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maryalien
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
mike
Actually I think Hawking recently said that some information does remain intact in a black hole.

Personally though I'm not sure how anyone can really say what happens in a black hole, having never gone into one or even being especially close to one, so far as we can tell..
Jeff7
...which is why his field is theoretical physics.smile.gif
dvandorn
First, though it's likely redundant for most of the people here, let's talk some basics about black holes.

Black holes are all about the relationship between mass, energy and gravity. Gravity is a function of mass -- the more mass you have, the greater gravitational influence it has on surrounding masses.

Gravity even affects photons and other energy "particles." A black hole comes into being when a body has so much mass that any particle of mass or energy that approaches it would have to accelerate faster than the speed of light in order to escape it.

That would be relatively easy to understand, if it weren't for the predicted effects of special relativity. Einstein's classic E=MC^2 equation states the relationship between mass and energy -- that a given amount of energy (E) is equal to the square of a given amount of mass (M) traveling at the speed of light ©. That's been taken to mean, rather simplistically, that mass cannot be accelerated all the way to the speed of light, and if it were, it would transform entirely into energy.

More importantly, special relativity also states that the passage of time is relative to how fast you are traveling compared to another point in space. The faster you go, relative to a given point in space, the slower time passes for you -- again, relative to that other given point in space.

When any mass passes the point near a black hole where it would have to accelerate to lightspeed or beyond in order to escape, the black hole's gravity would theoretically accelerate any such mass beyond the speed of light. But since that's both impossible *and* the required effect of such strong gravity, what happens beyond that point is called a singularity -- it's a region of space where physics cannot describe or predict conditions. That line itself, beyond which no mass can escape, is called the event horizon -- since no information, not even photons, can come out from within that boundary and tell us anything about any events happening within.

As a mass approaches the event horizon and is suddenly accelerated to just short of lightspeed, the passage of time for that mass would slow to a near-stop. For us, observing from outside, time would pass normally and we would see time pass normally for the accelerated mass as it comes close to being swallowed -- but once again, if the matter is accelerated to or beyond lightspeed, then time passage for it ought to stop entirely, and our physics can't describe what happens to mass that's frozen in time (at least, relative to the outside universe). So, once again, we have a singularity -- we just cannot describe what happens to the mass, how it might behave, or anything.

For a long time, it was thought that black holes sucked everything in, and nothing, not even the smallest amount of information about the black hole within or the mass falling onto it, would be able to escape. But we've found out that there are basically two kinds of information that *can* escape from a back hole: whether or not it's rotating, and whether or not it's electrically charged (and what the charge is).

You can tell if a black hole is rotating because its gravity field rotates with it, and the gravity field is the only really major thing that extends beyond the event horizon. You can observe this gravity field by looking at the effect it has on objects near the black hole. A spinning gravitational field accelerates mass both towards the black hole and along the rotation vector, so you can see and measure the rate of spin. (Again, an interesting thing, since we're observing a time-passage-dependent effect, rotation, outside of a system within which Einsteinian physics states that the passage of time should have stopped.)

Charge is also detectable based on how masses behave near a black hole. I'm not as knowledgable as to how we can determine the charge, but I know it can be done.

Spinning black holes also radiate mass and energy -- well, the disk around them does, anyway. The spinning gravitational field smashes infalling matter and energy into an equatorial disk. As matter swirls down towards the black hole, some of it follows a trajectory that accelerates it away from the black hole. The way it works (I dont have the math to explain the effect, I've just seen the results), the mass sprayed away from the black hole is shot out in jets from the rotational poles. And so, a spinning black hole can have the appearance of a child's top -- a spinning, spiraling disk rotating around the vertical "stick" of polar jets. The black hole within, of course, is invisible.

There has got to be some way in which quantum physics and multi-dimensional physics will eventually be able to describe the conditions that exist within the event horizon of a black hole. But, as of right now, no theories exist that account for all the known facts -- or that answer most of the outstanding questions.

Oh, and one other thing -- black holes aren't forever. They lose mass very slowly over the course of time (something else that I don't have the math to explain properly), and after many billions of years, they can simply evaporate. However, the theories as to what happens when a black hole falls back below the mass required to maintain the singularity are pretty raw right now. It's possible that massive amounts of energy are released, but it's also possible that the singularity doesn't collapse immediately at the point where the mass falls below that critical level.

I'm sure there are others out there who can fill in anything I've missed, and correct me if I've made any faux pas, here... but I think that's a pretty good starting point for any discussion.

