, 17 Dec 2005 09:03:45 GMT (15kb)

Title: Feedback Limits Rapid Growth of Seed Black Holes at High Redshift

Authors: J.-M. Wang (1), Y.-M. Chen (1) and C. Hu (2,1) (1 IHEP, Beijing, 2
NAOC, Beijing)

Comments: 4 pages in emulateapj5.sty, 1 color figure. to appear in The
Astrophysical Journal Letters
\\
Seed black holes formed in the collapse of population III stars have been
invoked to explain the presence of supermassive black holes at high redshift.
It has been suggested that a seed black hole can grow up to $10^{5\sim 6}\sunm$
through highly super-Eddington accretion for a period of $\sim 10^{6\sim 7}$ yr
between redshift $z=20\sim 24$. We studied the feedback of radiation pressure,
Compton heating and outflow during the seed black hole growth. It is found that
its surrounding medium fueled to the seed hole is greatly heated by Compton
heating. For a super-critical accretion onto a $10^3\sunm$ seed hole, a Compton
sphere (with a temperature $\sim 10^6$K) forms in a timescale of $1.6\times
10^3$yr so that the hole is only supplied by a rate of $10^{-3}$ Eddington
limit from the Compton sphere. Beyond the Compton sphere, the kinetic feedback
of the strong outflow heats the medium at large distance, this leads to a
dramatical decrease of the outer Bondi accretion onto the black hole and avoid
the accumulation of the matter. The highly super-critical accretion will be
rapidly halted by the strong feedback. The seed black holes hardly grow up at
the very early universe unless the strong feedback can be avoided.

\\ ( http://arXiv.org/abs/astro-ph/0512455 , 15kb)


--------------------
"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 Dec 22 2005, 04:41 PM
Post #22


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Paper: astro-ph/0512515

Date: Wed, 21 Dec 2005 00:18:33 GMT (183kb)

Title: A size of ~1 AU for the radio source Sgr A* at the centre of the Milky
Way Galaxy

Authors: Zhi-Qiang Shen, K. Y. Lo, M.-C. Liang, Paul T. P. Ho, J.-H. Zhao

Comments: 18 pages, 4 figures

Journal-ref: Nature, 438(2005)62
\\
Although it is widely accepted that most galaxies have supermassive black
holes (SMBHs) at their centers^{1-3}, concrete proof has proved elusive.
Sagittarius A* (\sgras)^4, an extremely compact radio source at the center of
our Galaxy, is the best candidate for proof^{5-7}, because it is the closest.

Previous Very Long Baseline Interferometry (VLBI) observations (at 7mm) have
detected that \sgras is ~2 astronomical unit (AU) in size^8, but this is still
larger than the "shadow" (a remarkably dim inner region encircled by a bright
ring) arising from general relativistic effects near the event horizon^9.

Moreover, the measured size is wavelength dependent^{10}. Here we report a
radio image of \sgras at a wavelength of 3.5mm, demonstrating that its size is
$\sim$1 AU. When combined with the lower limit on its mass^{11}, the lower
limit on the mass density is 6.5x10^{21} Msun pc^{-3}, which provides the most
stringent evidence to date that \sgras is an SMBH. The power-law relationship
between wavelength and intrinsic size (size $\propto$ wavelength^{1.09}),
explicitly rules out explanations other than those emission models with
stratified structure, which predict a smaller emitting region observed at a
shorter radio wavelength.

\\ ( http://arXiv.org/abs/astro-ph/0512515 , 184kb)


--------------------
"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 Dec 23 2005, 05:08 PM
Post #23


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Paper (*cross-listing*): hep-th/0512268

Date: Wed, 21 Dec 2005 11:04:12 GMT (16kb)

Title: A fluid of black holes at the beginning of the Universe

Authors: P. Diaz, M.A. Per, A.Segui

Comments: Talk given at TAUP 2005, Zaragoza, Spain, 10-14 Sep 2005
\\
The most entropic fluid can be related to a dense gas of black holes that we
use to study the beginning of the universe. We encounter difficulties to
compatibilize an adiabatic expansion with the growing area for the coalescence
of black holes. This problem may be circumvented for a quantum black hole
fluid, whose classical counterpart can be described by a percolating process at
the critical point. This classical regime might be related to the energy
content of the current universe.

\\ ( http://arXiv.org/abs/hep-th/0512268 , 16kb)


--------------------
"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 Dec 26 2005, 06:40 PM
Post #24


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Group: Members
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Member No.: 430



Just in case anyone is wondering what a Black Holes topic is doing in the Voyager section:

http://www.patrawlings.com/images/large/S140.jpg


--------------------
"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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nprev
post Dec 27 2005, 02:18 AM
Post #25


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Member No.: 602



QUOTE (ljk4-1 @ Dec 26 2005, 11:40 AM)
Just in case anyone is wondering what a Black Holes topic is doing in the Voyager section:

http://www.patrawlings.com/images/large/S140.jpg
*


laugh.gif laugh.gif ...did the other Voyager acquire that image? Very clever.


