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Black Holes
maryalien
post Dec 7 2005, 04:04 PM
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any one wanna talk black holes. i'm not a professional or anything. i vaguely remember hearing s. hawkin revising his opinion on it saying it wasnt a "worm hole" anymore and that it just destroys all matter and worth nothing else.

i only make my observations, childlike actually, to that of what happens on earth, and why shouldnt it happen in the rest of the universe. why should anything here (goverening law of physics, etc.) be different anywhere else?

just like a tornado, or water running down a drain (or that infamous lake that was drained by accident by some guys drilling and all the water drained into the salt mine, i cant remember the name now but a 6 inch hole sucked in a tanker), why wouldnt a black hole be that "event" that punched a hole into another "dimension/galaxy whatever" with less pressure.

and maybe all that "dark matter" is the "reminant" of what comes out of a black hole.

i dont know, just talking. my head is always "out there, out of earth..."

maryalien
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Guest_Richard Trigaux_*
post Dec 12 2005, 04:24 PM
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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
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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
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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
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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
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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
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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
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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
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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 #10


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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
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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
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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 #13





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
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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 #15


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From: NGC 5907
Member No.: 430



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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ljk4-1
post Jan 9 2006, 04:03 PM
Post #16


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Group: Members
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From: NGC 5907
Member No.: 430



Paper (*cross-listing*): gr-qc/0512160

Date: Thu, 29 Dec 2005 02:27:13 GMT (436kb)

Title: On gravitational-wave spectroscopy of massive black holes with the space
interferometer LISA

Authors: Emanuele Berti, Vitor Cardoso, Clifford M. Will

Comments: 44 pages, 21 figures, 10 tables
\\
Newly formed black holes are expected to emit characteristic radiation in the
form of quasi-normal modes, called ringdown waves, with discrete frequencies.
LISA should be able to detect the ringdown waves emitted by oscillating
supermassive black holes throughout the observable Universe. We develop a
multi-mode formalism, applicable to any interferometric detectors, for
detecting ringdown signals, for estimating black hole parameters from those
signals, and for testing the no-hair theorem of general relativity. Focusing on
LISA, we use current models of its sensitivity to compute the expected
signal-to-noise ratio for ringdown events, the relative parameter estimation
accuracy, and the resolvability of different modes. We also discuss the extent
to which uncertainties on physical parameters, such as the black hole spin and
the energy emitted in each mode, will affect our ability to do black hole
spectroscopy.

\\ ( http://arXiv.org/abs/gr-qc/0512160 , 436kb)


--------------------
"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
Guest_Richard Trigaux_*
post Jan 9 2006, 06:29 PM
Post #17





Guests






So that we shall be able to HEAR the black holes ringing when forming!!!

If black holes are related to gamma ray bursts, they may form eventually about one black hole per day in the observble universe. But, like the gamma ray bursts, they are very far.

Some thinking:

oscillation modes of black holes are gravitationnal waves which propagate around (or inward-out) the black hole. In order to emitt toward the outside, they must be near the horizon. Inner modes may not emitt outside the black hole. If basic black holes are about 10kms in diametre, a wave can turn around it at 10khz, or more.(this is not an exact calculus, just an order of magnitude)

Giant galactic black holes could eventually oscillate at much lower frequencies, when they swallow a star, for instance 0.01hz for a 10 million kms wide black hole. Intermediary frequencies would point at intermediary sized black holes.

