Black Holes |
Black Holes |
Dec 7 2005, 04:04 PM
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#1
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Newbie Group: Members Posts: 8 Joined: 6-December 05 Member No.: 599 |
any one wanna talk black holes. i'm not a professional or anything. i vaguely remember hearing s. hawkin revising his opinion on it saying it wasnt a "worm hole" anymore and that it just destroys all matter and worth nothing else.
i only make my observations, childlike actually, to that of what happens on earth, and why shouldnt it happen in the rest of the universe. why should anything here (goverening law of physics, etc.) be different anywhere else? just like a tornado, or water running down a drain (or that infamous lake that was drained by accident by some guys drilling and all the water drained into the salt mine, i cant remember the name now but a 6 inch hole sucked in a tanker), why wouldnt a black hole be that "event" that punched a hole into another "dimension/galaxy whatever" with less pressure. and maybe all that "dark matter" is the "reminant" of what comes out of a black hole. i dont know, just talking. my head is always "out there, out of earth..." maryalien |
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Guest_Richard Trigaux_* |
Dec 12 2005, 04:24 PM
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#2
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Guests |
An intriguing thing about black hole evaporation is as follows.
As Hawking stated, a black hole may elit a black body-like thermal electromagnetic radiation, becomming hotter and hotter when the black hole becomes smaller. But if so, what become the electric charge and the baryonic number* of the black hole? In order to decay, a black hole has to emit also protons and electrons. The same process Hawking described allows for emission of protons and electrons too, but what is said about this? A black hole with a mass LESS than allowed by its baryonic number (its equivalent mass in hydrogen) need to receive energy to emit protons, and if it emits only protons, its electric charge will become so enormous that it will mandatorily call back any emitted particle. *baryonic number is a fundamental constant of quantum physics, which is 1 for the proton and any other particle of the same family of 16 (neutron, hyperon, etc...) and -1 for the corresponding anti-particules. In any nuclear reaction, the baryonic number cannot change, and this sets the possible and impossible reactions. The baryonic number of a potato is the number of protons and neutrons it contains. In order to go to a fully rationalized metric system, grocers should price potatoes after their baryonic number rather than their mass. |
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Dec 12 2005, 05:40 PM
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#3
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
Paper: astro-ph/0512211
Date: Thu, 8 Dec 2005 01:21:59 GMT (429kb) Title: On The Nature of the Compact Dark Mass at the Galactic Center Authors: Avery E. Broderick (1) and Ramesh Narayan (1,2) ((1) Institute for Theory and Computation, (2) Harvard University) Comments: 6 pages, 2 figures, submitted to ApJ Letters \\ We consider a model in which Sgr A*, the 3.5x10^6 M_sun supermassive black hole candidate at the Galactic Center, is a compact object with a surface. Given the very low quiescent luminosity of Sgr A* in the near infrared, the existence of a hard surface, even in the limit in which the radius approaches the horizon, places severe constraints upon the steady mass accretion rate in the source, requiring dM/dt < 10^-12 M_sun/yr. This limit is well below the minimum accretion rate needed to power the observed submillimeter luminosity of Sgr A*. We thus argue that Sgr A* does not have a surface, i.e., it must have an event horizon. The argument could be made more restrictive by an order of magnitude with microarcsecond resolution imaging, e.g., with submillimeter VLBI. \\ ( http://arXiv.org/abs/astro-ph/0512211 , 429kb) -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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Dec 16 2005, 05:44 AM
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#4
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
Paper: astro-ph/0512350
Date: Tue, 13 Dec 2005 23:58:06 GMT (110kb) Title: Supermassive Black Holes at the Center of Galaxies Authors: Christopher J. Greenwood Comments: 11 pages, 3 figures \\ This was my final paper for the AST 308 Galaxies class at Michigan State University. Using many sources I was able to compile a moderate amount of information concerning the evidence for, and the formation of Supermassive Black Holes. \\ ( http://arXiv.org/abs/astro-ph/0512350 , 110kb) -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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Dec 16 2005, 05:46 AM
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#5
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
Paper: astro-ph/0512358
