Friday, January 13, 2012 3:46:13 AM
Super-fat galaxy cluster confirms existence of dark matter and dark energy
Cosmic crash. El Gordo consists of two clusters in collision, as revealed by the two separate swarms of individual galaxies (red) and the asymmetric cloud of hot, x-ray emitting gas (blue) in between.
Credit: ESO/SOAR/NASA
[ http://news.sciencemag.org/sciencenow/2012/01/when-galaxies-crash.html ]
By Alasdair Wilkins
Jan 10, 2012 11:44 AM
This galaxy cluster is nicknamed El Gordo, which means "The Fat One" in Spanish. Located seven billion light-years away, it's the biggest cluster ever found at that distance — and it's resounding proof that dark matter is everywhere in the cosmos.
The cluster is the result of two smaller clusters colliding into each other at several million miles per hour. It appears that this collision is actually pulling normal matter away from its dark counterpart, as the galaxy's hot gas has been slowed down by the collision while the dark matter keeps moving at the same speed.
Rutgers astronomer Felipe Menanteau, who led the study of this cluster, dramatically describes El Gordo as "the most massive, the hottest, and gives off the most X-rays of any cluster found so far at this distance or beyond." As the largest structures in the universe held together by gravity, galaxy clusters are an effective tool for studying the presence of dark matter and dark energy throughout the universe. Clusters will form in different ways depending on the amounts of these mysterious phenomena [which] are present at that particular point in space and time.
It's extremely rare to find a cluster as massive as El Gordo this early in the universe's life — it comes from a time when the universe was about half its present age — but everything about it completely checks out with what astronomers would expect to find based on the current model, which holds that the universe began with the Big Bang and is largely made up of dark matter and dark energy.
Via ESO [ http://www.eso.org/public/news/eso1203/ ].
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Copyright 2012 io9.com
http://io9.com/5874880/super+fat-galaxy-cluster-confirms-existence-of-dark-matter-and-dark-energy [with comments]
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Monster Galaxy Cluster 'El Gordo' Packs Mass of 2 Quadrillion Suns
10 January 2012
http://www.space.com/14192-largest-galaxy-cluster-el-gordo-photo-aas219.html [with comments] [also at http://www.csmonitor.com/Science/2012/0111/Humongous-El-Gordo-galaxy-cluster-packs-mass-of-2-quadrillion-stars (no comments yet)]
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Hubble Survey Finds Galaxies Far, Far Away
Hubble Pinpoints Farthest Protocluster of Galaxies Ever Seen
January 10, 2012: NASA's Hubble Space Telescope has uncovered a cluster of galaxies in the initial stages of construction — the most distant such grouping ever observed in the early universe.
In a random sky survey made in near-infrared light, Hubble spied five tiny galaxies clustered together 13.1 billion light-years away. They are among the brightest galaxies at that epoch and very young, existing just 600 million years after the universe's birth in the big bang.
[ http://hubblesite.org/newscenter/archive/releases/2012/05/image/a/format/web_print/ ; http://hubblesite.org/newscenter/archive/releases/2012/05/ ]
Posted by Jason Major
January 10, 2012
The image above, a composite of visible and infrared light images captured by the Hubble Space Telescope, shows the newfound locations of five small and incredibly ancient galaxies which are in the process of merging into a galactic cluster.
Located a staggering 13.1 billion light-years away, these galaxies were in existence a mere 600 million years after the Big Bang!
This collection of infant galaxies is now the furthest — and thus oldest — known protocluster in the Universe.
Galactic clusters are particularly significant as they are the largest structures in the Universe. (Our own Milky Way is part of a cluster known as the Local Group, which contains about 45 separate galaxies.)
The distant galaxies were discovered during a random sky survey. A team led by Michele Trenti of the University of Colorado at Boulder and the Institute of Astronomy at the University of Cambridge in the UK used Hubble’s Wide Field Camera 3 (WFC3) to scan the sky in near-infrared, looking for distant sources of bright energy.
Such ancient galaxies cannot be seen in visible wavelengths, as their light has been stretched into the infrared portion of the spectrum by their ever-increasing distance.
“We need to look in many different areas because the odds of finding something this rare are very small,” said Trenti, “Typically, a region has nothing, but if we hit the right spot, we can find multiple galaxies.”
This news was announced today at the American Astronomical Society meeting in Austin, Texas. Read the official NASA release here [ http://hubblesite.org/newscenter/archive/releases/2012/05/text/ ].
Credit: NASA, ESA, M. Trenti (University of Colorado, Boulder, and Institute of Astronomy, University of Cambridge, UK), L. Bradley (STScI), and the BoRG team
© 2012 National Geographic Society
http://newswatch.nationalgeographic.com/2012/01/10/hubble-survey-finds-galaxies-far-far-away/ [with comments]
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Our Milky Way Galaxy Is as White as, Well, Milk
January 12, 2012
http://newswatch.nationalgeographic.com/2012/01/12/our-milky-way-galaxy-is-as-white-as-well-milk/ [no comments yet]
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Milky Way Galaxy's Past Revealed Through New Star Census
Measurements of the metal content of stars in the Milky Way's disk, using stars observed by the SEGUE-2 survey. The bottom panel shows the decrease in metal content as the distance from the galactic center increases for stars near the plane of the Milky Way disk. The metal content for stars far above the plane, shown in the upper panel, is nearly constant at all distances from the galactic center.
CREDIT: Judy Cheng and Connie Rockosi (University of California, Santa Cruz); 2MASS Survey
by Clara Moskowitz, SPACE.com Assistant Managing Editor
Date: 10 January 2012 Time: 10:14 AM ET
AUSTIN, Texas — Scientists are performing a census of the stars in the Milky Way in an effort to piece together the history of how our galaxy formed.
Researchers working on the Sloan Extension for Galactic Understanding and Exploration 2 (SEGUE-2) project, part of the Sloan Digital Sky Survey III [ http://www.space.com/10613-largest-color-sky-image-map-created-110111.html ], have now observed more than 118,000 ancient stars that were born back when our galaxy was a fraction of its present age.
"By studying these stars, we can learn what our galaxy was like when it was young, and how it grew and evolved," said Constance Rockosi, University of California, Santa Cruz astronomer and principal investigator of the SEGUE-2 project, during a presentation here on Monday (Jan. 9) at the 219th meeting of the American Astronomical Society.
For each of the 118,000 stars observed, the researchers measured positions, motions and chemical compositions. [Top 10 Star Mysteries [ http://www.space.com/24-top-10-star-mysteries.html ]]
"We put those together to try to tell the story of how the galaxy was born, and how it grew to be the way it is today," Rockosi said.
Building up metals
When the Milky Way's first stars [ http://www.space.com/12740-milky-baby-stars-growth-spurt.html ] formed, they condensed out of clouds of hydrogen and helium. Inside these stars, hydrogen and helium merged together to form the first heavy elements like carbon, nitrogen and oxygen. It was only when the most massive of these stars died in supernova explosions that some of the heavier metal elements formed [ http://www.space.com/13781-ancient-stars-galaxy-history.html ] and dispersed into surrounding space.
As subsequent generations of stars were born from this material, they contained higher concentrations of these heavy metals.
Thus, by studying stars' metal content (called metallicity), astronomers can tell how many generations of stars came before them.
The SEGUE-2 researchers used their metallicity findings to probe the history of a particular part of the Milky Way, called its disk. This is the relatively flat, pancake-shaped part of a spiral galaxy that contains its spiral arms.
Thin and thick disks
Many of the disk stars are restricted to a dense thin disk, though some stars stray above or below the plane in what's called the thick disk.
"The question we'd like to answer is, how did the thick disk form?" said Judy Cheng, University of California, Santa Cruz astronomer.
To address that question, the scientists measured how the disk stars' metallicities changed with their distances from the center of the galaxy. They found that in the thick disk, distance had no effect on metal content, but for stars in the thin disk, there was a gradient, with those in the inside of the galaxy containing more metal elements than those on the outside.
"This tells us the thin disk formed inside-out," Cheng said. The inside of the thin disk must have formed first, she explained, giving the center of the disk more time to accumulate metals from generation after generation of stars, while those in the newer, younger outside region were relatively metal-poor.