I wait for hearing the sound, and wonder how many time a black hole may keep ringing before losing its energy. If this time is short, we shall hear like piano notes from time to time (although I don't expect that black holes harmonics are as pleasant as piano harmonics). If this time is in the order of some days, we may hear an everchanging cosmic chord, eventually nice.
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ljk4-1
post Jan 10 2006, 03:16 PM
Post #18


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Astrophysics, abstract
astro-ph/0601161

From: Clovis Hopman [view email]

Date: Mon, 9 Jan 2006 12:47:10 GMT (74kb)

Resonant relaxation near a massive black hole: the stellar distribution and gravitational wave sources

Authors: Clovis Hopman, Tal Alexander (Weizmann)

Comments: Submitted to ApJ

Resonant relaxation (RR) of orbital angular momenta occurs near massive black holes (MBHs) where the stellar orbits are nearly Keplerian and so do not precess significantly. The resulting coherent torques efficiently change the magnitude of the angular momenta and rotate the orbital inclination in all directions. As a result, many of the tightly bound stars very near the MBH are rapidly destroyed by falling into the MBH on low-angular momentum orbits, while the orbits of the remaining stars are efficiently randomized. We solve numerically the Fokker-Planck equation in energy for the steady state distribution of a single mass population with a RR sink term. We find that the steady state current of stars, which sustains the accelerated drainage close to the MBH, can be up to ~10 times larger than that due to non-coherent 2-body relaxation alone. RR mostly affects tightly bound stars, and so it increases only moderately the total tidal disruption rate, which is dominated by stars originating from less bound orbits farther away. We show that the event rate of gravitational wave (GW) emission from inspiraling stars, originating much closer to the MBH, is dominated by RR dynamics. The GW event rate depends on the uncertain efficiency of RR. The efficiency indicated by the few available simulations implies rates ~10 times higher than those predicted by 2-body relaxation, which would improve the prospects of detecting such events by future GW detectors, such as LISA. However, a higher, but still plausible RR efficiency can lead to the drainage of all tightly bound stars and strong suppression of GW events from inspiraling stars. We apply our results to the Galactic MBH, and show that the observed dynamical properties of stars there are consistent with RR.

http://arxiv.org/abs/astro-ph/0601161


--------------------
"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 10 2006, 05:34 PM
Post #19


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



Dewayne Washington
Goddard Space Flight Center, Greenbelt, Md. Jan. 9, 2006
(301) 286-0040

Release 06-03

SCIENTISTS FIND BLACK HOLE’S ‘POINT OF NO RETURN’

Scientists using NASA's Rossi X-ray Timing Explorer have compared suspected neutron stars and black holes and found that the black holes behaved as if each one has an event horizon, the theoretical border from beyond which nothing, not even light, can escape.

The team found that X-ray light emitted from these two types of regions behaved differently. As expected, the neutron stars appeared to have a hard surface, which erupts in an X-ray explosion every several hours. The black holes appeared to have no surface. Matter falling toward the black hole seems to disappear into the void.

Dr. Ron Remillard of the MIT Kavli Institute in Cambridge, Mass., led the analysis and discusses his team's result today at a press conference at the 207th meeting of the American Astronomical Society in Washington. His colleagues are Dacheng Lin of MIT and Randall Cooper and Prof. Ramesh Narayan of the Harvard-Smithsonian Center for Astrophysics in Cambridge.

"Event horizons are invisible by definition, so it seems impossible to prove their existence," said Remillard. "Yet by looking at dense objects that pull in gas, we can infer whether that gas crashes and accumulates onto a hard surface or just quietly vanishes. For the group of suspected black holes we studied, there is a complete absence of surface explosions called X-ray bursts. The gas that would fuel such bursts appears to vanish."

The rest of the story is here:

http://www.nasa.gov/centers/goddard/news/t...e_noreturn.html


Donna Weaver
Space Telescope Science Institute, Baltimore
(Phone: 410-338-4493)

Rogier Windhorst
Arizona State University, Tempe, Ariz.
(Phone: 480/965-7143)

RELEASE NO.: STScI-PR06-04

GALACTIC MERGERS HELP MONSTER BLACK HOLES GROW

An analysis of the Hubble Space Telescope's deepest view of the universe
offers compelling evidence that monster black holes in the centers of
galaxies were not born big but grew over time through repeated galactic
mergers. The Hubble Ultra Deep Field (HUDF) studies also confirm recent
computer simulations that predict that that newly merging galaxies are
enshrouded in so much dust that astronomers cannot see black holes
feasting on stars and gas from the mergers. The computer simulations,
as supported by Hubble, suggest that it takes hundreds of millions to a
billion years before enough dust clears so that astronomers can see the
black holes feasting on stars and gas from the merger.

