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Astronomy/new Discoveries, Deep space, galactic & extragalactic |
 Jan 30 2006, 07:04 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  |
QUOTE (ljk4-1 @ Jan 27 2006, 09:49 PM) SURPRISE! MOST STARS ARE SINGLE Astronomers have known since the 1700s that a significant fraction of stars belong to binary or multiple systems. But what is that fraction? Given the observed fact that most solar-size and larger stars reside in binaries, many astronomers have concluded that more than half of our galaxy's stars belong to multiple-star systems. But a new study shows that the conventional wisdom is almost certainly wrong. The problem is that astronomers have neglected to consider our galaxy's most common stellar denizens: red dwarfs. These low-mass, low-luminosity stars make up more than 80 percent of all the stars in the Milky Way.... http://SkyandTelescope.com/news/article_1669_1.asp  Astrophysics, abstract astro-ph/0601375 From: Charles J. Lada [view email] Date: Tue, 17 Jan 2006 20:56:12 GMT (44kb) Stellar Multiplicity and the IMF: Most Stars Are Single Born Authors: Charles J. Lada Comments: Submitted to Astrophysical Journal Letters, 5 pages, 2 figures. Complete paper can be also obtained at this http URL: http://www.cfa.harvard.edu/~clada/pubs_html/binaries.html In this short communication I compare recent findings suggesting a low binary star fraction for late type stars with knowledge concerning the forms of the stellar initial and present day mass functions for masses down to the hydrogen burning limit. This comparison indicates that most stellar systems formed in the galaxy are likely single and not binary as has been often asserted. Indeed, in the current epoch two-thirds of all main sequence stellar systems in the Galactic disk are composed of single stars. Some implications of this realization for understanding the star and planet formation process are briefly mentioned. http://arxiv.org/abs/astro-ph/0601375 -------------------- "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, 10:36 PM
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#17
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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/9306035 From: Andrei Linde [view email] Date: Tue, 29 Jun 1993 05:15:07 GMT (609kb) Date (revised): Wed, 1 Feb 2006 20:20:32 GMT Date (revised): Wed, 1 Feb 2006 21:03:31 GMT From the Big Bang Theory to the Theory of a Stationary Universe Authors: Andrei Linde, Dmitri Linde, Arthur Mezhlumian Comments: No changes to the file, but original figures are included. They substantially help to understand this paper, as well as eternal inflation in general, and what is now called the "multiverse" and the "string theory landscape." High quality figures can be found at this http URL Journal-ref: Phys.Rev. D49 (1994) 1783-1826 We consider chaotic inflation in the theories with the effective potentials phi^n and e^{\alpha\phi}. In such theories inflationary domains containing sufficiently large and homogeneous scalar field \phi permanently produce new inflationary domains of a similar type. We show that under certain conditions this process of the self-reproduction of the Universe can be described by a stationary distribution of probability, which means that the fraction of the physical volume of the Universe in a state with given properties (with given values of fields, with a given density of matter, etc.) does not depend on time, both at the stage of inflation and after it. This represents a strong deviation of inflationary cosmology from the standard Big Bang paradigm. We compare our approach with other approaches to quantum cosmology, and illustrate some of the general conclusions mentioned above with the results of a computer simulation of stochastic processes in the inflationary Universe. http://arxiv.org/abs/gr-qc/9306035 -------------------- "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, 07:55 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 |
Milky Way's fastest pulsar is on its way out of the galaxy, astronomers find
http://www.news.cornell.edu/stories/Feb06/....pulsar.lg.html Feb. 6, 2006 By Dave Finley and Lauren Gold lg34@cornell.edu The Milky Way's fastest observed pulsar is speeding out of the galaxy at more than 670 miles a second, propelled largely by a kick it received at its birth 2.5 million years ago. Using the Very Long Baseline Array (VLBA), 10 radio telescopes spanning 5,000 miles from Hawaii to the U.S. Virgin Islands, James Cordes, professor of astronomy at Cornell University, his former student Shami Chatterjee, now of the Harvard-Smithsonian Center for Astrophysics, and colleagues studied the pulsar (a fast-spinning neutron star) B1508+55, about 7,700 light years from Earth. With the ultra-sharp radio vision of the continentwide VLBA, they precisely measured both the distance and the speed of the pulsar. The team then plotted the star's motion backward to a birthplace among groups of giant stars in the constellation Cygnus, which contains stars so massive they inevitably explode as supernovae. Commenting on the research, which was published last fall in Astrophysical Journal Letters, Chatterjee said, "We know that supernova explosions can give a kick to the resulting neutron star, but the tremendous speed of this object pushes the limits of our current understanding. This discovery is very difficult for the latest models to explain." Chatterjee is also a Jansky fellow at the National Radio Astronomy Observatory (NRAO). The VLBA measurements show the pulsar moving at nearly 1,100 kilometers (more than 670 miles) per second. At this speed, it could travel from London to New York in five seconds. -------------------- "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 7 2006, 06:35 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 |