In contrast, the uniformity in metal content of the thick disk points to two possible formation scenarios for this part of our galaxy.
One possibility is that the thick disk formed all at once, leaving the metals spread evenly throughout it. Another alternative is that the thick disk used to have a metallicity gradient, but over time, and through a dynamic event such as an interaction with a smaller galaxy [ http://www.space.com/12952-milkyway-galaxy-shape-galactic-crash.html ], the stars in the thick disk got stirred up.
"It either formed rapidly or it's been mixed very well," Cheng said.
Copyright © 2012 TechMediaNetwork.com
http://www.space.com/14187-milky-disk-stars-galaxy-formation-segue.html [with comments]
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Missing companion star indicates a Type Ia supernova came from merging dwarfs
Photograph by heritage.stsci.edu
("Finding the star in this supernova could unlock the secrets of the universe",
http://io9.com/5875677/finding-the-star-in-this-supernova-could-unlock-the-secrets-of-the-universe )
By Matthew Francis | Published January 12, 2012
Type Ia supernovae are some of the brightest explosions in the Universe, and some of the most important, since they help us measure the Universe's expansion. Nevertheless, determining exactly what is going on to produce this type of supernova has been a challenge: though white dwarfs are almost certainly involved, astronomers have yet to identify the exact process that causes one to explode. Recent analysis of Hubble Space Telescope data, performed by Bradley E. Schaefer and Ashley Pagnotta of Louisiana State University, argues strongly that at least some type Ia supernovae are the result of a merger between two white dwarfs.
A white dwarf is the dense core that remains after a relatively low-mass star like our Sun has burned through its lighter elements. The heat of fusion is no longer able to counteract a gravity-driven collapse; instead, it's balanced by quantum degeneracy pressure from the Pauli exclusion principle. If it collapsed any further, electrons would be forced into the same quantum state, which isn't possible. (This is similar to the force that keeps neutron stars [ http://arstechnica.com/science/news/2012/01/some-neutron-stars-might-shed-their-skins.ars ] from collapsing.)
There is a limit to how massive a white dwarf can be: the Chandrasekhar limit, which is about 1.4 times the mass of the Sun. If a white dwarf's mass reaches that limit, it is no longer stable. According to a widely accepted model, it then explodes as a type Ia supernova. Because white dwarfs all have similar characteristics and the same mass when they explode, their explosions should be similar. As a result, they are considered "standard candles," objects with a known intrinsic brightness. That brightness provides an independent measure of their distance, and acts as the foundation for much of modern observational cosmology, including the research behind the 2011 Nobel Prize [ http://arstechnica.com/science/news/2011/10/physics-nobel-goes-to-the-dark-side-of-the-universe.ars ] in physics.
Despite their fundamental importance to cosmology and astrophysics, how type Ia supernovae are produced is still unclear. Several significant models have been proposed, two of which are important for the current work. The double-degenerate model predicts two white dwarfs (degenerate objects) in a close binary; over time, their mutual orbit would decay through gravitational radiation until they collided.
In the single-degenerate model, a white dwarf is in a binary system with an ordinary star. The white dwarf strips gas from its companion's envelope until it has gathered enough to reach the Chandrasekhar limit, after which it explodes.
Stars are difficult to destroy; even an explosion as energetic as a type Ia supernova won't completely annihilate a companion star in a single-degenerate explosion, according to astronomers' best understanding. As Carles Badenes, a supernova researcher at the University of Pittsburgh explains, "We know the white dwarf is obliterated, but the companion star must survive, so it will still be present in the supernova remnant." But a double-degenerate type Ia supernova, since it involves an actual collision, would destroy both white dwarfs, leaving nothing but gas behind in the region where the binary once existed.
Schaefer and Pagnotta carefully analyzed the type Ia supernova remnant SNR 0509-67.5 in the Large Magellanic Cloud. It's the leftovers of an explosion that would have first been visible from Earth about 400 years ago. Any companion star that survived the blast must lie within a certain radius of the supernova's heart, or it wouldn't have been close enough to have gas pulled off by the white dwarf's gravity. The researchers carefully analyzed that region for sufficiently bright stars and star cores.
They found no candidates for a companion star brighter than an absolute magnitude of +8.4 (apparent magnitude +26.9 at that distance)—if there is a companion object, it is very faint. The nearby stars that are bright enough are too far outside the center of the supernova remnant to have fed gas into the white dwarf, the researchers concluded with a confidence of 99.7 percent. Badenes points out if this was a single-degenerate system, "That places very strong limits on the mass range of the star in the original binary system," itself an interesting result.
If the companion star is completely absent, a result consistent with the data, then maybe the double-degenerate model explains the origin of SNR 0509-67.5. In fact, no companion star has ever been identified in a type Ia supernova remnant, with the possible exception of Tycho's supernova—one's been claimed there, but its identity is disputed by many researchers. Proof of a negative is difficult, however: at best, the single case of SNR 0509-67.5 shows that the single-degenerate model doesn't apply to that event. Schaefer and Pagnotta argue that only a double-degenerate binary could be responsible for the supernova.
"Whether or not you agree with the strong conclusions [of the authors]," says Badenes, "this result is very interesting." Perhaps other type Ia supernovae are single-degenerate, but the missing massive companion star predicted by the single-degenerate model in SNR 0509-67.5 is at least consistent with a double-degenerate system. Follow-up observations of this and other type Ia supernova remnants will bring astronomers closer to an understanding of what actually causes these important explosions.
Nature, 2012 [ http://www.nature.com/nature/journal/v481/n7380/full/nature10692.html ]. DOI: 10.1038/nature10692 [ http://dx.doi.org/10.1038/nature10692 ].
Ars Technica © 2012 Condé Nast Digital
http://arstechnica.com/science/news/2012/01/the-companion-star-that-wasnt-there.ars [with comments]
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Mystery of 400-Year-Old Star Explosion Finally Solved
11 January 2012
http://www.space.com/14202-supernova-explosion-mystery-solved-aas219.html [with comments]
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Astrophysics: Progenitors of type Ia supernovae
Pilar Ruiz-Lapuente1
Published online11 January 2012
A study of the remains of a type Ia supernova whose light swept past Earth about 400 years ago finds no sign of a companion star. The result indicates that the supernova's progenitor was a pair of white dwarfs.
http://www.nature.com/nature/journal/v481/n7380/full/481149a.html
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Earliest-yet observation of August supernova nails it: Destroyed star was white dwarf
Fluke observation 4 hours after star exploded allows stronger limits on size of progenitor
Public release date: 11-Jan-2012
Last year's discovery of the nearest Type Ia supernova in decades – captured only 11 hours after it exploded – allowed astronomers to finally cinch the identity of the stars behind these explosions, which have become key measures of cosmic distance.
That supernova, called SN2011fe, and presumably most Type Ia supernovae were originally white dwarfs extremely dense and compact stars composed mostly of carbon and oxygen.
Now, thanks to a much earlier, fluke observation of SN2011fe by a small robotic telescope on the island of Mallorca, University of California, Berkeley, and Lawrence Berkeley National Laboratory (LBNL) astronomers can boost confidence even higher that Type Ia supernovae originate from white dwarfs.
"A fortuitous observation only four hours after we think the star exploded allowed us to put much more constraining limits on the size of the thing that blew up," said Joshua Bloom, UC Berkeley associate professor of astronomy and first author of a paper interpreting the observation that will appear in the Jan. 10 issue of the Astrophysical Journal Letters. "The size of the progenitor is so small and the density so high, it pretty much rules out any other reasonable or even fringe possibility. This is a direct confirmation that what blew up is a carbon-oxygen white dwarf."
In 1998, two research teams used Type Ia supernovae as standard candles to conclude that the expansion of the universe is accelerating, presumably fueled by a mysterious dark energy. That discovery earned three astrophysicists, including UC Berkeley and LBNL's Saul Perlmutter, the 2011 Nobel Prize in Physics.
Bloom will present his results on Wednesday, Jan. 11, during an 11:30 a.m. CST media briefing at the national meeting of the American Astronomical Society in Austin, Texas.