For images and additional information about this research on the Web, visit:

http://hubblesite.org/news/2006/04.


--------------------
"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
ljk4-1
post Jan 11 2006, 04:36 PM
Post #20


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



QUOTE (ljk4-1 @ Jan 10 2006, 12:34 PM)
Donna Weaver
Space Telescope Science Institute, Baltimore
(Phone: 410-338-4493)

Rogier Windhorst
Arizona State University, Tempe, Ariz.
(Phone: 480/965-7143)

RELEASE NO.: STScI-PR06-04

GALACTIC MERGERS HELP MONSTER BLACK HOLES GROW

An analysis of the Hubble Space Telescope's deepest view of the universe
offers compelling evidence that monster black holes in the centers of
galaxies were not born big but grew over time through repeated galactic
mergers. The Hubble Ultra Deep Field (HUDF) studies also confirm recent
computer simulations that predict that that newly merging galaxies are
enshrouded in so much dust that astronomers cannot see black holes
feasting on stars and gas from the mergers. The computer simulations,
as supported by Hubble, suggest that it takes hundreds of millions to a
billion years before enough dust clears so that astronomers can see the
black holes feasting on stars and gas from the merger.

For images and additional information about this research on the Web, visit:

http://hubblesite.org/news/2006/04.
*


Paper: astro-ph/0601202

Date: Tue, 10 Jan 2006 11:27:42 GMT (542kb)

Title: Did Galaxy Assembly and Supermassive Black-Hole Growth go hand-in-hand?

Authors: R.A. Windhorst, S.H. Cohen, A.N. Straughn, R.E. Ryan Jr., N.P. Hathi,
R.A. Jansen (ASU), A.M. Koekemoer, N. Pirzkal, C. Xu, B. Mobasher, S.
Malhotra, L. Strolger & J.E. Rhoads (STScI)

Comments: 9 pages, Latex2e requires 'elsart' and 'elsart3' (included), 10
postscript figures. To appear in the Proceedings of the Leiden Workshop on
"QSO Host Galaxies: Evolution and Environment", eds. P.D. Barthel & D.B.
Sanders (New Astron. Rev., 2006)
\\
In this paper, we address whether the growth of supermassive black-holes has
kept pace with the process of galaxy assembly. For this purpose, we first
searched the Hubble Ultra Deep Field (HUDF) for "tadpole galaxies", which have
a knot at one end and an extended tail. They appear dynamically unrelaxed --
presumably early-stage mergers -- and make up ~6% of the field galaxy
population. Their redshift distribution follows that of field galaxies,
indicating that -- if tadpole galaxies are indeed dynamically young -- the
process of galaxy assembly generally kept up with the reservoir of field
galaxies as a function of epoch. Next, we present a search for HUDF objects
with point-source components that are optically variable (at the >~3.0 sigma
level) on timescales of weeks--months. Among 4644 objects to i_AB=28.0 mag (10 sigma), 45 have variable point-like components, which are likely weak AGN.
About 1% of all field objects show variability for 0.1 < z < 4.5, and their
redshift distribution is similar to that of field galaxies. Hence supermassive
black-hole growth in weak AGN likely also kept up with the process of galaxy
assembly. However, the faint AGN sample has almost no overlap with the tadpole
sample, which was predicted by recent hydrodynamical numerical simulations.
This suggests that tadpole galaxies are early-stage mergers, which likely
preceded the ``turn-on'' of the AGN component and the onset of visible
point-source variability by >~1 Gyr.