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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ljk4-1
post Dec 30 2005, 05:27 PM
Post #26


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Paper: astro-ph/0512621

Date: Tue, 27 Dec 2005 18:24:40 GMT (91kb)

Title: Astrometric Monitoring of Stellar Orbits at the Galactic Center with a
Next Generation Large Telescope

Authors: Nevin N. Weinberg (1, 2), Milos Milosavljevic (1), Andrea M. Ghez (3)
((1) Caltech, (2) KITP, (3) UCLA)

Comments: 8 pages, 3 figures. ASP Conf. Series "Astrometry in the Age of the
Next Generation of Large Telescopes", 2005, v.338, eds. P. Kenneth Seidelmann
and Alice K. B. Monet

Journal-ref: ASP Conf. Proc. 338 (2005) 252
\\
We show that with a Next Generation Large Telescope one can detect the
accelerated motions of ~100 stars orbiting the massive black hole at the
Galactic center. The positions and velocities of these stars will be measured
to astrometric and spectroscopic precision several times better than currently
attainable enabling detailed measurements of the gravitational potential in the
neighborhood of the massive black hole. We show that the monitoring of stellar
motions with such a telescopes enables: (1) a measurement of the Galactic
center distance R_0 to better than 0.1% accuracy, (2) a measurement of the
extended matter distribution near the black hole, including that of the exotic
dark matter, (3) a detection of general relativistic effects due to the black
hole including the prograde precession of stars and possibly the black hole
spin, and (4) a detection of gravitational encounters between monitored stars
and stellar remnants that accumulate near the Galactic center. Such encounters
probe the mass function of the remnants.

\\ ( http://arXiv.org/abs/astro-ph/0512621 , 91kb)


--------------------
"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 Dec 30 2005, 05:33 PM
Post #27


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Paper: astro-ph/0512625

Date: Wed, 28 Dec 2005 10:22:34 GMT (861kb)

Title: Flares of Sagittarius a* at Millimeter Wavelengths

Authors: Atsushi Miyazaki, Takahiro Tsutsumi, Makoto Miyoshi, Masato Tsuboi,
Zhi-Qiang Shen

Comments: 4 pages. Presented at the XXVIIIth Geleral Assembly of the URSI, Oct
2005, India
\\
We have performed monitoring observations of the flux density toward the
Galactic center compact radio source, Sagittarius A* (Sgr A*), which is a
supermassive black hole, from 1996 to 2005 using the Nobeyama Millimeter Array
of the Nobeyama Radio Observatory, Japan. These monitoring observations of Sgr
A* were carried out in the 3- and 2-mm (100 and 140 GHz) bands, and we have
detected several flares of Sgr A*. We found intraday variation of Sgr A* in the
2000 March flare. The twofold increase timescale is estimated to be about 1.5
hr at 140 GHz. This intraday variability suggests that the physical size of the
flare-emitting region is compact on a scale at or below about 12 AU (~150 Rs;
Schwarzschild radius). On the other hand, clear evidence of long-term periodic
variability was not found from a periodicity analysis of our current millimeter
data set.

\\ ( http://arXiv.org/abs/astro-ph/0512625 , 861kb)


--------------------
"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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Guest_Richard Trigaux_*
post Dec 30 2005, 05:45 PM
Post #28





Guests






QUOTE (ljk4-1 @ Dec 30 2005, 05:33 PM)
This intraday variability suggests that the physical size of the
flare-emitting region is compact on a scale at or below about 12 AU (~150 Rs;
Schwarzschild radius).


That makes about 20 million kilometres in diametre for the black hole (the Schwarzchild sphere). The size of a giant star.

Expectably such a thing is able to swallow a Sun-sized star without letting any matter escape, only large stars could let some matter out. But even in the case of a small star like the Sun, it would be elongated by the tides, and become much more luminous and voluminous just before disappearing. Perhaps even in this case there could be some ejection of matter. Not accounting with the case where even a minor star comes just grazing the surface of the Schwarzchild sphere; in this case there could be strong ejections of hot matter, coming after to form an accretion disk and a long time of increased activity.

But the minor activity observed is likely only the activity of a smaller accretion disk gathering clouds of gas and dust.
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ljk4-1
post Jan 4 2006, 03:07 AM
Post #29


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Paper: astro-ph/0512657

Date: Fri, 30 Dec 2005 20:55:34 GMT (102kb)

Title: EXIST: All-Sky Hard X-ray Imaging and Spectral-Temporal Survey for Black
Holes

Authors: Jonathan E. Grindlay (and the EXIST Team)

