IPB

Welcome Guest ( Log In | Register )

4 Pages V  < 1 2 3 4 >  
Reply to this topicStart new topic
Black Holes
ljk4-1
post Jan 9 2006, 04:03 PM
Post #31


Senior Member
****

Group: Members
Posts: 2454
Joined: 8-July 05
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

Go to the top of the page
 
+Quote Post
Guest_Richard Trigaux_*
post Jan 9 2006, 06:29 PM
Post #32





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.
Go to the top of the page
 
+Quote Post
ljk4-1
post Jan 10 2006, 03:16 PM
Post #33


Senior Member
****

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



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

Go to the top of the page
 
+Quote Post
ljk4-1
post Jan 10 2006, 05:34 PM
Post #34


Senior Member
****

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

Go to the top of the page
 
+Quote Post
ljk4-1
post Jan 11 2006, 04:36 PM
Post #35


Senior Member
****

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

Go to the top of the page
 
+Quote Post
ljk4-1
post Jan 19 2006, 04:29 PM
Post #36


Senior Member
****

Group: Members
Posts: 2454
Joined: 8-July 05
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

Go to the top of the page
 
+Quote Post
ljk4-1
post Jan 20 2006, 04:03 PM
Post #37


Senior Member
****

Group: Members
Posts: 2454
Joined: 8-July 05
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

Go to the top of the page
 
+Quote Post
ljk4-1
post Jan 20 2006, 07:02 PM
Post #38


Senior Member
****

Group: Members
Posts: 2454
Joined: 8-July 05
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

Go to the top of the page
 
+Quote Post
ljk4-1
post Jan 31 2006, 09:27 PM
Post #39


Senior Member
****

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

Go to the top of the page
 
+Quote Post
ljk4-1
post Feb 1 2006, 04:07 PM
Post #40


Senior Member
****

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

Go to the top of the page
 
+Quote Post
ljk4-1
post Feb 2 2006, 10:30 PM
Post #41


Senior Member
****

Group: Members
Posts: 2454
Joined: 8-July 05
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


--------------------
"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

Go to the top of the page
 
+Quote Post
ljk4-1
post Feb 3 2006, 04:18 PM
Post #42


Senior Member
****

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



Paper: astro-ph/0602029

Date: Thu, 2 Feb 2006 20:02:50 GMT (217kb)

Title: Multi-scale simulations of merging galaxies with supermassive black
holes

Authors: Lucio Mayer (ETH Zurich), Stelios Kazantzidis (KICP Chicago), Piero
Madau (UC Santa Cruz), Monica Colpi (Universita' Milano-Bicocca), Thomas
Quinn (University of Washington), James Wadsley (McMaster University)

Comments: 7 pages, 3 Figures, extended version of the contributed paper to
appear in the Proceedings of the Conference "Relativistic Astrophysics and
Cosmology - Einstein's Legacy" held in Munich, Germany, November 7-12 2005
\\
We present the results of the first multi-scale N-Body+SPH simulations of
merging galaxies containing central supermassive black holes (SMBHs) and having
a spatial resolution of only a few parsecs. Strong gas inflows associated with
equal-mass mergers produce non-axisymmetric nuclear disks with masses of order
$10^9 M_{\odot}$, resolved by about $10^6$ SPH particles. Such disks have sizes
of several hundred parsecs but most of their mass is concentrated within less
than $50$ pc. We find that a close SMBH pair forms after the merger. The
separation of the two SMBHs then shrinks further owing to dynamical friction
against the predominantly gaseous background. The orbits of the SMBHs decay
down to the minimum resolvable scale in a few million years for an ambient gas
temperature and density typical of a region undergoing a starburst. These
results suggest the initial conditions necessary for the eventual coalescence
of the two holes arise naturally from the merging of two equal-mass galaxies
whose structure and orbits are consistent with the predictions of the
$\Lambda$CDM model. Our findings have important implications for planned
gravitational wave detection experiments such as {\it LISA}.

\\ ( http://arXiv.org/abs/astro-ph/0602029 , 217kb)


Paper: astro-ph/0602043

Date: Thu, 2 Feb 2006 13:58:56 GMT (21kb)

Title: The Source of Mass Accreted by the Central Black Hole in Cooling Flow
Clusters

Authors: Noam Soker (Technion, Israel)

Comments: Submitted to MNRAS
\\
This paper reports the study of the cold-feedback heating in cooling flow
clusters. In the cold-feedback model the mass accreted by the central black
hole originates in non-linear over-dense blobs of gas residing in an extended
region (r ~ 5-30 kpc); these blobs are originally hot, but then cool faster
than their environment and sink toward the center. The intra-cluster medium
(ICM) entropy profile must be shallow for the blobs to reach the center as cold
blobs. I build a toy model to explore the role of the entropy profile and the
population of dense blobs in the cold-feedback mechanism. The mass accretion
rate by the central black hole is determined by the cooling time of the ICM,
the entropy profile, and the presence of inhomogeneities. The mass accretion
rate determines the energy injected by the black hole back to the ICM. These
active galactic nucleus (AGN) outbursts not only heat the ICM, but also change
the entropy profile in the cluster and cause inhomogeneities that are the seeds
of future dense blobs. Therefore, in addition to the ICM temperature (or
energy), the ICM entropy profile and ICM inhomogeneities are also ingredients
in the feedback mechanism.