\\ ( http://arXiv.org/abs/astro-ph/0601202 , 542kb)


--------------------
"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 19 2006, 04:29 PM
Post #21


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From: NGC 5907
Member No.: 430



General Relativity and Quantum Cosmology, abstract
gr-qc/0508115

From: Francisco Lobo [view email]

Date (v1): Sun, 28 Aug 2005 15:44:25 GMT (149kb)
Date (revised v2): Wed, 31 Aug 2005 21:50:31 GMT (150kb)
Date (revised v3): Tue, 17 Jan 2006 23:41:56 GMT (152kb)

Stable dark energy stars

Authors: Francisco S. N. Lobo

Comments: 10 pages, 6 figures, Revtex4. V2: comments and references added, 11 pages. V3: Significant additions and clarifications, 12 pages

The gravastar picture is an alternative model to the concept of a black hole, where there is an effective phase transition at or near where the event horizon is expected to form, and the interior is replaced by a de Sitter condensate. In this work, a generalization of the gravastar picture is explored, by considering a matching of an interior solution governed by the dark energy equation of state, $\omega\equiv p/ \rho<-1/3$, to an exterior Schwarzschild vacuum solution at a junction interface. The motivation for implementing this generalization arises from the fact that recent observations have confirmed an accelerated cosmic expansion, for which dark energy is a possible candidate. Several relativistic dark energy stellar configurations are analyzed by imposing specific choices for the mass function.

The first case considered is that of a constant energy density, and the second choice, that of a monotonic decreasing energy density in the star's interior. The dynamical stability of the transition layer of these dark energy stars to linearized spherically symmetric radial perturbations about static equilibrium solutions is also explored. It is found that large stability regions exist that are sufficiently close to where the event horizon is expected to form, so that it would be difficult to distinguish the exterior geometry of the dark energy stars, analyzed in this work, from an astrophysical black hole.

http://arxiv.org/abs/gr-qc/0508115


--------------------
"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 20 2006, 04:03 PM
Post #22


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Group: Members
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From: NGC 5907
Member No.: 430



Paper: astro-ph/0601406

Date: Wed, 18 Jan 2006 22:55:01 GMT (734kb)

Title: Radiation Transport Around Kerr Black Holes

Authors: Jeremy D. Schnittman

Comments: PhD thesis in astrophysics from MIT; submitted on the occasion of the
first anniversary of my defense. 212 pp, 53 figs, 8 tables, uses
mitthesis.cls. For full-resolution version, see

http://hdl.handle.net/1721.1/30362
\\
This Thesis describes the basic framework and applications of a relativistic
ray-tracing code for analyzing accretion processes around Kerr black holes. We
begin in Chapter 1 with a brief historical summary of the major advances in
black hole astrophysics over the past few decades. In Chapter 2 we present a
detailed description of the ray-tracing code, which is used to calculate the
transfer function between the accretion disk and the detector. In Chapter 3, we
employ a simple ``hot spot'' model to explain the frequencies and amplitudes of
quasi-periodic oscillations (QPOs). In Chapter 4, we introduce additional
features to the hot spot model to explain the broadening of the QPO peaks as
well as the damping of higher-frequency harmonics in the power spectrum. In
Chapter 5 we present a description of the structure of a relativistic
alpha-disk around a Kerr black hole, and the observed spectrum from such a
disk. The features of this modified thermal spectrum may be used to infer the
physical properties of the accretion disk and the central black hole. In
Chapter 6 we develop a Monte Carlo code to calculate the detailed propagation
of photons from a hot spot emitter scattering through a corona surrounding the
black hole. The coronal scattering has two major observable effects: the
inverse-Compton process alters the photon spectrum by adding a high energy
power-law tail, and the random scattering of each photon effectively damps out
the highest frequency modulations in the X-ray light curve.