Smaller than a main sequence star
Bloom and his colleagues were coauthors of two papers published Dec. 15, 2011, in the journal Nature that concluded that SN2011fe's progenitor star was a compact object with a diameter less than one-tenth that of the sun. Based on the brightness of the explosion, which occurred 21 million light years away in the Pinwheel Galaxy (M101), and the fact that the explosive debris contained large amounts of carbon and oxygen, coauthor Peter Nugent of LBNL and his colleagues concluded that before it exploded, the star was almost certainly a carbon-oxygen white dwarf.
UC Berkeley astronomer Weidong Li and colleagues concluded the same thing based on the inability of the Hubble Space Telescope to detect any star at that spot before the supernova ignited.
White dwarfs are very dense stars about the size of the Earth that burned all their hydrogen and helium into carbon and oxygen before stopping fusion altogether, destined to cool slowly into dark cinders.
After the papers were submitted to Nature in early November, UC Berkeley and LBNL astronomers learned that the 17-inch PIRATE telescope on Mallorca, operated as a remote-controlled teaching telescope by The Open University in the U.K., had obtained a deep, wide-field image of the Pinwheel Galaxy (M101) only four hours after the explosion. Because the supernova was not visible in the PIRATE image, Bloom and his colleagues, including Nugent, were able to put an even more stringent upper limit on the early brightness of the supernova.
The new analysis concludes that the progenitor star had a diameter less than one-fiftieth that of the sun – 5 to 10 times smaller than last year's limit – which implies a density 100 to 1,000 times higher.
While the previous limits ruled out hydrogen-burning main sequence stars and red giants – the most likely alternatives to a white dwarf, said Ken J. Shen, an Einstein postdoctoral fellow at LBNL and UC Berkeley – they only "placed weak constraints on smaller stars that burn helium or carbon in their cores. Only with this new observation can we now rule these out."
Looking for light from the early shock wave
UC Berkeley's Daniel Kasen, an assistant professor of physics, and Shen used theoretical models of exploding stars to estimate how bright a star of a given size would be within hours of ignition from the glow of the supernova's expanding shock wave. The bigger the star, the brighter the glow from the shock. The non-detection of the supernova four hours after it exploded enabled Kasen, Shen, Bloom and their colleagues to rule out stars larger than a white dwarf.
"This is the first time we can really be confident about what is exploding," Shen said.
Their analysis relied on theories of how a carbon-oxygen white dwarf explodes. Presumably, the white dwarf acquires mass from its binary companion until the temperature and pressure in the core rises high enough to restart fusion reactions. This time, carbon and oxygen are fused into nickel and iron in a reaction that consumes the star within seconds, blowing it up like a runaway thermonuclear bomb, Kasen said.
The first light from the explosion should be from the glow of superheated gas as the debris from the star plows through surrounding gas and dust. No one has ever caught this shockwave glow from a Type Ia supernova because it's quite dim and drops off quickly, Kasen said. The light astronomers see is from the decay of radioactive elements created in the explosion, which can shine brightly for weeks afterward.
The inability to see SN2011fe four hours after the explosion, Kasen said, allowed the team to set much more stringent limits on the size of the progenitor star.
"The earlier you get on it (the supernova), or the nearer it is, the better your chance of actually seeing the glowing outflow from the shockwave," he said. "This is the closest we've gotten. If it had been 10 instead of 20 million light years from Earth, we might have seen something four hours after the explosion."
The PIRATE observation also narrowed the limits on the companion star published last month by Li and his colleagues. The diameter of the supernova's companion must be less than one-tenth that of the sun, ruling out red giant and normal main-sequence stars.
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Other coauthors of the ApJ Letters paper are Nathaniel R. Butler of Arizona State University; Melissa L. Graham and D. Andrew Howell of UC Santa Barbara; Ulrich Kolb, Stefan Holmes and Carole Haswell of The Open University in Milton Keynes, U.K.; Vadim Burwitz of the Max Planck Institute for Extraterrestrial Physics in Germany; Juan Rodriguez of the Astronomical Observatory of Mallorca in Spain; and Mark Sullivan of the University of Oxford.
Bloom, Nugent and others are presenting new findings during a special meeting on SN 2011fe at the AAS meeting in Austin, Texas, scheduled for 9:30 a.m. Monday, Jan. 9.
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Contact: Robert Sanders
rsanders@berkeley.edu
510-643-6998
University of California - Berkeley
Copyright ©2012 by AAAS, the science society
http://www.eurekalert.org/pub_releases/2012-01/uoc--eoo010912.php
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Ancient Star Explosion is Most Distant of Its Kind
Three images from the Hubble Space Telescope reveal the birth of a Type 1a supernova, a “standard candle” for measuring the expansion of the universe. Nicknamed SN Primo, this supernova is the most distant of its type ever discovered.
CREDIT: NASA, ESA, A. Riess (Space Telescope Science Institute and The Johns Hopkins University), and S. Rodney (The Johns Hopkins University)
by Nola Taylor Redd, SPACE.com ContributorDate: 12 January 2012 Time: 12:00 PM ET
Astronomers have found the most distant Type 1a supernova, a kind of star explosion that should help scientists better understand the ever-expanding universe and the nature of dark energy, the strange force accelerating that expansion.
Bursting into existence 9 billion years ago, the supernova (nicknamed SN Primo) was born from the violent death of a shrunken, super-dense star called a white dwarf [ http://www.space.com/14202-supernova-explosion-mystery-solved-aas219.html ]. Light from such explosions falls within a very narrow range, which is why astronomers call them "standard candles." As the light travels toward Earth, astronomers can measure how it is stretched by the expansion of the universe.
The team used the Wide Field Camera 3 instrument on NASA's Hubble Space Telescope to observe the supernova in near-infrared wavelengths over eight months.
"In our search for supernovae, we had gone as far as we could go in optical light," said principal investigator Adam Riess, of the Space Telescope Science Institute and Johns Hopkins University, in a statement. "But it's only the beginning of what we can do in infrared light."
The discovery was part of a survey called the CANDELS+CLASH Supernova Project. The census searches regions targeted by two large Hubble programs, the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey and the Cluster Lensing and Supernova Survey, over the course of three years, starting in 2010. SN Primo was found in October of that same year. [Supernova Photos: Great Images of Star Explosions [ http://www.space.com/11425-photos-supernovas-star-explosions.html ]]
"This discovery demonstrates that we can use the Wide Field Camera 3 to search for supernovae in the distant universe," Riess said.
The CANDLES+CLASH team searches for ancient supernovae in an effort to understand if they’ve changed over the 13.7 billion years since the Big Bang [ http://www.space.com/13320-big-bang-universe-10-steps-explainer.html ], the dramatic event that gave birth to our universe.
"If we look into the early universe and measure a drop in the supernovae, then it could be that it takes a long time to make Type 1a supernovae," said Steve Rodney, also of Johns Hopkins.
If, on the other hand, such supernovae form quickly in the early stages of the universe, they should be plentiful.
"Every supernova is unique, so it’s possible that there are multiple ways to make a supernova," Rodney said.
If the Type 1a supernovae from the early universe look different than today’s explosions, the variations could provide more insights into dark energy.
Riess was one of three astronomers awarded the 2011 Nobel Prize in Physics [ http://www.space.com/13177-nobel-prize-accelerating-universe-dark-energy-reaction.html ] for the discovery of dark energy 13 years ago by studying Type 1a supernovae.
The findings were announced at the 219th American Astronomical Society meeting in Austin, Tex., on Wednesday (Jan 11). Rodney is lead author on a paper detailing the results that has been accepted for publication by the Astrophysical Journal.
Copyright © 2012 TechMediaNetwork.com
http://www.space.com/14221-ancient-supernova-farthest-snprimo-aas219.html [no comments yet]
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NASA'S RXTE Helps Pinpoint Launch of 'Bullets' in a Black Hole's Jet
01.10.12
Using observations from NASA's Rossi X-ray Timing Explorer (RXTE) satellite and the National Science Foundation's (NSF) Very Long Baseline Array (VLBA) radio telescope, an international team of astronomers has identified the moment when a black hole in our galaxy launched super-fast knots of gas into space.
[ http://www.youtube.com/watch?v=dF-KhAXbV8k (embedded)]
Download high-res video from NASA Goddard's Scientific Visualization Studio [ http://svs.gsfc.nasa.gov/goto?10869 ]
Racing outward at about one-quarter the speed of light, these "bullets" of ionized gas are thought to arise from a region located just outside the black hole's event horizon, the point beyond which nothing can escape.