Astrophysics, abstract
astro-ph/0602101 From: John F. Beacom [view email] Date: Sun, 5 Feb 2006 21:21:31 GMT (51kb) The Cosmic Stellar Birth and Death Rates Authors: John F. Beacom (Ohio State University) Comments: Accepted for publication in New Astronomy Reviews (invited talk at "Astronomy with Radioactivities V", Clemson Univ., Sept. 2005). 9 pages, 5 figures The cosmic stellar birth rate can be measured by standard astronomical techniques. It can also be probed via the cosmic stellar death rate, though until recently, this was much less precise. However, recent results based on measured supernova rates, and importantly, also on the attendant diffuse fluxes of neutrinos and gamma rays, have become competitive, and a concordant history of stellar birth and death is emerging. The neutrino flux from all past core-collapse supernovae, while faint, is realistically within reach of detection in Super-Kamiokande, and a useful limit has already been set. I will discuss predictions for this flux, the prospects for neutrino detection, the implications for understanding core-collapse supernovae, and a new limit on the contribution of type-Ia supernovae to the diffuse gamma-ray background. http://arxiv.org/abs/astro-ph/0602101 -------------------- "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 7 2006, 06:50 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 |
Astrophysics, abstract
astro-ph/0602117 From: T. Padmanabhan [view email] Date: Mon, 6 Feb 2006 13:49:38 GMT (909kb) Advanced Topics in Cosmology: A Pedagogical Introduction Authors: T. Padmanabhan Comments: 40 pages; 6 figures; RevTex4; Extended version of Lecture Courses given at several places including X Special Courses at Observatorio Nacional, Rio de Janeiro, Brazil during 26-30 Sept, 2005. To appear in the Proceedings These lecture notes provide a concise, rapid and pedagogical introduction to several advanced topics in contemporary cosmology. The discussion of thermal history of the universe, linear perturbation theory, theory of CMBR temperature anisotropies and the inflationary generation of perturbation are presented in a manner accessible to someone who has done a first course in cosmology. The discussion of dark energy is more research oriented and reflects the personal bias of the author. Contents: (I) The cosmological paradigm and Friedmann model (II) Thermal history of the universe (III) Structure formation and linear perturbation theories (IV) Perturbations in dark matter and radiation (V) Transfer function for matter perturbations (VI) Temperature anisotropies of CMBR (VII) Generation of initial perturbations from inflation (VIII) The dark energy. http://arxiv.org/abs/astro-ph/0602117 -------------------- "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 7 2006, 06:54 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 |
Astrophysics, abstract
astro-ph/0602122 From: Adam J. Burgasser [view email] Date: Mon, 6 Feb 2006 15:58:28 GMT (155kb) Not Alone: Tracing the Origins of Very Low Mass Stars and Brown Dwarfs Through Multiplicity Studies Authors: Adam J. Burgasser (MIT), I. Neill Reid (STScI), Nick Siegler (UA Steward), Laird Close (UA Steward), Peter Allen (Penn State), Patrick Lowrance (SSC), John Gizis (U Delaware) Comments: 16 pages, 7 figures, contributed chapter for Planets and Protostars V meeting (October 2005); full table of VLM binaries can be obtained at this http URL The properties of multiple stellar systems have long provided important empirical constraints for star formation theories, enabling (along with several other lines of evidence) a concrete, qualitative picture of the birth and early evolution of normal stars. At very low masses (VLM; M <~ 0.1 M_sun), down to and below the hydrogen burning minimum mass, our understanding of formation processes is not as clear, with several competing theories now under consideration. One means of testing these theories is through the empirical characterization of VLM multiple systems. Here, we review the results of various VLM multiplicity studies to date. These systems can be generally characterized as closely separated (93% have projected separations Delta < 20 AU) and near equal-mass (77% have M_2/M_1 >= 0.8) occurring infrequently (perhaps 10-30%). Both the frequency and maximum separation of stellar and brown dwarf binaries steadily decrease for lower system masses, suggesting that VLM binary formation and/or evolution may be a mass-dependent process. There is evidence for a fairly rapid decline in the number of loosely-bound systems below ~0.3 M_sun, corresponding to a factor of 10-20 increase in the minimum binding energy of VLM binaries as compared to more massive stellar binaries. This wide-separation ``desert'' is present among both field (~1-5 Gyr) and older (> 100 Myr) cluster systems, while the youngest (<~10 Myr) VLM binaries, particularly those in nearby, low-density star forming regions, appear to have somewhat different systemic properties. We compare these empirical trends to predictions laid out by current formation theories, and outline future observational studies needed to probe the full parameter space of the lowest mass multiple systems. http://arxiv.org/abs/astro-ph/0602122 -------------------- "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 14 2006, 02:41 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 |