\\ ( http://arXiv.org/abs/astro-ph/0601406 , 734kb)


--------------------
"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 20 2006, 07:02 PM
Post #23


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Group: Members
Posts: 2454
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From: NGC 5907
Member No.: 430



Paper: astro-ph/0601450

Date: Thu, 19 Jan 2006 19:54:52 GMT (16kb)

Title: Upper limits on the central black hole masses of 47Tuc and NGC6397

Authors: S. De Rijcke, P. Buyle, H. Dejonghe

Comments: 4 pages, 1 figure, accepted for publication by MNRAS
\\
We present upper-limits on the masses of the putative central
intermediate-mass black holes in two nearby Galactic globular clusters: 47Tuc
(NGC104), the second brightest Galactic globular cluster, and NGC6397, a
core-collapse globular cluster and, with a distance of 2.7 kpc, quite possibly
the nearest globular cluster, using a technique suggested by T. Maccarone.
These mass estimates have been derived from 3sigma upper limits on the radio
continuum flux at 1.4 GHz, assuming that the putative central black hole
accretes the surrounding matter at a rate between 0.1% and 1% of the Bondi
accretion rate. For 47Tuc, we find a 3sigma upper limit of 2060 - 670 solar
masses, depending on the actual accretion rate of the black hole and the
distance to 47Tuc. For NGC6397, which is closer to us, we derive a 3sigma upper
limit of 1290 - 390 solar masses. While estimating mass upper-limits based on
radio continuum observations requires making assumptions about the gas density
and the accretion rate of the black hole, their derivation does not require
complex and time consuming dynamical modeling. Thus, this method offers an
independent way of estimating black hole masses in nearby globular clusters.
If, generally, central black holes in stellar systems accrete matter faster
than 0.1% of the Bondi accretion rate, then these results indicate the absence
of black holes in these globular clusters with masses as predicted by the
extrapolated M-sigma relation.

\\ ( http://arXiv.org/abs/astro-ph/0601450 , 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 Jan 31 2006, 09:27 PM
Post #24


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



Astrophysics, abstract
astro-ph/0601662

From: Leonid Verozub V [view email]

Date: Sun, 29 Jan 2006 15:26:51 GMT (142kb)

Sgr A* as probe of the theory of supermassive compact objects without event horizon

Authors: L. V. Verozub

Comments: Final version, Latex, 10 pages, 7 figure. Accepted to Astron. Nachr

In the present paper some consequences of the hypothesis that the supermassive compact object in the Galaxy centre relates to a class of objects without event horizon are examined. The possibility of the existence of such objects was substantiated by the author earlier. It is shown that accretion of a surrounding gas can cause nuclear combustion in the surface layer which, as a result of comptonization of the superincumbent hotter layer, may give a contribution to the observed Sgr A* radiation in the range $10^{15} \div 10^{20} Hz$.

It is found a contribution of the possible proper magnetic moment of the object to the observed synchrotron radiation on the basis of Boltzmann's equation for photons which takes into account the influence of gravity to their motion and frequency. We arrive at the conclusion that the hypothesis of the existence in the Galaxy centre of the object with such extraordinary gravitational properties at least does not contradict observations.

http://arxiv.org/abs/astro-ph/0601662


--------------------
"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 1 2006, 04:07 PM
Post #25


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



Astrophysics, abstract
astro-ph/0601705

From: Alberto Sesana [view email]

Date: Tue, 31 Jan 2006 13:38:22 GMT (53kb)

Hardening in a Time--Evolving Stellar Background: Hyper--Velocity Stars, Orbital Decay and Prediction for Lisa

Authors: F. Haardt (1), A. Sesana (1), P. Madau (2) ((1)Universita' dell'Insubria, Como, Italy,(2)University of California, Santa Cruz CA, USA)

Comments: 8 pages, 4 figures, to be published in the Proceedings of the workshop "AGN and Galaxy Evolution", Castel Gandolfo (Italy), 3-6 october, 2005