"Like a referee at a sports game, we essentially rewound the footage on the bullets' progress, pinpointing when they were launched," said Gregory Sivakoff of the University of Alberta in Canada. He presented the findings today at the American Astronomical Society meeting in Austin, Texas. "With the unique capabilities of RXTE and the VLBA, we can associate their ejection with changes that likely signaled the start of the process."
Radio imaging by the Very Long Baseline Array (top row), combined with simultaneous X-ray observations by NASA's RXTE (middle), captured the transient ejection of massive gas "bullets" by the black hole binary H1743-322 during its 2009 outburst. By tracking the motion of these bullets with the VLBA, astronomers were able to link the ejection event to the disappearance of X-ray signals seen in RXTE data. These signals, called quasi-periodic oscillations (QPOs), vanished two days earlier than the onset of the radio flare that astronomers previously had assumed signaled the ejection.
(Credit: NRAO and NASA's Goddard Space Flight Center)
Larger image [ http://www.nasa.gov/images/content/615018main_H1743_sequence_full.jpg ]
The research centered on the mid-2009 outburst of a binary system known as H1743–322, located about 28,000 light-years away toward the constellation Scorpius. Discovered by NASA's HEAO-1 satellite in 1977, the system is composed of a normal star and a black hole of modest but unknown masses. Their orbit around each other is measured in days, which puts them so close together that the black hole pulls a continuous stream of matter from its stellar companion. The flowing gas forms a flattened accretion disk millions of miles across, several times wider than our sun, centered on the black hole. As matter swirls inward, it is compressed and heated to tens of millions of degrees, so hot that it emits X-rays.
Some of the infalling matter becomes re-directed out of the accretion disk as dual, oppositely directed jets. Most of the time, the jets consist of a steady flow of particles. Occasionally, though, they morph into more powerful outflows that hurl massive gas blobs at significant fractions of the speed of light.
This 327-MHz radio view of the center of our galaxy highlights the position of the black hole system H1743-322, as well as other features.
(Credit: J. Miller-Jones, ICRAR-Curtin Univ.; C. Brogan, NRAO)
Larger image [ http://www.nasa.gov/images/content/615015main_Finder_galcen_327MHz_labels.jpg ]
Larger image (no labels) [ http://www.nasa.gov/images/content/615016main_Finder_galcen_327MHz_nolabels.jpg ]
In early June 2009, H1743–322 underwent this transition as astronomers watched with RXTE, the VLBA, the Very Large Array near Socorro, N.M., and the Australia Telescope Compact Array (ATCA) near Narrabri in New South Wales. The observatories captured changes in the system's X-ray and radio emissions as the transformation occurred.
From May 28 to June 2, the system's X-ray and radio emissions were fairly steady, although RXTE data show that cyclic X-ray variations, known as quasi-periodic oscillations or QPOs, gradually increased in frequency over the same period. On June 4, ATCA measurements showed that the radio emission had faded significantly.
The Very Long Baseline Array is a system of ten radio telescopes spanning 5,500 miles that work together as the world's largest dedicated astronomical instrument. Each station consists of an 82-foot-diameter, 240-ton dish antenna and an adjacent control building.
Credit: NASA's Goddard Space Flight Center
Larger image [ http://www.nasa.gov/images/content/615020main_VLBA_labels.jpg ]
Larger image (no labels) [ http://www.nasa.gov/images/content/615021main_VLBA_no_labels.jpg ]
Technicians work on RXTE in 1995. Credit: NASA's Goddard Space Flight Center
Larger image [ http://www.nasa.gov/images/content/614636main_416240main_rxte-full.jpg ]
Astronomers interpret QPOs as signals produced by the interaction of clumps of ionized gas in the accretion disk near the black hole. When RXTE next looked at the system on June 5, the QPOs were gone.
The same day, the radio emission increased. An extremely detailed VLBA image revealed a bright, radio-emitting bullet of gas moving outward from the system in the direction of one of the jets. On June 6, a second blob, moving away in the opposite direction, was seen.
Until now, astronomers had associated the onset of the radio outburst with the bullet ejection event. However, based on the VLBA data, the team calculated that the bullets were launched on June 3, about two days before the main radio flare. A paper on the findings will be published in the Monthly Notices of the Royal Astronomical Society.
"This research provides new clues about the conditions needed to initiate a jet and can guide our thinking about how it happens," said Chris Done, an astrophysicist at the University of Durham, England, who was not involved in the study.
A super-sized version of the same phenomenon occurs at the center of an active galaxy, where a black hole weighing millions to billions of times our sun's mass can drive outflows extending millions of light-years.
"Black hole jets in binary star systems act as fast-forwarded versions of their galactic-scale cousins, giving us insights into how they work and how their enormous energy output can influence the growth of galaxies and clusters of galaxies," said lead researcher James Miller-Jones at the International Center for Radio Astronomy Research at Curtin University in Perth, Australia.
The Rossi X-ray Timing Explorer, which operated from Dec. 1995 to Jan. 2012, was managed by NASA's Goddard Space Flight Center in Greenbelt, Md. The VLBA, the world's largest and highest-resolution astronomical instrument, is controlled from the National Radio Astronomy Observatory's Domenici Science Operations Center.
*
Related Link
More about RXTE
http://www.nasa.gov/centers/goddard/missions/rxte.html
*
Text issued as NASA Headquarters press release No. 12-009
http://www.nasa.gov/topics/universe/features/rxte-bullets.html
===
Smallest Exoplanets Found—Each Tinier Than Earth
Rocky worlds clustered around diminutive star, astronomers say.
January 11, 2012
http://news.nationalgeographic.com/news/2012/01/120111-smallest-exoplanets-kepler-space-science/ [with comments]
===
Scientists Find More Planets Orbiting Two Stars
By SINDYA N. BHANOO
Published: January 11, 2012
In the “Star Wars” movies, Luke Skywalker’s home planet, Tatooine, orbits two suns, giving it two sunsets and two sunrises every day. In September, scientists discovered the first planet in our galaxy that does orbit two stars; now they have discovered two more and suggest that there are probably millions of these so-called circumbinary planets.
“We found two more, and that immediately tells us wow, this wasn’t a fluke,” said William Welsh, an astronomer at San Diego State University who was involved in the research. “Now that we have three, we can compare the differences and start to learn more about these as a class of planetary systems.”
Dr. Welsh and his colleagues report their discovery of the planets in the current issue of the journal Nature.
The paper describes Kepler 34b and Kepler 35b, both gaseous planets about the size of Saturn; they are 4,900 and 5,400 light years from Earth, respectively.
The planets were identified by NASA’s Kepler spacecraft, whose mission is to find other potentially habitable planets.
Life could exist on a circumbinary planet, Dr. Welsh said. The first to be discovered, Kepler 16, was just outside of what is known as the habitable zone, where liquid water, and therefore life, can exist. It is just a little too far from its suns, and too cold for life.
Kepler 34b, described in the current study, is also just outside of the habitable zone, in this case a bit too hot for life.
“That to me is interesting,” Dr. Welsh said. “It may be that we search a bit more and find that Goldilocks.”
© 2012 The New York Times Company
http://www.nytimes.com/2012/01/17/science/scientists-find-more-planets-orbiting-two-stars.html
===
Milky Way Galaxy Shown to Be Teeming With Planets
Wikimedia/Mila
By Adam Mann
January 11, 2012 | 2:06 pm
Just 20 years ago, astronomers had no direct evidence that planets orbited other stars. Now, researchers estimate the Milky Way galaxy contains a huge number of planets, with Earth-sized worlds vastly outnumbering the rest.
“We find that, on average, every star has a planet, and since there are at least 100 billion stars, there are at least 100 billion planets,” said astronomer Kailash Sahu [ http://www.stsci.edu/~ksahu/ ] of the Space Telescope Science Institute in Baltimore, Maryland, who co-authored the new study, appearing Jan. 11 in Nature.
Sahu and his team calculated this number by searching for planets using a technique called gravitational microlensing. The method works because, according to Einstein’s Theory of Relativity, a massive object bends the fabric of space-time.