Date: Wed, 14 Dec 2005 09:58:30 GMT (34kb) Title: GRB 050911: a black hole - neutron star merger or a naked GRB Authors: K.L. Page (1), A.R. King (1), A.J. Levan (2), P.T. O'Brien (1), J.P Osborne (1), S.D. Barthelmy (5), A.P. Beardmore (1), D.N. Burrows (3), S. Campana (4), N. Gehrels (5), J. Graham (6), M.R. Goad (1), O. Godet (1), Y. Kaneko (7), J.A. Kennea (3), C.B. Markwardt (5), D.E. Reichart (8), T. Sakamoto (5) & N.R. Tanvir (2) ((1) University of Leicester; (2) University of Hertfordshire; (3) PSU; (4) Osservatorio di Brera, Merate; (5) GSFC; (6)STScI; (7) NSSTC; (8) University of North Carolina) Comments: 4 pages using emulateapj; 2 figures. Accepted for publication in ApJ Letters \\ GRB 050911, discovered by the Swift Burst Alert Telescope, was not seen 4.6 hr later by the Swift X-ray Telescope, making it one of the very few X-ray non-detections of a Gamma-Ray Burst (GRB) afterglow at early times. The gamma-ray light-curve shows at least three peaks, the first two of which (~T_0 - 0.8 and T_0 + 0.2 s, where T_0 is the trigger time) were short, each lasting 0.5 s. This was followed by later emission 10-20 s post-burst. The upper limit on the unabsorbed X-ray flux was 1.7 x 10^-14 erg cm^-2 s^-1 (integrating 46 ks of data taken between 11 and 18 September), indicating that the decay must have been rapid. All but one of the long bursts detected by Swift were above this limit at ~4.6 hr, whereas the afterglows of short bursts became undetectable more rapidly. Deep observations with Gemini also revealed no optical afterglow 12 hr after the burst, down to r=24.0 (5-sigma limit). We speculate that GRB 050911 may have been formed through a compact object (black hole-neutron star) merger, with the later outbursts due to a longer disc lifetime linked to a large mass ratio between the merging objects. Alternatively, the burst may have occured in a low density environment, leading to a weak, or non-existent, forward shock - the so-called 'naked GRB' model. \\ ( http://arXiv.org/abs/astro-ph/0512358 , 34kb) Paper: astro-ph/0512344 Date: Tue, 13 Dec 2005 21:05:40 GMT (212kb) Title: Hypervelocity intracluster stars ejected by supermassive black hole binaries Authors: Kelly Holley-Bockelmann, Steinn Sigurdsson, J. Christopher Mihos, John J. Feldmeier, Robin Ciardullo, and Cameron McBride Comments: 4 pages, 3 color figures. Submitted to ApJ Letters \\ Hypervelocity stars have been recently discovered in the outskirts of galaxies, such as the unbound star in the Milky Way halo, or the three anomalously fast intracluster planetary nebulae (ICPNe) in the Virgo Cluster. These may have been ejected by close 3-body interactions with a binary supermassive black hole (SMBBH), where a star which passes within the semimajor axis of the SMBBH can receive enough energy to eject it from the system. Stars ejected by SMBBHs may form a significant sub-population with very different kinematics and mean metallicity than the bulk of the intracluster stars. The number, kinematics, and orientation of the ejected stars may constrain the mass ratio, semimajor axis, and even the orbital plane of the SMBBH. We investigate the evolution of the ejected debris from a SMBBH within a clumpy and time-dependent cluster potential using a high resolution, self-consistent cosmological N-body simulation of a galaxy cluster. We show that the predicted number and kinematic signature of the fast Virgo ICPNe is consistent with 3-body scattering by a SMBBH with a mass ratio $10:1$ at the center of M87. \\ ( http://arXiv.org/abs/astro-ph/0512344 , 212kb) -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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Dec 20 2005, 03:40 PM
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#6
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
Paper: astro-ph/0512455
Date: Sat, 17 Dec 2005 09:03:45 GMT (15kb) Title: Feedback Limits Rapid Growth of Seed Black Holes at High Redshift Authors: J.-M. Wang (1), Y.-M. Chen (1) and C. Hu (2,1) (1 IHEP, Beijing, 2 NAOC, Beijing) Comments: 4 pages in emulateapj5.sty, 1 color figure. to appear in The Astrophysical Journal Letters \\ Seed black holes formed in the collapse of population III stars have been invoked to explain the presence of supermassive black holes at high redshift. It has been suggested that a seed black hole can grow up to $10^{5\sim 6}\sunm$ through highly super-Eddington accretion for a period of $\sim 10^{6\sim 7}$ yr between redshift $z=20\sim 24$. We studied the feedback of radiation pressure, Compton heating and outflow during the seed black hole growth. It is found that its surrounding medium fueled to the seed hole is greatly heated by Compton heating. For a super-critical accretion onto a $10^3\sunm$ seed hole, a Compton sphere (with a temperature $\sim 10^6$K) forms in a timescale of $1.6\times 10^3$yr so that the hole is only supplied by a rate of $10^{-3}$ Eddington limit from the Compton sphere. Beyond the Compton sphere, the kinetic feedback of the strong outflow heats the medium at large distance, this leads to a dramatical decrease of the outer Bondi accretion onto the black hole and avoid the accumulation of the matter. The highly super-critical accretion will be rapidly halted by the strong feedback. The seed black holes hardly grow up at the very early universe unless the strong feedback can be avoided. \\ ( http://arXiv.org/abs/astro-ph/0512455 , 15kb) -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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Dec 22 2005, 04:41 PM