-the other Doug
maryalien
i got the feeling i was out of my league when i replied the first time, but your all so damned interesting, i love this stuff. really.

and i didnt know black holes diminish over time. i read an article saying that they vacillate, periods of "feeding" and dormancy. but naturally it must have its own life cycle, just like everything else and the universe...

thank you obe one
Richard Trigaux
QUOTE (maryalien @ Dec 8 2005, 12:43 AM)
i got the feeling i was out of my league when i replied the first time, but your all so damned interesting, i love this stuff.  really.

and i didnt know black holes diminish over time.  i read an article saying that they vacillate, periods of "feeding" and dormancy.  but naturally it must have its own life cycle, just like everything else and the universe...

thank you obe one
*



maryalien,

I think you are in the right place here, if you are interested by astronomy stuff. We are most of us professionnal scientists or "enlightened amateurs", so what we often speak of things other people cannot simply understand. Dvandorn was kind enough to explain you some basics, I think it is great.

Black holes do not go through periods of activity and dormancy, but, in the center of a galaxy, the activity of the galaxy sends matter at times to the black hole, and at other times it does not. So the black hole is "active" or not, depending on the feeding it receives. But basically it is still here, increasing at each feeding period and never decreasing.

Oh, some scientists postulated they decrease, but it is at a scale of time billins and billions times the age of the universe. So practically in astrophysics we consider they do not decrease.

An interesting fact is that the smaller a black hole is, the faster it decreases, with more and more energetic radiations. So than when a small black hole ends its life, it produces more and more energy, light, X ray, gamma rays, ending in something very much like a nuclear explosion (although no waste remain).
maryalien
thank you for your explanations and time. i hope from time to time no one will mind if i can ask a question or two.

mar
dvandorn
Mind? Of course not! That's what we do here.

By the way, I did a bit of research and got an explanation for the evaporation of black holes. It seems that there is a phenomenon known to exist in the cosmos called "vacuum fluctuations." Basically, what happens is that a pair of particles -- basically, a particle and an anti-particle, or in other words, matter and anti-matter -- can appear spontaneously in a vacuum. They immediately annihilate each other, so conservation of mass and energy is maintained. But for that instant, it is not. And it is that violation of the second law of thermodynamics that allows a black hole to evaporate.

You see, over the course of billions of billions of years, such a pair of particles will appear billions of times next to the event horizon of a black hole. One of the pair will be swallowed by the black hole, and the other will radiate away from the black hole. The effect is such that the mass of the particle that escapes is actually reduced from the mass of the black hole. Over billions of billions of years, this process will reduce the mass of a black hole down to zero.

But, as Richard says, that process takes many, many times longer than the cosmos has already existed. So, a vast majority of black holes haven't lost all that much mass, and it will take many billions of times longer than the Universe has already existed for most black holes to evaporate in this fashion. And since there is little data to constrain the upper or lower limits of the spontaneous particle creation/annihilation, it's hard to set an exact date by which all the black holes in the Universe will evaporate.

So -- in the final analysis, it's something that happens. But it happens so slowly, relatively speaking, that we don't have to worry too much about it.

-the other Doug
ljk4-1
--- Thursday, December 1, 2005 ---

===================================

** Perseus Cluster: Chandra Proves Black Hole Influence is Far Reaching

Scientists using NASA's Chandra X-ray Observatory have discovered
evidence of energetic plumes - particles that extend 300,000 light years
into a massive cluster of galaxies. The plumes are due to explosive
venting from the vicinity of a supermassive black hole, and they provide
dramatic new evidence of the influence a black hole can have over
intergalactic distances.

< http://chandra.harvard.edu/photo/2005/perseus/ >
Richard Trigaux
QUOTE (dvandorn @ Dec 8 2005, 01:52 PM)
Mind?  Of course not!  That's what we do here.

By the way, I did a bit of research and got an explanation for the evaporation of black holes.  It seems that there is a phenomenon known to exist in the cosmos called "vacuum fluctuations."  ....

-the other Doug
*



Yes it is.

An interesting thing is that, after many theories, very small black holes would appear at time of a very violent collision between two particles, either from cosmic rays or into particle accelerators. But such micro-black holes, being very small, disintegrate instantly.