Though a planet’s mass is relatively small, it is enough to curve space-time and create a “lens.” An exoplanet bends light as it passes in front of its parent star, causing a slight brightening of the star’s light.
Microlensing allows astronomers to look at a much larger sample of stars for exoplanets. Unlike other detection methods, such as looking for the slight wobble a planet exerts on its parent star, microlensing can discover planets with many different masses and distances from their star.
The team looked at roughly 30 different microlensing events and found that extrasolar planets caused three of them. Because microlensing observations are known to miss a certain percentage of planets, the researchers could use statistical analysis to get the true number of exoplanets in the galaxy.
“We think about one-sixth of stars should have a Jupiter-like planet, half have a Neptune-sized planet, and two-thirds should have an Earth,” said Sahu.
*
Previously
What Exoplanets Might Really Look Like
http://www.wired.com/wiredscience/2011/12/scientific-exoplanet-renderer/
Cold, Lonely Planets More Common Than Sun-Like Stars
http://www.wired.com/wiredscience/2011/05/cold-lonely-exoplanets/
Dark Matter Heat Could Make Exoplanets Habitable
http://www.wired.com/wiredscience/2011/03/dark-matter-planets/
Baby Exoplanets Photographed During Formation
http://www.wired.com/wiredscience/2011/02/exoplanet-baby-photos/
*
Wired.com © Condé Nast Digital
http://www.wired.com/wiredscience/2012/01/milky-way-planets/ [with comments]
===
Crowded cosmos: In Milky Way, planets more plentiful than stars, even in unexpected places
By Associated Press, Published: January 11, 2012
WASHINGTON — The more astronomers look for other worlds, the more they find that it’s a crowded and crazy cosmos. They think planets easily outnumber stars in our galaxy and they’re even finding them in the strangest of places.
And they’ve only begun to count.
Three studies released Wednesday, in the journal Nature and at the American Astronomical Society’s conference in Austin, Texas, demonstrate an extrasolar real estate boom. One study shows that in our Milky Way, most stars have planets. And since there are a lot of stars in our galaxy — about 100 billion — that means a lot of planets.
“We’re finding an exciting potpourri of things we didn’t even think could exist,” said Harvard University astronomer Lisa Kaltenegger, including planets that mirror “Star Wars” Luke Skywalker’s home planet with twin suns and a mini-star system with a dwarf sun and shrunken planets.
“We’re awash in planets where 17 years ago we weren’t even sure there were planets” outside our solar system, said Kaltenegger, who wasn’t involved in the new research.
Astronomers are finding other worlds using three different techniques and peering through telescopes in space and on the ground.
Confirmed planets outside our solar system — called exoplanets — now number well over 700, still-to-be-confirmed ones are in the thousands.
NASA’s new Kepler planet-hunting telescope in space is discovering exoplanets that are in a zone friendly to life and detecting planets as small as Earth or even tinier. That’s moving the field of looking for some kind of life outside Earth from science fiction toward just plain science.
One study in Nature this week figures that the Milky Way averages at least 1.6 large planets per star. And that is likely a dramatic underestimate.
That study is based on only one intricate and time-consuming method of planet hunting that uses several South American, African and Australian telescopes. Astronomers look for increases in brightness of distant stars that indicate planets between Earth and that pulsating star. That technique usually finds only bigger planets and is good at finding those further away from their stars, sort of like our Saturn or Uranus.
Kepler and a different ground-based telescope technique are finding planets closer to their stars. Putting those methods together, the number of worlds in our galaxy is probably much closer to two or more planets per star, said the Nature study author Arnaud Cassan of the Astrophysical Institute in Paris.
Dan Werthimer, chief scientist at the University of California Berkeley’s search for extraterrestrial intelligence program and who wasn’t part of the studies, was thrilled: “It’s great to know that there are planets out there that we can point our telescopes at.”
Kepler also found three rocky planets — tinier than Earth — that are circling a dwarf star that itself is only a bit bigger than Jupiter. They are so close to their small star that they are too hot for life.
“It’s like you took your shrink ray gun and you set it to seven times smaller and zap the planetary system,” said California Institute of Technology astronomer John Johnson, co-author of the study presented Wednesday at the astronomy conference.
Because it is so hard to see these size planets, they must be pretty plentiful, Johnson said. “It’s kind of like cockroaches. If you see one, then there are dozens hiding.”
It’s not just the number or size of planets, but where they are found. Scientists once thought systems with two stars were just too chaotic to have planets nearby. But so far, astronomers have found three different systems where planets have two suns, something that a few years ago seemed like purely “Star Wars” movie magic.
“Nature must like to form planets because it’s forming them in places that are kind of difficult to do,” said San Diego State University astronomy professor William Welsh, who wrote a study about planets with two stars that’s also published in the journal Nature.
The gravity of two stars makes the area near them unstable, Welsh said. So astronomers thought that if a planet formed in that area, it would be torn apart.
Late last year, Kepler telescope found one system with two stars. It was considered a freak. Then Welsh used Kepler to find two more. Now Welsh figures such planetary systems, while not common, are not rare either.
“It just feels like it’s inevitable that Kepler is going to come up with a habitable Earth-sized planet in the next couple of years,” Caltech’s Johnson said.
*
Online:
Nature: http://www.nature.com/nature
American Astronomical Society: http://www.aas.org
Copyright 2012 The Associated Press
http://www.washingtonpost.com/politics/crowded-cosmos-in-milky-way-planets-more-plentiful-than-stars-even-in-unexpected-places/2012/01/11/gIQAf5EDrP_story.html [with comments]
===
(linked in):
http://investorshub.advfn.com/boards/read_msg.aspx?message_id=67654755 and preceding (and any future following); http://investorshub.advfn.com/boards/read_msg.aspx?message_id=66801063 and preceding and following
http://investorshub.advfn.com/boards/read_msg.aspx?message_id=70065239 and preceding and following
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Cosmic crash. El Gordo consists of two clusters in collision, as revealed by the two separate swarms of individual galaxies (red) and the asymmetric cloud of hot, x-ray emitting gas (blue) in between.
Credit: ESO/SOAR/NASA
[ http://news.sciencemag.org/sciencenow/2012/01/when-galaxies-crash.html ]
By Alasdair Wilkins
Jan 10, 2012 11:44 AM
This galaxy cluster is nicknamed El Gordo, which means "The Fat One" in Spanish. Located seven billion light-years away, it's the biggest cluster ever found at that distance — and it's resounding proof that dark matter is everywhere in the cosmos.
The cluster is the result of two smaller clusters colliding into each other at several million miles per hour. It appears that this collision is actually pulling normal matter away from its dark counterpart, as the galaxy's hot gas has been slowed down by the collision while the dark matter keeps moving at the same speed.
Rutgers astronomer Felipe Menanteau, who led the study of this cluster, dramatically describes El Gordo as "the most massive, the hottest, and gives off the most X-rays of any cluster found so far at this distance or beyond." As the largest structures in the universe held together by gravity, galaxy clusters are an effective tool for studying the presence of dark matter and dark energy throughout the universe. Clusters will form in different ways depending on the amounts of these mysterious phenomena [which] are present at that particular point in space and time.
It's extremely rare to find a cluster as massive as El Gordo this early in the universe's life — it comes from a time when the universe was about half its present age — but everything about it completely checks out with what astronomers would expect to find based on the current model, which holds that the universe began with the Big Bang and is largely made up of dark matter and dark energy.
Via ESO [ http://www.eso.org/public/news/eso1203/ ].
*
Related Stories
Behold a galaxy twice the size of the Milky Way!
http://io9.com/5874030/behold-a-galaxy-twice-the-size-of-the-milky-way
Behold the incredible scale of Saturn
http://io9.com/5873814/behold-the-incredible-scale-of-saturn
An absolutely gorgeous shot of the International Space Station dancing with the Moon
[large image at http://cache.gawkerassets.com/assets/images/8/2012/01/d64c3c959fcc2e6248334d58fb4c8eba.jpg ]
http://io9.com/5873692/an-absolutely-gorgeous-shot-of-the-international-space-station-dancing-with-the-moon
*
Copyright 2012 io9.com
http://io9.com/5874880/super+fat-galaxy-cluster-confirms-existence-of-dark-matter-and-dark-energy [with comments]
===
Monster Galaxy Cluster 'El Gordo' Packs Mass of 2 Quadrillion Suns
10 January 2012
http://www.space.com/14192-largest-galaxy-cluster-el-gordo-photo-aas219.html [with comments] [also at http://www.csmonitor.com/Science/2012/0111/Humongous-El-Gordo-galaxy-cluster-packs-mass-of-2-quadrillion-stars (no comments yet)]
===
Hubble Survey Finds Galaxies Far, Far Away
Hubble Pinpoints Farthest Protocluster of Galaxies Ever Seen
January 10, 2012: NASA's Hubble Space Telescope has uncovered a cluster of galaxies in the initial stages of construction — the most distant such grouping ever observed in the early universe.