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#7
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
Paper: astro-ph/0512515
Date: Wed, 21 Dec 2005 00:18:33 GMT (183kb) Title: A size of ~1 AU for the radio source Sgr A* at the centre of the Milky Way Galaxy Authors: Zhi-Qiang Shen, K. Y. Lo, M.-C. Liang, Paul T. P. Ho, J.-H. Zhao Comments: 18 pages, 4 figures Journal-ref: Nature, 438(2005)62 \\ Although it is widely accepted that most galaxies have supermassive black holes (SMBHs) at their centers^{1-3}, concrete proof has proved elusive. Sagittarius A* (\sgras)^4, an extremely compact radio source at the center of our Galaxy, is the best candidate for proof^{5-7}, because it is the closest. Previous Very Long Baseline Interferometry (VLBI) observations (at 7mm) have detected that \sgras is ~2 astronomical unit (AU) in size^8, but this is still larger than the "shadow" (a remarkably dim inner region encircled by a bright ring) arising from general relativistic effects near the event horizon^9. Moreover, the measured size is wavelength dependent^{10}. Here we report a radio image of \sgras at a wavelength of 3.5mm, demonstrating that its size is $\sim$1 AU. When combined with the lower limit on its mass^{11}, the lower limit on the mass density is 6.5x10^{21} Msun pc^{-3}, which provides the most stringent evidence to date that \sgras is an SMBH. The power-law relationship between wavelength and intrinsic size (size $\propto$ wavelength^{1.09}), explicitly rules out explanations other than those emission models with stratified structure, which predict a smaller emitting region observed at a shorter radio wavelength. \\ ( http://arXiv.org/abs/astro-ph/0512515 , 184kb) -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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Dec 23 2005, 05:08 PM
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#8
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
Paper (*cross-listing*): hep-th/0512268
Date: Wed, 21 Dec 2005 11:04:12 GMT (16kb) Title: A fluid of black holes at the beginning of the Universe Authors: P. Diaz, M.A. Per, A.Segui Comments: Talk given at TAUP 2005, Zaragoza, Spain, 10-14 Sep 2005 \\ The most entropic fluid can be related to a dense gas of black holes that we use to study the beginning of the universe. We encounter difficulties to compatibilize an adiabatic expansion with the growing area for the coalescence of black holes. This problem may be circumvented for a quantum black hole fluid, whose classical counterpart can be described by a percolating process at the critical point. This classical regime might be related to the energy content of the current universe. \\ ( http://arXiv.org/abs/hep-th/0512268 , 16kb) -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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Dec 26 2005, 06:40 PM
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#9
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
Just in case anyone is wondering what a Black Holes topic is doing in the Voyager section:
http://www.patrawlings.com/images/large/S140.jpg -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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Dec 27 2005, 02:18 AM
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#10
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Merciless Robot Group: Admin Posts: 8785 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
QUOTE (ljk4-1 @ Dec 26 2005, 11:40 AM) Just in case anyone is wondering what a Black Holes topic is doing in the Voyager section: http://www.patrawlings.com/images/large/S140.jpg ...did the other Voyager acquire that image? Very clever. -------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Dec 30 2005, 05:27 PM
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#11
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
Paper: astro-ph/0512621
Date: Tue, 27 Dec 2005 18:24:40 GMT (91kb) Title: Astrometric Monitoring of Stellar Orbits at the Galactic Center with a Next Generation Large Telescope Authors: Nevin N. Weinberg (1, 2), Milos Milosavljevic (1), Andrea M. Ghez (3) ((1) Caltech, (2) KITP, (3) UCLA) Comments: 8 pages, 3 figures. ASP Conf. Series "Astrometry in the Age of the Next Generation of Large Telescopes", 2005, v.338, eds. P. Kenneth Seidelmann and Alice K. B. Monet Journal-ref: ASP Conf. Proc. 338 (2005) 252 \\ We show that with a Next Generation Large Telescope one can detect the accelerated motions of ~100 stars orbiting the massive black hole at the Galactic center. The positions and velocities of these stars will be measured to astrometric and spectroscopic precision several times better than currently