Supernova in Spiral Galaxy Messier 100
Discovered is shared by Shoji Suzuki (Japan) and M. Migliardi of CROSS (Italy). A type Ia supernova found 1-2 weeks before maximum light. M100 is one of our more prolific galaxies when it comes to supernovae. This will be the fifth one observed in the 100+ years we have been looking. The last one was 1979C. We have a DSS Photometry reference image made by Odd Trondal. Icon generated from the CROSS color image. This supernova is in the Constellation Coma Berenices. http://www.rochesterastronomy.org/sn2006/sn2006X.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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Feb 16 2006, 12:52 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 |
SUCKED IN! OUR GALAXY EATS NEIGHBOUR (Space & Astronomy News, 14/2/06)
Astronomers have released new evidence to show that a region of stars in our galaxy known as the Arcturus stream is the digested remains of what was once a neighbouring galaxy. http://www.abc.net.au/science/news/space/S...ish_1568599.htm -------------------- "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, 02:25 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 |
STELLAR CHEMISTRY
- Rogue Pulsar Speeding Out Of The Galaxy http://www.spacedaily.com/reports/Rogue_Pu...The_Galaxy.html Charlottesville VA (SPX) Feb 15, 2006 - Astronomers have precisely calculated the speed of the Milky Way's fastest observed pulsar: It is heading out of the galaxy at more than 670 miles a second, propelled by an explosive kick it received at birth some 2.5 million years ago. - VLT Unveils Metal-Rich Distant Galaxy http://www.spacedaily.com/reports/VLT_Unve...ant_Galaxy.html - Astronomers Discover 'RRATS' In The Cosmos http://www.spacedaily.com/reports/Astronom...The_Cosmos.html - Galactic Center Found To Glow Unevenly http://www.spacedaily.com/reports/Galactic...w_Unevenly.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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Feb 16 2006, 06:48 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 |
QUOTE (ljk4-1 @ Feb 16 2006, 09:25 AM) - Astronomers Discover 'RRATS' In The Cosmos http://www.spacedaily.com/reports/Astronom...The_Cosmos.html Astronomers Discover Peek-A-Boo Stars http://www.space.com/scienceastronomy/060215_new_stars.html A newfound type of rotating stars played peek-a-boo with astronomers, appearing and disappearing a few times each day. -------------------- "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 23 2006, 07:45 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 |
QUOTE (ljk4-1 @ Feb 14 2006, 09:41 AM) Supernova in Spiral Galaxy Messier 100 Discovered is shared by Shoji Suzuki (Japan) and M. Migliardi of CROSS (Italy). A type Ia supernova found 1-2 weeks before maximum light. M100 is one of our more prolific galaxies when it comes to supernovae. This will be the fifth one observed in the 100+ years we have been looking. The last one was 1979C. We have a DSS Photometry reference image made by Odd Trondal. Icon generated from the CROSS color image. This supernova is in the Constellation Coma Berenices. http://www.rochesterastronomy.org/sn2006/sn2006X.html Supernova in Grand Design Spiral Galaxy http://www.spaceref.com/news/viewpr.html?pid=19101 "Possibly similar to what our own Milky Way looks like, Messier 100 is a grand design spiral galaxy that presents an intricate structure, with a bright core and two prominent arms, showing numerous young and hot massive stars as well as extremely hot knots (HII regions). Two smaller arms are also seen starting from the inner part and reaching towards the larger spiral arms." -------------------- "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 24 2006, 03:47 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 |
STELLAR CHEMISTRY
- Building A Better Guide To The Galaxy http://www.spacedaily.com/reports/Building...The_Galaxy.html Charlottesville VA (SPX) Feb 23, 2006 - It is the job of astronomers to put numbers on the stupefying vastness of space and the objects it holds. That's how they get the universe to spill its secrets. The University of Virginia's Steve Majewski and his team plan to use NASA's SIM PlanetQuest space telescope to make ultra-precise measurements that will reveal more about the nature of our galaxy than ever before. - ESO's VLT Launches Laser Guide Star http://www.spacedaily.com/reports/ESOs_VLT...Guide_Star.html - Swift Might Have Detected A Supernova Just Beginning http://www.spacedaily.com/reports/Swift_Mi..._Beginning.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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