In a random sky survey made in near-infrared light, Hubble spied five tiny galaxies clustered together 13.1 billion light-years away. They are among the brightest galaxies at that epoch and very young, existing just 600 million years after the universe's birth in the big bang.
[ http://hubblesite.org/newscenter/archive/releases/2012/05/image/a/format/web_print/ ; http://hubblesite.org/newscenter/archive/releases/2012/05/ ]
Posted by Jason Major
January 10, 2012
The image above, a composite of visible and infrared light images captured by the Hubble Space Telescope, shows the newfound locations of five small and incredibly ancient galaxies which are in the process of merging into a galactic cluster.
Located a staggering 13.1 billion light-years away, these galaxies were in existence a mere 600 million years after the Big Bang!
This collection of infant galaxies is now the furthest — and thus oldest — known protocluster in the Universe.
Galactic clusters are particularly significant as they are the largest structures in the Universe. (Our own Milky Way is part of a cluster known as the Local Group, which contains about 45 separate galaxies.)
The distant galaxies were discovered during a random sky survey. A team led by Michele Trenti of the University of Colorado at Boulder and the Institute of Astronomy at the University of Cambridge in the UK used Hubble’s Wide Field Camera 3 (WFC3) to scan the sky in near-infrared, looking for distant sources of bright energy.
Such ancient galaxies cannot be seen in visible wavelengths, as their light has been stretched into the infrared portion of the spectrum by their ever-increasing distance.
“We need to look in many different areas because the odds of finding something this rare are very small,” said Trenti, “Typically, a region has nothing, but if we hit the right spot, we can find multiple galaxies.”
This news was announced today at the American Astronomical Society meeting in Austin, Texas. Read the official NASA release here [ http://hubblesite.org/newscenter/archive/releases/2012/05/text/ ].
Credit: NASA, ESA, M. Trenti (University of Colorado, Boulder, and Institute of Astronomy, University of Cambridge, UK), L. Bradley (STScI), and the BoRG team
© 2012 National Geographic Society
http://newswatch.nationalgeographic.com/2012/01/10/hubble-survey-finds-galaxies-far-far-away/ [with comments]
===
Our Milky Way Galaxy Is as White as, Well, Milk
January 12, 2012
http://newswatch.nationalgeographic.com/2012/01/12/our-milky-way-galaxy-is-as-white-as-well-milk/ [no comments yet]
===
Milky Way Galaxy's Past Revealed Through New Star Census
Measurements of the metal content of stars in the Milky Way's disk, using stars observed by the SEGUE-2 survey. The bottom panel shows the decrease in metal content as the distance from the galactic center increases for stars near the plane of the Milky Way disk. The metal content for stars far above the plane, shown in the upper panel, is nearly constant at all distances from the galactic center.
CREDIT: Judy Cheng and Connie Rockosi (University of California, Santa Cruz); 2MASS Survey
by Clara Moskowitz, SPACE.com Assistant Managing Editor
Date: 10 January 2012 Time: 10:14 AM ET
AUSTIN, Texas — Scientists are performing a census of the stars in the Milky Way in an effort to piece together the history of how our galaxy formed.
Researchers working on the Sloan Extension for Galactic Understanding and Exploration 2 (SEGUE-2) project, part of the Sloan Digital Sky Survey III [ http://www.space.com/10613-largest-color-sky-image-map-created-110111.html ], have now observed more than 118,000 ancient stars that were born back when our galaxy was a fraction of its present age.
"By studying these stars, we can learn what our galaxy was like when it was young, and how it grew and evolved," said Constance Rockosi, University of California, Santa Cruz astronomer and principal investigator of the SEGUE-2 project, during a presentation here on Monday (Jan. 9) at the 219th meeting of the American Astronomical Society.
For each of the 118,000 stars observed, the researchers measured positions, motions and chemical compositions. [Top 10 Star Mysteries [ http://www.space.com/24-top-10-star-mysteries.html ]]
"We put those together to try to tell the story of how the galaxy was born, and how it grew to be the way it is today," Rockosi said.
Building up metals
When the Milky Way's first stars [ http://www.space.com/12740-milky-baby-stars-growth-spurt.html ] formed, they condensed out of clouds of hydrogen and helium. Inside these stars, hydrogen and helium merged together to form the first heavy elements like carbon, nitrogen and oxygen. It was only when the most massive of these stars died in supernova explosions that some of the heavier metal elements formed [ http://www.space.com/13781-ancient-stars-galaxy-history.html ] and dispersed into surrounding space.
As subsequent generations of stars were born from this material, they contained higher concentrations of these heavy metals.
Thus, by studying stars' metal content (called metallicity), astronomers can tell how many generations of stars came before them.
The SEGUE-2 researchers used their metallicity findings to probe the history of a particular part of the Milky Way, called its disk. This is the relatively flat, pancake-shaped part of a spiral galaxy that contains its spiral arms.
Thin and thick disks
Many of the disk stars are restricted to a dense thin disk, though some stars stray above or below the plane in what's called the thick disk.
"The question we'd like to answer is, how did the thick disk form?" said Judy Cheng, University of California, Santa Cruz astronomer.
To address that question, the scientists measured how the disk stars' metallicities changed with their distances from the center of the galaxy. They found that in the thick disk, distance had no effect on metal content, but for stars in the thin disk, there was a gradient, with those in the inside of the galaxy containing more metal elements than those on the outside.
"This tells us the thin disk formed inside-out," Cheng said. The inside of the thin disk must have formed first, she explained, giving the center of the disk more time to accumulate metals from generation after generation of stars, while those in the newer, younger outside region were relatively metal-poor.
In contrast, the uniformity in metal content of the thick disk points to two possible formation scenarios for this part of our galaxy.
One possibility is that the thick disk formed all at once, leaving the metals spread evenly throughout it. Another alternative is that the thick disk used to have a metallicity gradient, but over time, and through a dynamic event such as an interaction with a smaller galaxy [ http://www.space.com/12952-milkyway-galaxy-shape-galactic-crash.html ], the stars in the thick disk got stirred up.
"It either formed rapidly or it's been mixed very well," Cheng said.
Copyright © 2012 TechMediaNetwork.com
http://www.space.com/14187-milky-disk-stars-galaxy-formation-segue.html [with comments]
===
Missing companion star indicates a Type Ia supernova came from merging dwarfs
Photograph by heritage.stsci.edu
("Finding the star in this supernova could unlock the secrets of the universe",
http://io9.com/5875677/finding-the-star-in-this-supernova-could-unlock-the-secrets-of-the-universe )
By Matthew Francis | Published January 12, 2012
Type Ia supernovae are some of the brightest explosions in the Universe, and some of the most important, since they help us measure the Universe's expansion. Nevertheless, determining exactly what is going on to produce this type of supernova has been a challenge: though white dwarfs are almost certainly involved, astronomers have yet to identify the exact process that causes one to explode. Recent analysis of Hubble Space Telescope data, performed by Bradley E. Schaefer and Ashley Pagnotta of Louisiana State University, argues strongly that at least some type Ia supernovae are the result of a merger between two white dwarfs.
A white dwarf is the dense core that remains after a relatively low-mass star like our Sun has burned through its lighter elements. The heat of fusion is no longer able to counteract a gravity-driven collapse; instead, it's balanced by quantum degeneracy pressure from the Pauli exclusion principle. If it collapsed any further, electrons would be forced into the same quantum state, which isn't possible. (This is similar to the force that keeps neutron stars [ http://arstechnica.com/science/news/2012/01/some-neutron-stars-might-shed-their-skins.ars ] from collapsing.)