attainable enabling detailed measurements of the gravitational potential in the neighborhood of the massive black hole. We show that the monitoring of stellar motions with such a telescopes enables: (1) a measurement of the Galactic center distance R_0 to better than 0.1% accuracy, (2) a measurement of the extended matter distribution near the black hole, including that of the exotic dark matter, (3) a detection of general relativistic effects due to the black hole including the prograde precession of stars and possibly the black hole spin, and (4) a detection of gravitational encounters between monitored stars and stellar remnants that accumulate near the Galactic center. Such encounters probe the mass function of the remnants. \\ ( http://arXiv.org/abs/astro-ph/0512621 , 91kb) -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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Dec 30 2005, 05:33 PM
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#12
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
Paper: astro-ph/0512625
Date: Wed, 28 Dec 2005 10:22:34 GMT (861kb) Title: Flares of Sagittarius a* at Millimeter Wavelengths Authors: Atsushi Miyazaki, Takahiro Tsutsumi, Makoto Miyoshi, Masato Tsuboi, Zhi-Qiang Shen Comments: 4 pages. Presented at the XXVIIIth Geleral Assembly of the URSI, Oct 2005, India \\ We have performed monitoring observations of the flux density toward the Galactic center compact radio source, Sagittarius A* (Sgr A*), which is a supermassive black hole, from 1996 to 2005 using the Nobeyama Millimeter Array of the Nobeyama Radio Observatory, Japan. These monitoring observations of Sgr A* were carried out in the 3- and 2-mm (100 and 140 GHz) bands, and we have detected several flares of Sgr A*. We found intraday variation of Sgr A* in the 2000 March flare. The twofold increase timescale is estimated to be about 1.5 hr at 140 GHz. This intraday variability suggests that the physical size of the flare-emitting region is compact on a scale at or below about 12 AU (~150 Rs; Schwarzschild radius). On the other hand, clear evidence of long-term periodic variability was not found from a periodicity analysis of our current millimeter data set. \\ ( http://arXiv.org/abs/astro-ph/0512625 , 861kb) -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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Guest_Richard Trigaux_* |
Dec 30 2005, 05:45 PM
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#13
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Guests |
QUOTE (ljk4-1 @ Dec 30 2005, 05:33 PM) This intraday variability suggests that the physical size of the flare-emitting region is compact on a scale at or below about 12 AU (~150 Rs; Schwarzschild radius). That makes about 20 million kilometres in diametre for the black hole (the Schwarzchild sphere). The size of a giant star. Expectably such a thing is able to swallow a Sun-sized star without letting any matter escape, only large stars could let some matter out. But even in the case of a small star like the Sun, it would be elongated by the tides, and become much more luminous and voluminous just before disappearing. Perhaps even in this case there could be some ejection of matter. Not accounting with the case where even a minor star comes just grazing the surface of the Schwarzchild sphere; in this case there could be strong ejections of hot matter, coming after to form an accretion disk and a long time of increased activity. But the minor activity observed is likely only the activity of a smaller accretion disk gathering clouds of gas and dust. |
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Jan 4 2006, 03:07 AM
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#14
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
Paper: astro-ph/0512657
Date: Fri, 30 Dec 2005 20:55:34 GMT (102kb) Title: EXIST: All-Sky Hard X-ray Imaging and Spectral-Temporal Survey for Black Holes Authors: Jonathan E. Grindlay (and the EXIST Team) Comments: 4 pages, 1 figure. Presented at LBL Surveys Workshop Journal-ref: New Astronomy Reviews, Volume 49, iss. 7-9, pp. 436-439 (2005) \\ The Energetic X-ray Imaging Survey Telescope (EXIST) is under study for the proposed Black Hole Finder Probe, one of the three Einstein Probe missions in NASA's proposed Beyond Einstein Program. EXIST would have unique capabilities: it would survey the full sky at 5-600 keV each 95min orbit with 0.9-5 arcmin, 10microsec - 45min, and ~0.5-5 keV resolution to locate sources to 10arcsec and enable black holes to be surveyed and studied on all scales. With 5sigma survey sensitivity (0.5-1y) Fx(40-80 keV) ~5 x 10^-13 cgs, or comparable to the ROSAT soft X-ray (0.3-2.5 keV) sky survey, a large sample (~2-4 x 10^4) of obscured AGN will be identified and a complete sample of accreting stellar mass BHs in the Galaxy will be found. The all-sky/all-time coverage will allow rare events to be measured, such as possible stellar disruption flares from dormant AGN out to ~200 Mpc. A large sample (~2-3/day) of GRBs will be located (<~10arcsec) at sensitivities and bandwidths