Comments: 4 pages, 1 figure. Presented at LBL Surveys Workshop

Journal-ref: New Astronomy Reviews, Volume 49, iss. 7-9, pp. 436-439 (2005)
\\
The Energetic X-ray Imaging Survey Telescope (EXIST) is under study for the
proposed Black Hole Finder Probe, one of the three Einstein Probe missions in
NASA's proposed Beyond Einstein Program. EXIST would have unique capabilities:
it would survey the full sky at 5-600 keV each 95min orbit with 0.9-5 arcmin,
10microsec - 45min, and ~0.5-5 keV resolution to locate sources to 10arcsec and
enable black holes to be surveyed and studied on all scales. With 5sigma survey
sensitivity (0.5-1y) Fx(40-80 keV) ~5 x 10^-13 cgs, or comparable to the ROSAT
soft X-ray (0.3-2.5 keV) sky survey, a large sample (~2-4 x 10^4) of obscured
AGN will be identified and a complete sample of accreting stellar mass BHs in
the Galaxy will be found. The all-sky/all-time coverage will allow rare events
to be measured, such as possible stellar disruption flares from dormant AGN out
to ~200 Mpc. A large sample (~2-3/day) of GRBs will be located (<~10arcsec) at
sensitivities and bandwidths much greater than previously and likely yield the
highest redshift events and constraints on Pop III BHs. An outline of the
mission design from the ongoing concept study is presented.

\\ ( http://arXiv.org/abs/astro-ph/0512657 , 102kb)


Paper: astro-ph/0512642

Date: Thu, 29 Dec 2005 20:32:57 GMT (239kb)

Title: Massive Black Hole Binaries from Collisional Runaways

Authors: M. Atakan G\"urkan, John M. Fregeau and Frederic A. Rasio
(Northwestern University)

Comments: 4 pages with emulateapj. Submitted to ApJ Letters
\\
Recent theoretical work has solidified the viability of the collisional
runaway scenario in young dense star clusters for the formation of very massive
stars (VMSs), which may be precursors to intermediate-mass black holes (IMBHs).
We present first results from a numerical study of the collisional runaway
process in dense star clusters containing primordial binaries. Stellar
collisions during binary scattering encounters offer an alternate channel for
runaway growth, somewhat independent of direct collisions between single stars.
We find that clusters with binary fractions >~10% yield two VMSs via
collisional runaways, presenting the exotic possibility of forming IMBH--IMBH
binaries in star clusters. We discuss the implications for gravitational wave
observations, and the impact on cluster structure.

\\ ( http://arXiv.org/abs/astro-ph/0512642 , 239kb)

------------------------------------------------------------------------------
\\
Paper: astro-ph/0512643

Date: Thu, 29 Dec 2005 21:40:40 GMT (223kb)

Title: G359.95-0.04: Pulsar Candidate Near Sgr A*

Authors: Q. D. Wang (UMass/IAS), F. J. Lu (UMass/IHEP), and E. V. Gotthelf
(Columbia U.)

Comments: 11 pages, accepted for publication in MNRAS, higher resolution
version at http://www.astro.umass.edu/~wqd/papers/xcomet.pdf
\\
We report the discovery of a prominent nonthermal X-ray feature located near
the Galactic center that we identify as an energetic pulsar wind nebula. This
feature, G359.95-0.04, lies 1 lyr north of Sgr A* (in projection), is
comet-like in shape, and has a power law spectrum that steepens with increasing
distance from the putative pulsar. The distinct spectral and spatial X-ray
characteristics of the feature are similar to those belonging the rare class of
ram-pressure confined pulsar wind nebulae. The luminosity of the nebula at the
distance of \sgra, consistent with the inferred X-ray absorptions, is 1 10^{34}
ergs s^{-1} in the 2--10 keV energy band. The cometary tail extends back to a
region centered at the massive stellar complex IRS 13 and surrounded by
enhanced diffuse X-ray emission, which may represent an associated supernova
remnant. Furthermore, the inverse Compton scattering of the strong ambient
radiation by the nebula consistently explains the observed TeV emission from
the Galactic center. We also briefly discuss plausible connections of
G359.95-0.04 to other high-energy sources in the region, such as the young
stellar complex IRS 13 and SNR Sgr A East.

\\ ( http://arXiv.org/abs/astro-ph/0512643 , 223kb)


--------------------
"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 Jan 5 2006, 06:31 PM
Post #30


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A DYING STAR REVEALS MORE EVIDENCE FOR A NEW KIND OF BLACK HOLE

Scientists using NASA's Rossi X-ray Timing Explorer have found a doomed star orbiting what appears to be a medium-sized black hole a theorized "in-between" category of black hole that has eluded confirmation and frustrated scientists for more than a decade.

With the discovery of the star and its orbital period, scientists are now one step away from measuring the mass of such a black hole, a step which would help verify its existence. The star's period and location already fit into the main theory of how these black holes could form.

A team led by Prof. Philip Kaaret of the University of Iowa, Iowa City, announced these results today in Science Express. The results will also appear in the Jan. 27 issue of Science.

"We caught this otherwise ordinary star in a unique stage in its evolution, toward the end of its life when it has bloated into a red giant phase," said Kaaret. "As a result, gas from the star is spilling into the black hole, causing the whole region to light up. This is a well-studied region of the sky, and we spotted the star with a little luck and a lot of perseverance."

http://www.nasa.gov/centers/goddard/news/t..._blackhole.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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