There is a limit to how massive a white dwarf can be: the Chandrasekhar limit, which is about 1.4 times the mass of the Sun. If a white dwarf's mass reaches that limit, it is no longer stable. According to a widely accepted model, it then explodes as a type Ia supernova. Because white dwarfs all have similar characteristics and the same mass when they explode, their explosions should be similar. As a result, they are considered "standard candles," objects with a known intrinsic brightness. That brightness provides an independent measure of their distance, and acts as the foundation for much of modern observational cosmology, including the research behind the 2011 Nobel Prize [ http://arstechnica.com/science/news/2011/10/physics-nobel-goes-to-the-dark-side-of-the-universe.ars ] in physics.
Despite their fundamental importance to cosmology and astrophysics, how type Ia supernovae are produced is still unclear. Several significant models have been proposed, two of which are important for the current work. The double-degenerate model predicts two white dwarfs (degenerate objects) in a close binary; over time, their mutual orbit would decay through gravitational radiation until they collided.
In the single-degenerate model, a white dwarf is in a binary system with an ordinary star. The white dwarf strips gas from its companion's envelope until it has gathered enough to reach the Chandrasekhar limit, after which it explodes.
Stars are difficult to destroy; even an explosion as energetic as a type Ia supernova won't completely annihilate a companion star in a single-degenerate explosion, according to astronomers' best understanding. As Carles Badenes, a supernova researcher at the University of Pittsburgh explains, "We know the white dwarf is obliterated, but the companion star must survive, so it will still be present in the supernova remnant." But a double-degenerate type Ia supernova, since it involves an actual collision, would destroy both white dwarfs, leaving nothing but gas behind in the region where the binary once existed.
Schaefer and Pagnotta carefully analyzed the type Ia supernova remnant SNR 0509-67.5 in the Large Magellanic Cloud. It's the leftovers of an explosion that would have first been visible from Earth about 400 years ago. Any companion star that survived the blast must lie within a certain radius of the supernova's heart, or it wouldn't have been close enough to have gas pulled off by the white dwarf's gravity. The researchers carefully analyzed that region for sufficiently bright stars and star cores.
They found no candidates for a companion star brighter than an absolute magnitude of +8.4 (apparent magnitude +26.9 at that distance)—if there is a companion object, it is very faint. The nearby stars that are bright enough are too far outside the center of the supernova remnant to have fed gas into the white dwarf, the researchers concluded with a confidence of 99.7 percent. Badenes points out if this was a single-degenerate system, "That places very strong limits on the mass range of the star in the original binary system," itself an interesting result.
If the companion star is completely absent, a result consistent with the data, then maybe the double-degenerate model explains the origin of SNR 0509-67.5. In fact, no companion star has ever been identified in a type Ia supernova remnant, with the possible exception of Tycho's supernova—one's been claimed there, but its identity is disputed by many researchers. Proof of a negative is difficult, however: at best, the single case of SNR 0509-67.5 shows that the single-degenerate model doesn't apply to that event. Schaefer and Pagnotta argue that only a double-degenerate binary could be responsible for the supernova.
"Whether or not you agree with the strong conclusions [of the authors]," says Badenes, "this result is very interesting." Perhaps other type Ia supernovae are single-degenerate, but the missing massive companion star predicted by the single-degenerate model in SNR 0509-67.5 is at least consistent with a double-degenerate system. Follow-up observations of this and other type Ia supernova remnants will bring astronomers closer to an understanding of what actually causes these important explosions.
Nature, 2012 [ http://www.nature.com/nature/journal/v481/n7380/full/nature10692.html ]. DOI: 10.1038/nature10692 [ http://dx.doi.org/10.1038/nature10692 ].
Ars Technica © 2012 Condé Nast Digital
http://arstechnica.com/science/news/2012/01/the-companion-star-that-wasnt-there.ars [with comments]
===
Mystery of 400-Year-Old Star Explosion Finally Solved
11 January 2012
http://www.space.com/14202-supernova-explosion-mystery-solved-aas219.html [with comments]
===
Astrophysics: Progenitors of type Ia supernovae
Pilar Ruiz-Lapuente1
Published online11 January 2012
A study of the remains of a type Ia supernova whose light swept past Earth about 400 years ago finds no sign of a companion star. The result indicates that the supernova's progenitor was a pair of white dwarfs.
http://www.nature.com/nature/journal/v481/n7380/full/481149a.html
===
Earliest-yet observation of August supernova nails it: Destroyed star was white dwarf
Fluke observation 4 hours after star exploded allows stronger limits on size of progenitor
Public release date: 11-Jan-2012
Last year's discovery of the nearest Type Ia supernova in decades – captured only 11 hours after it exploded – allowed astronomers to finally cinch the identity of the stars behind these explosions, which have become key measures of cosmic distance.
That supernova, called SN2011fe, and presumably most Type Ia supernovae were originally white dwarfs extremely dense and compact stars composed mostly of carbon and oxygen.
Now, thanks to a much earlier, fluke observation of SN2011fe by a small robotic telescope on the island of Mallorca, University of California, Berkeley, and Lawrence Berkeley National Laboratory (LBNL) astronomers can boost confidence even higher that Type Ia supernovae originate from white dwarfs.
"A fortuitous observation only four hours after we think the star exploded allowed us to put much more constraining limits on the size of the thing that blew up," said Joshua Bloom, UC Berkeley associate professor of astronomy and first author of a paper interpreting the observation that will appear in the Jan. 10 issue of the Astrophysical Journal Letters. "The size of the progenitor is so small and the density so high, it pretty much rules out any other reasonable or even fringe possibility. This is a direct confirmation that what blew up is a carbon-oxygen white dwarf."
In 1998, two research teams used Type Ia supernovae as standard candles to conclude that the expansion of the universe is accelerating, presumably fueled by a mysterious dark energy. That discovery earned three astrophysicists, including UC Berkeley and LBNL's Saul Perlmutter, the 2011 Nobel Prize in Physics.
Bloom will present his results on Wednesday, Jan. 11, during an 11:30 a.m. CST media briefing at the national meeting of the American Astronomical Society in Austin, Texas.
Smaller than a main sequence star
Bloom and his colleagues were coauthors of two papers published Dec. 15, 2011, in the journal Nature that concluded that SN2011fe's progenitor star was a compact object with a diameter less than one-tenth that of the sun. Based on the brightness of the explosion, which occurred 21 million light years away in the Pinwheel Galaxy (M101), and the fact that the explosive debris contained large amounts of carbon and oxygen, coauthor Peter Nugent of LBNL and his colleagues concluded that before it exploded, the star was almost certainly a carbon-oxygen white dwarf.
UC Berkeley astronomer Weidong Li and colleagues concluded the same thing based on the inability of the Hubble Space Telescope to detect any star at that spot before the supernova ignited.
White dwarfs are very dense stars about the size of the Earth that burned all their hydrogen and helium into carbon and oxygen before stopping fusion altogether, destined to cool slowly into dark cinders.
After the papers were submitted to Nature in early November, UC Berkeley and LBNL astronomers learned that the 17-inch PIRATE telescope on Mallorca, operated as a remote-controlled teaching telescope by The Open University in the U.K., had obtained a deep, wide-field image of the Pinwheel Galaxy (M101) only four hours after the explosion. Because the supernova was not visible in the PIRATE image, Bloom and his colleagues, including Nugent, were able to put an even more stringent upper limit on the early brightness of the supernova.
The new analysis concludes that the progenitor star had a diameter less than one-fiftieth that of the sun – 5 to 10 times smaller than last year's limit – which implies a density 100 to 1,000 times higher.
While the previous limits ruled out hydrogen-burning main sequence stars and red giants – the most likely alternatives to a white dwarf, said Ken J. Shen, an Einstein postdoctoral fellow at LBNL and UC Berkeley – they only "placed weak constraints on smaller stars that burn helium or carbon in their cores. Only with this new observation can we now rule these out."
Looking for light from the early shock wave
UC Berkeley's Daniel Kasen, an assistant professor of physics, and Shen used theoretical models of exploding stars to estimate how bright a star of a given size would be within hours of ignition from the glow of the supernova's expanding shock wave. The bigger the star, the brighter the glow from the shock. The non-detection of the supernova four hours after it exploded enabled Kasen, Shen, Bloom and their colleagues to rule out stars larger than a white dwarf.