much greater than previously and likely yield the highest redshift events and constraints on Pop III BHs. An outline of the mission design from the ongoing concept study is presented. \\ ( http://arXiv.org/abs/astro-ph/0512657 , 102kb) Paper: astro-ph/0512642 Date: Thu, 29 Dec 2005 20:32:57 GMT (239kb) Title: Massive Black Hole Binaries from Collisional Runaways Authors: M. Atakan G\"urkan, John M. Fregeau and Frederic A. Rasio (Northwestern University) Comments: 4 pages with emulateapj. Submitted to ApJ Letters \\ Recent theoretical work has solidified the viability of the collisional runaway scenario in young dense star clusters for the formation of very massive stars (VMSs), which may be precursors to intermediate-mass black holes (IMBHs). We present first results from a numerical study of the collisional runaway process in dense star clusters containing primordial binaries. Stellar collisions during binary scattering encounters offer an alternate channel for runaway growth, somewhat independent of direct collisions between single stars. We find that clusters with binary fractions >~10% yield two VMSs via collisional runaways, presenting the exotic possibility of forming IMBH--IMBH binaries in star clusters. We discuss the implications for gravitational wave observations, and the impact on cluster structure. \\ ( http://arXiv.org/abs/astro-ph/0512642 , 239kb) ------------------------------------------------------------------------------ \\ Paper: astro-ph/0512643 Date: Thu, 29 Dec 2005 21:40:40 GMT (223kb) Title: G359.95-0.04: Pulsar Candidate Near Sgr A* Authors: Q. D. Wang (UMass/IAS), F. J. Lu (UMass/IHEP), and E. V. Gotthelf (Columbia U.) Comments: 11 pages, accepted for publication in MNRAS, higher resolution version at http://www.astro.umass.edu/~wqd/papers/xcomet.pdf \\ We report the discovery of a prominent nonthermal X-ray feature located near the Galactic center that we identify as an energetic pulsar wind nebula. This feature, G359.95-0.04, lies 1 lyr north of Sgr A* (in projection), is comet-like in shape, and has a power law spectrum that steepens with increasing distance from the putative pulsar. The distinct spectral and spatial X-ray characteristics of the feature are similar to those belonging the rare class of ram-pressure confined pulsar wind nebulae. The luminosity of the nebula at the distance of \sgra, consistent with the inferred X-ray absorptions, is 1 10^{34} ergs s^{-1} in the 2--10 keV energy band. The cometary tail extends back to a region centered at the massive stellar complex IRS 13 and surrounded by enhanced diffuse X-ray emission, which may represent an associated supernova remnant. Furthermore, the inverse Compton scattering of the strong ambient radiation by the nebula consistently explains the observed TeV emission from the Galactic center. We also briefly discuss plausible connections of G359.95-0.04 to other high-energy sources in the region, such as the young stellar complex IRS 13 and SNR Sgr A East. \\ ( http://arXiv.org/abs/astro-ph/0512643 , 223kb) -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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Jan 5 2006, 06:31 PM
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#15
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
A DYING STAR REVEALS MORE EVIDENCE FOR A NEW KIND OF BLACK HOLE
Scientists using NASA's Rossi X-ray Timing Explorer have found a doomed star orbiting what appears to be a medium-sized black hole – a theorized "in-between" category of black hole that has eluded confirmation and frustrated scientists for more than a decade. With the discovery of the star and its orbital period, scientists are now one step away from measuring the mass of such a black hole, a step which would help verify its existence. The star's period and location already fit into the main theory of how these black holes could form. A team led by Prof. Philip Kaaret of the University of Iowa, Iowa City, announced these results today in Science Express. The results will also appear in the Jan. 27 issue of Science. "We caught this otherwise ordinary star in a unique stage in its evolution, toward the end of its life when it has bloated into a red giant phase," said Kaaret. "As a result, gas from the star is spilling into the black hole, causing the whole region to light up. This is a well-studied region of the sky, and we spotted the star with a little luck and a lot of perseverance." http://www.nasa.gov/centers/goddard/news/t..._blackhole.html -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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Jan 9 2006, 04:03 PM
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#16
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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 |
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Guest_Richard Trigaux_* |
Jan 9 2006, 06:29 PM
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#17
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Guests |
So that we shall be able to HEAR the black holes ringing when forming!!!