What would be interesting would be to observe this phenomenon in particule accelerators. because at the time when the micro-black hole disintegrates, all what was "inside" gets out again. So it is an unique mean to obtain information from within a black hole, and it could reply to many questions about what happen into black holes:

-are the particules swallowed by the black hole still existing individually, or are-they reduced to a singularity? (mar, a singularity is not a "thing" or an object, it is a point, in the mathematical meaning of this word, where common laws are no more valid. Think to a rubber membrane that you push with a nail, without however punching through: the point at the tip of the nail has special geometrical properties, that you can discover if you try to draw lines, squares, triangles, etc... on the membrane around it).

The alternative to a complete singularity would be some very compressed state of matter having in gross the diametre allowed by he Heisenberg uncertainties. (Mar, the Heisenberg uncertainties are, after quantum theory, a fundamental limit on the knowledge we can have of the position or energy of a particle. Within this domain, the particle appears as something blurred). But in this case, there would be a very small domain into the black hole with a normal physics, normal causality law and normal flow of time.

-Is the physics into a black hole similar tou ours, or may a new physics appear, eventually different for each black hole?


I would add that Hawking certainly has answers to all these questions, but very few people can judge of the validity of his work today, and no physical experiment can be designed to test his theories, except the one above.
Marcel
QUOTE (dvandorn @ Dec 8 2005, 01:52 PM)
But, as Richard says, that process takes many, many times longer than the cosmos has already existed.  So, a vast majority of black holes haven't lost all that much mass, and it will take many billions of times longer than the Universe has already existed for most black holes to evaporate in this fashion.  And since there is little data to constrain the upper or lower limits of the spontaneous particle creation/annihilation, it's hard to set an exact date by which all the black holes in the Universe will evaporate.

So -- in the final analysis, it's something that happens.  But it happens so slowly, relatively speaking, that we don't have to worry too much about it.

-the other Doug
*

As far as i know, singularities can exist in a variety of "sizes" and the time it takes for a black hole to evaporate by means of "Hawkins radiation (particles, antiparticles and gamma radiation) depends on it's mass. The lighter a black hole is, the faster it evaporates. Black holes that reside in galaxies (the 1 billion solar mass ones) theoretically take 10 to the 73 years to evaporate. However, there's theoretical evidence that smaller black holes (even as tiny as the Planck length) exist as well and they evaporate in very short times (instantly that is).

A question that keeps me curious about this theory is: if there's radiation coming from a black hole in the form of particles, antiparticles and gamma radiation (which has a speed of 300000 kms/hour), there must be other forms of radiation (the long searched gravity waves that is thought to escape from neutronstar-pairs ?) that can make its way from the event horizon. Why should gamma radiation make it, while other wavelengths cannot ?

Great explanation "other Doug' !
Richard Trigaux
QUOTE (Marcel @ Dec 8 2005, 02:30 PM)
As far as i know, singularities can exist in a variety of "sizes" ...
*


No, the singularity itself has no size; it is just a point (if singularities exist, there is no evidence of this). But it has a mass, and around it, a zone from where no information can come, so that from far it looks like a completelly black sphere. This sphere is called the event horizon, as nothing can be seen beyond. For a star sized black hole, its diametre is about some kilometres.

Yes, gravitation waves can come from a black hole, but only in the case when it is disturbed by a shock, for instance when two black holes merge to make only one: the resulting black hole vibrates and emits gravitation waves, until it dissipates its vibration energy and cease emitting, exactly like a guitar chord.


You meant 10 power 73 years, an amazing number indeed.
1000000000000000000000000000000000000000000000000000000000000000000000000 years.

A rotating black hole can also make rotate surrounding objects. A relevant analogy (not only an analogy, there are common mathematical laws) is with a transformer: the primary current creates a secondary current. So that a rotating black hole tugs the surrounding space. And, very like much in a transformer, the phenomenon is reversible: the matter outside the black hole can brake it, or in some instances accelerate it.
ljk4-1
Paper: astro-ph/0512194

Date: Wed, 7 Dec 2005 15:53:31 GMT (29kb)

Title: Constraints on Alternatives to Supermassive Black Holes

Authors: M. Coleman Miller (University of Maryland)