We study the long-term evolution of massive black hole binaries (MBHBs) at the centers of galaxies using detailed full three-body scattering experiments. Stars, drawn from a distribution unbound to the binary, are ejected by the gravitational slingshot. We quantify the effect of secondary slingshots -- stars returning on small impact parameter orbits to have a second super-elastic scattering with the MBHB -- on binary separation. Even in the absence of two-body relaxation or gas dynamical processes, very unequal mass binaries of mass M=10^7 solar masses can shrink to the gravitational wave emission regime in less than a Hubble time, and are therefore a target for the planned Laser Interferometer Space Antenna (LISA). Three-body interactions create a subpopulation of hypervelocity stars on nearly radial, corotating orbits, with a spatial distribution that is initially highly flattened in the inspiral plane of the MBHB, but becomes more isotropic with decreasing binary separation. The mass ejected is ~0.7 times the binary reduced mass, and most of the stars are ejected in an initial burst lasting much less than a bulge crossing time.

http://arxiv.org/abs/astro-ph/0601705


--------------------
"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 2 2006, 10:30 PM
Post #26


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Group: Members
Posts: 2454
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From: NGC 5907
Member No.: 430



Astrophysics, abstract
astro-ph/0602013

From: Massimo Dotti [view email]

Date: Wed, 1 Feb 2006 10:47:06 GMT (351kb)

Inspiral of double black holes in gaseous nuclear disks

Authors: M. Dotti M. Colpi F. Haardt

Comments: 3 pages, 2 figures, to be published in the Proceedings of the conference "Relativistic Astrophysics and Cosmology - Einstein's Legacy-", November 7-11 2005, Munich, Germany

We study the inspiral of double black holes orbiting inside a massive rotationally supported gaseous disk, with masses in the Laser Interferometer Space Antenna (LISA) window of detectability. Using high-resolution SPH simulations, we follow the black hole dynamics in the early phase when gas-dynamical friction acts on the black holes individually, and continue our simulation until the form a close binary. We find that in the early sinking the black holes loose memory of their initial orbital eccentricity if they co-rotate with the gaseous disk. As a consequence the massive black holes form a binary with very low eccentricity. During the inspiral, gravitational capture of gas by the black holes occurs mainly when they move on circular orbits and may ignite AGN activity: eccentric orbits imply instead high relative velocities and weak gravitational focusing.

http://arxiv.org/abs/astro-ph/0602013


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"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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- maryalien   Black Holes   Dec 7 2005, 04:04 PM
- - mike   Actually I think Hawking recently said that some i...   Dec 7 2005, 06:05 PM
- - Jeff7   ...which is why his field is theoretical physics.   Dec 7 2005, 07:19 PM
- - dvandorn   First, though it's likely redundant for most o...   Dec 7 2005, 08:20 PM
- - maryalien   i got the feeling i was out of my league when i re...   Dec 8 2005, 12:43 AM
|- - Richard Trigaux   QUOTE (maryalien @ Dec 8 2005, 12:43 AM)i got...   Dec 8 2005, 08:21 AM
- - maryalien   thank you for your explanations and time. i hope ...   Dec 8 2005, 11:49 AM
- - dvandorn   Mind? Of course not! That's what we do h...   Dec 8 2005, 01:52 PM
|- - ljk4-1   --- Thursday, December 1, 2005 --- =============...   Dec 8 2005, 02:14 PM
|- - Richard Trigaux   QUOTE (dvandorn @ Dec 8 2005, 01:52 PM)Mind? ...   Dec 8 2005, 02:14 PM
|- - Marcel   QUOTE (dvandorn @ Dec 8 2005, 01:52 PM)But, a...   Dec 8 2005, 02:30 PM
|- - Richard Trigaux   QUOTE (Marcel @ Dec 8 2005, 02:30 PM)As far a...   Dec 8 2005, 03:31 PM
||- - ljk4-1   Paper: astro-ph/0512194 Date: Wed, 7 Dec 2005 15:...   Dec 8 2005, 03:40 PM
|- - maryalien   QUOTE (Marcel @ Dec 8 2005, 02:30 PM)As far a...   Dec 10 2005, 01:18 PM
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