If black holes are related to gamma ray bursts, they may form eventually about one black hole per day in the observble universe. But, like the gamma ray bursts, they are very far. Some thinking: oscillation modes of black holes are gravitationnal waves which propagate around (or inward-out) the black hole. In order to emitt toward the outside, they must be near the horizon. Inner modes may not emitt outside the black hole. If basic black holes are about 10kms in diametre, a wave can turn around it at 10khz, or more.(this is not an exact calculus, just an order of magnitude) Giant galactic black holes could eventually oscillate at much lower frequencies, when they swallow a star, for instance 0.01hz for a 10 million kms wide black hole. Intermediary frequencies would point at intermediary sized black holes. I wait for hearing the sound, and wonder how many time a black hole may keep ringing before losing its energy. If this time is short, we shall hear like piano notes from time to time (although I don't expect that black holes harmonics are as pleasant as piano harmonics). If this time is in the order of some days, we may hear an everchanging cosmic chord, eventually nice. |
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Jan 10 2006, 03:16 PM
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#18
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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 |
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Jan 10 2006, 05:34 PM
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#19
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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 |
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Jan 11 2006, 04:36 PM
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#20
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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 |
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Jan 19 2006, 04:29 PM
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#21
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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 |
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Jan 20 2006, 04:03 PM
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#22
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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 |
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Jan 20 2006, 07:02 PM
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#23
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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 |
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Jan 31 2006, 09:27 PM
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#24
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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 |
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Feb 1 2006, 04:07 PM
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#25
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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 |
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Feb 2 2006, 10:30 PM
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#26
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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 |
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Feb 3 2006, 04:18 PM
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#27
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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 |
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Feb 6 2006, 07:43 PM
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#28
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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 |
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Feb 10 2006, 03:39 PM
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#29
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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 |
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Feb 15 2006, 02:44 PM
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#30
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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 |
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Feb 16 2006, 03:49 PM
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#31
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
Astrophysics, abstract
astro-ph/0602307 From: Rob Fender [view email] Date: Tue, 14 Feb 2006 12:08:04 GMT (61kb) A transient relativistic radio jet from Cygnus X-1 Authors: R.P. Fender (Southampton), A.M.Stirling (Manchester), R.E. Spencer (Manchester), I. Brown (Manchester), G.G. Pooley (MRAO), T.W.B. Muxlow (Manchester), J.C.A. Miller-Jones (Amsterdam) Comments: Accepted for publication in MNRAS We report the first observation of a transient relativistic jet from the canonical black hole candidate, Cygnus X-1, obtained with the Multi-Element Radio-Linked Interferometer Network (MERLIN). The jet was observed in only one of six epochs of MERLIN imaging of the source during a phase of repeated X-ray spectral transitions in 2004 Jan--Feb, and this epoch corresponded to the softest 1.5-12 keV X-ray spectrum. With only a single epoch revealing the jet, we cannot formally constrain its velocity. Nevertheless, several lines of reasoning suggest that the jet was probably launched 0.5-4.0 days before this brightening, corresponding to projected velocities of 0.2c < v_app < 1.6c, and an intrinsic velocity of > 0.3c. We also report the occurrence of a major radio flare from Cyg X-1, reaching a flux density of ~120 mJy at 15 GHz, and yet not associated with any resolvable radio emission, despite a concerted effort with MERLIN. We discuss the resolved jet in terms of the recently proposed 'unified model' for the disc-jet coupling in black hole X-ray binaries, and tentatively identify the 'jet line' for Cyg X-1. The source is consistent with the model in the sense that a steady jet appears to persist initially when the X-ray spectrum starts softening, and that once the spectral softening is complete the core radio emission is suppressed and transient ejecta / shock observed. However, there are some anomalies, and Cyg X-1 clearly does not behave like a normal black hole transient in progressing to the canonical soft / thermal state once the ejection event has happened. http://arxiv.org/abs/astro-ph/0602307 -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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