Comments: 5 pages including 1 figure, accepted by MNRAS
\\
Observations of the centers of galaxies continue to evolve, and it is useful
to take a fresh look at the constraints that exist on alternatives to
supermassive black holes at their centers. We discuss constraints complementary
to those of Maoz (1998) and demonstrate that an extremely wide range of other
possibilities can be excluded. In particular, we present the new argument that
for the velocity dispersions inferred for many galactic nuclei, even binaries
made of point masses cannot stave off core collapse because hard binaries are
so tight that they merge via emission of gravitational radiation before they
can engage in three-body or four-body interactions. We also show that under
these conditions core collapse leads inevitably to runaway growth of a central
black hole with a significant fraction of the initial mass, regardless of the
masses of the individual stars. For clusters of noninteracting low-mass objects
(from low-mass stars to elementary particles), relaxation of stars and compact
objects that pass inside the dark region will be accelerated by interactions
with the dark mass. If the dark region is instead a self-supported object such
as a fermion ball, then if stellar-mass black holes exist they will collide
with the object, settle, and consume it. The net result is that the keyhole
through which alternatives to supermassive black holes must pass is
substantially smaller and more contrived than it was even a few years ago.

\\ ( http://arXiv.org/abs/astro-ph/0512194 , 29kb)
maryalien
QUOTE (Marcel @ Dec 8 2005, 02:30 PM)
As far as i know, singularities can exist in a variety of "sizes" and the time it takes for a black hole to evaporate by means of "Hawkins radiation (particles, antiparticles and gamma radiation) depends on it's mass. The lighter a black hole is, the faster it evaporates. Black holes that reside in galaxies (the 1 billion solar mass ones) theoretically take 10 to the 73 years to evaporate. However, there's theoretical evidence that smaller black holes (even as tiny as the Planck length) exist as well and they evaporate in very short times (instantly that is).

A question that keeps me curious about this theory is: if there's radiation coming from a black hole in the form of particles, antiparticles and gamma radiation (which has a speed of 300000 kms/hour), there must be other forms of radiation (the long searched gravity waves that is thought to escape from neutronstar-pairs ?) that can make its way from the event horizon. Why should gamma radiation make it, while other wavelengths cannot ?

Great explanation "other Doug' !
*


wasnt there a nasa presentation about GRB's and solving their mystery? i saw it in another forum but couldnt find an update as of yet. does this tie in? mar
ljk4-1
Paper: astro-ph/0512241

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

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

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

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

\\ ( http://arXiv.org/abs/astro-ph/0512241 , 23kb)
ljk4-1
Paper: astro-ph/0512241

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

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

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

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

\\ ( http://arXiv.org/abs/astro-ph/0512241 , 23kb)
Richard Trigaux
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
ljk4-1
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)
ljk4-1
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)
ljk4-1
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)
ljk4-1
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)
ljk4-1
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)
ljk4-1
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)
ljk4-1
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
nprev
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.
ljk4-1
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)
ljk4-1
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)
Richard Trigaux
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.
ljk4-1
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)
ljk4-1
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
ljk4-1
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)
Richard Trigaux
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.
ljk4-1
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
ljk4-1
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.
ljk4-1
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)
ljk4-1
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
ljk4-1
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)
ljk4-1
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)
ljk4-1
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
ljk4-1
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
ljk4-1
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
ljk4-1
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)
ljk4-1
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.
ljk4-1
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
ljk4-1
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
ljk4-1
Astrophysics, abstract
astro-ph/0602307

From: Rob Fender [view email]

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

A transient relativistic radio jet from Cygnus X-1

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

Comments: Accepted for publication in MNRAS

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

http://arxiv.org/abs/astro-ph/0602307
ljk4-1
Astrophysics, abstract
astro-ph/0602363

From: Mitchell C. Begelman [view email]

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

Formation of Supermassive Black Holes by Direct Collapse in Pregalactic Halos

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

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

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

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

http://arxiv.org/abs/astro-ph/0602363
ljk4-1
DEEP X-RAY SURVEYS REVEAL BLACK HOLE POPULATION
-----------------------------------------------

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

http://spaceflightnow.com/news/n0602/21blackholes/
ljk4-1
Astrophysics, abstract
astro-ph/0603761

From: Pedro Gonzalez-Diaz [view email]

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

Will black holes eventually engulf the universe?

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

Comments: 4 pages, RevTex

Report-no: IMAFF-RCA-06-04

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

http://arxiv.org/abs/astro-ph/0603761
ljk4-1
Spacecraft may be able to determine if braneworld black holes exist right
in our Sol system.


Scientists Predict How to Detect a Fourth Dimension of Space

New theory of gravity challenges Einstein's general relativity

Thursday, May 25, 2006

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

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

...

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

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

Full article here:

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