\\ ( http://arXiv.org/abs/astro-ph/0602043 , 21kb)


Paper: astro-ph/0602047

Date: Thu, 2 Feb 2006 19:16:54 GMT (223kb)

Title: Strangeness in Compact Stars

Authors: Fridolin Weber (San Diego State University), Andreu Torres i Cuadrat
(Universitat Autonoma de Barcelona), Alexander Ho (San Diego State
University), Philip Rosenfield (San Diego State University)

Comments: 26 pages, 13 figures, 29th Johns Hopkins Workshop on current problems
in particle theory: Strong Matter in the Heavens
\\
Astrophysicists distinguish between three different types of compact stars.
These are white dwarfs, neutron stars, and black holes. The former contain
matter in one of the densest forms found in the Universe. This feature,
together with the unprecedented progress in observational astronomy, makes such
stars superb astrophysical laboratories for a broad range of exciting physical
studies. This article studies the role of strangeness for compact star
phenomenology. Strangeness is carried by hyperons, mesons, H-dibaryons, and
strange quark matter, and may leave its mark in the masses, radii, cooling
behavior, surface composition and the spin evolution of compact stars.

\\ ( http://arXiv.org/abs/astro-ph/0602047 , 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

Go to the top of the page
 
+Quote Post
ljk4-1
post Feb 6 2006, 07:43 PM
Post #43


Senior Member
****

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



LOOKING FOR BLACK HOLES IN THE ATMOSPHERE is one of the prominent
missions for the newly built Pierre Auger Observatory. Black holes
can arise from the collapse of heavy stars but might also, according
to theoretical particle physics, be produced when cosmic ray
particles (especially neutrinos) with multi-TeV energies pass very
close to a particle within our atmosphere. The ensuing air shower
of secondary particles would be sensed on the ground in Auger's huge
array of detectors, which began their work in 2003 (see figure at
www.aip.org/png ). A new analysis of this hypothetical black hole
production process, however, questions whether many such
mini-black-hole events would occur. According to Dejan Stokovic
(Case Western Reserve University) and his colleagues, the same
process that encourages black hole creation in cosmic-ray neutrino
scattering events at the TeV energy level (rather than at the
impossibly inaccessible 10^19-GeV level, referred to as the Planck
energy) also should hasten the decay of protons to an extent not
seen in experiments designed to look for them. Therefore, Stokovic
(dejan@balin.phys.cwru.edu) argues, the robust stability of the
proton militates against an expected mini-black-hole production of
several hundred events over the Auger Observatory's active period
from 2003 to 2008. This doesn't necessarily mean that no black hole
events would seen, but probably not as many as were once
anticipated. (Stojkovic et al., Physical Review Letters, 3 February
2006)

***********
PHYSICS NEWS UPDATE is a digest of physics news items arising
from physics meetings, physics journals, newspapers and
magazines, and other news sources. It is provided free of charge
as a way of broadly disseminating information about physics and
physicists. For that reason, you are free to post it, if you like,
where others can read it, providing only that you credit AIP.
Physics News Update appears approximately once a week.


--------------------
"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

Go to the top of the page
 
+Quote Post
ljk4-1
post Feb 10 2006, 03:39 PM
Post #44


Senior Member
****

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



General Relativity and Quantum Cosmology, abstract
gr-qc/0602026

From: Michael Koppitz [view email]

Date (v1): Tue, 7 Feb 2006 20:48:32 GMT (311kb)
Date (revised v2): Thu, 9 Feb 2006 21:05:38 GMT (311kb)

Binary black hole merger dynamics and waveforms

Authors: John G. Baker, Joan Centrella, Dae-Il Choi, Michael Koppitz, James van Meter

Comments: 11 pages, 11 figures, submitted to PRD, update citations, minor changes

We study dynamics and radiation generation in the last few orbits and merger of a binary black hole system, applying recently developed techniques for simulations of moving black holes. Our analysis of the gravitational radiation waveforms and dynamical black hole trajectories produces a consistent picture for a set of simulations with black holes beginning on circular-orbit trajectories at a variety of initial separations. We find profound agreement at the level of one percent among the simulations for the last orbit, merger and ringdown. We are confident that this part of our waveform result accurately represents the predictions from Einstein's General Relativity for the final burst of gravitational radiation resulting from the merger of an astrophysical system of equal-mass non-spinning black holes. The simulations result in a final black hole with spin parameter a/m=0.69. We also find good agreement at a level of roughly 10 percent for the radiation generated in the preceding few orbits.

http://arxiv.org/abs/gr-qc/0602026


--------------------
"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

Go to the top of the page
 
+Quote Post
ljk4-1
post Feb 15 2006, 02:44 PM
Post #45


Senior Member
****

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



Life inside a black hole

NewScientist (subscription required) Feb. 10, 2006

*************************

There is a way for you to live
inside a black hole: find one that
has five dimensions. In the 4D case,
you would experience "tidal" forces
that vary so vastly over short
distances that your body would be
pulled apart. But in the 5D case,
there is no physical plughole, and
the tidal forces are negligible, so
you could happily explore without...

http://www.kurzweilai.net/email/newsRedire...sID=5295&m=7610


--------------------
"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

Go to the top of the page
 
+Quote Post

4 Pages V  < 1 2 3 4 >
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 16th August 2018 - 07:27 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.