"This is the first time we can really be confident about what is exploding," Shen said.
Their analysis relied on theories of how a carbon-oxygen white dwarf explodes. Presumably, the white dwarf acquires mass from its binary companion until the temperature and pressure in the core rises high enough to restart fusion reactions. This time, carbon and oxygen are fused into nickel and iron in a reaction that consumes the star within seconds, blowing it up like a runaway thermonuclear bomb, Kasen said.
The first light from the explosion should be from the glow of superheated gas as the debris from the star plows through surrounding gas and dust. No one has ever caught this shockwave glow from a Type Ia supernova because it's quite dim and drops off quickly, Kasen said. The light astronomers see is from the decay of radioactive elements created in the explosion, which can shine brightly for weeks afterward.
The inability to see SN2011fe four hours after the explosion, Kasen said, allowed the team to set much more stringent limits on the size of the progenitor star.
"The earlier you get on it (the supernova), or the nearer it is, the better your chance of actually seeing the glowing outflow from the shockwave," he said. "This is the closest we've gotten. If it had been 10 instead of 20 million light years from Earth, we might have seen something four hours after the explosion."
The PIRATE observation also narrowed the limits on the companion star published last month by Li and his colleagues. The diameter of the supernova's companion must be less than one-tenth that of the sun, ruling out red giant and normal main-sequence stars.
*
Other coauthors of the ApJ Letters paper are Nathaniel R. Butler of Arizona State University; Melissa L. Graham and D. Andrew Howell of UC Santa Barbara; Ulrich Kolb, Stefan Holmes and Carole Haswell of The Open University in Milton Keynes, U.K.; Vadim Burwitz of the Max Planck Institute for Extraterrestrial Physics in Germany; Juan Rodriguez of the Astronomical Observatory of Mallorca in Spain; and Mark Sullivan of the University of Oxford.
Bloom, Nugent and others are presenting new findings during a special meeting on SN 2011fe at the AAS meeting in Austin, Texas, scheduled for 9:30 a.m. Monday, Jan. 9.
*
Contact: Robert Sanders
rsanders@berkeley.edu
510-643-6998
University of California - Berkeley
Copyright ©2012 by AAAS, the science society
http://www.eurekalert.org/pub_releases/2012-01/uoc--eoo010912.php
===
Ancient Star Explosion is Most Distant of Its Kind
Three images from the Hubble Space Telescope reveal the birth of a Type 1a supernova, a “standard candle” for measuring the expansion of the universe. Nicknamed SN Primo, this supernova is the most distant of its type ever discovered.
CREDIT: NASA, ESA, A. Riess (Space Telescope Science Institute and The Johns Hopkins University), and S. Rodney (The Johns Hopkins University)
by Nola Taylor Redd, SPACE.com ContributorDate: 12 January 2012 Time: 12:00 PM ET
Astronomers have found the most distant Type 1a supernova, a kind of star explosion that should help scientists better understand the ever-expanding universe and the nature of dark energy, the strange force accelerating that expansion.
Bursting into existence 9 billion years ago, the supernova (nicknamed SN Primo) was born from the violent death of a shrunken, super-dense star called a white dwarf [ http://www.space.com/14202-supernova-explosion-mystery-solved-aas219.html ]. Light from such explosions falls within a very narrow range, which is why astronomers call them "standard candles." As the light travels toward Earth, astronomers can measure how it is stretched by the expansion of the universe.
The team used the Wide Field Camera 3 instrument on NASA's Hubble Space Telescope to observe the supernova in near-infrared wavelengths over eight months.
"In our search for supernovae, we had gone as far as we could go in optical light," said principal investigator Adam Riess, of the Space Telescope Science Institute and Johns Hopkins University, in a statement. "But it's only the beginning of what we can do in infrared light."
The discovery was part of a survey called the CANDELS+CLASH Supernova Project. The census searches regions targeted by two large Hubble programs, the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey and the Cluster Lensing and Supernova Survey, over the course of three years, starting in 2010. SN Primo was found in October of that same year. [Supernova Photos: Great Images of Star Explosions [ http://www.space.com/11425-photos-supernovas-star-explosions.html ]]
"This discovery demonstrates that we can use the Wide Field Camera 3 to search for supernovae in the distant universe," Riess said.
The CANDLES+CLASH team searches for ancient supernovae in an effort to understand if they’ve changed over the 13.7 billion years since the Big Bang [ http://www.space.com/13320-big-bang-universe-10-steps-explainer.html ], the dramatic event that gave birth to our universe.
"If we look into the early universe and measure a drop in the supernovae, then it could be that it takes a long time to make Type 1a supernovae," said Steve Rodney, also of Johns Hopkins.
If, on the other hand, such supernovae form quickly in the early stages of the universe, they should be plentiful.
"Every supernova is unique, so it’s possible that there are multiple ways to make a supernova," Rodney said.
If the Type 1a supernovae from the early universe look different than today’s explosions, the variations could provide more insights into dark energy.
Riess was one of three astronomers awarded the 2011 Nobel Prize in Physics [ http://www.space.com/13177-nobel-prize-accelerating-universe-dark-energy-reaction.html ] for the discovery of dark energy 13 years ago by studying Type 1a supernovae.
The findings were announced at the 219th American Astronomical Society meeting in Austin, Tex., on Wednesday (Jan 11). Rodney is lead author on a paper detailing the results that has been accepted for publication by the Astrophysical Journal.
Copyright © 2012 TechMediaNetwork.com
http://www.space.com/14221-ancient-supernova-farthest-snprimo-aas219.html [no comments yet]
===
NASA'S RXTE Helps Pinpoint Launch of 'Bullets' in a Black Hole's Jet
01.10.12
Using observations from NASA's Rossi X-ray Timing Explorer (RXTE) satellite and the National Science Foundation's (NSF) Very Long Baseline Array (VLBA) radio telescope, an international team of astronomers has identified the moment when a black hole in our galaxy launched super-fast knots of gas into space.
X-ray and radio data let astronomers pinpoint when the black hole system H1743-322 ejected powerful gas 'bullets' during its mid-2009 outburst. In this animation, an X-ray hot spot in the gas around the black hole produced signals of rising frequency as the spot moved closer to the black hole. When the bullets were ejected June 3, the hot spot vanished.
[ http://www.youtube.com/watch?v=dF-KhAXbV8k (embedded)]
Download high-res video from NASA Goddard's Scientific Visualization Studio [ http://svs.gsfc.nasa.gov/goto?10869 ]
Racing outward at about one-quarter the speed of light, these "bullets" of ionized gas are thought to arise from a region located just outside the black hole's event horizon, the point beyond which nothing can escape.
"Like a referee at a sports game, we essentially rewound the footage on the bullets' progress, pinpointing when they were launched," said Gregory Sivakoff of the University of Alberta in Canada. He presented the findings today at the American Astronomical Society meeting in Austin, Texas. "With the unique capabilities of RXTE and the VLBA, we can associate their ejection with changes that likely signaled the start of the process."
Radio imaging by the Very Long Baseline Array (top row), combined with simultaneous X-ray observations by NASA's RXTE (middle), captured the transient ejection of massive gas "bullets" by the black hole binary H1743-322 during its 2009 outburst. By tracking the motion of these bullets with the VLBA, astronomers were able to link the ejection event to the disappearance of X-ray signals seen in RXTE data. These signals, called quasi-periodic oscillations (QPOs), vanished two days earlier than the onset of the radio flare that astronomers previously had assumed signaled the ejection.
(Credit: NRAO and NASA's Goddard Space Flight Center)
Larger image [ http://www.nasa.gov/images/content/615018main_H1743_sequence_full.jpg ]
The research centered on the mid-2009 outburst of a binary system known as H1743–322, located about 28,000 light-years away toward the constellation Scorpius. Discovered by NASA's HEAO-1 satellite in 1977, the system is composed of a normal star and a black hole of modest but unknown masses. Their orbit around each other is measured in days, which puts them so close together that the black hole pulls a continuous stream of matter from its stellar companion. The flowing gas forms a flattened accretion disk millions of miles across, several times wider than our sun, centered on the black hole. As matter swirls inward, it is compressed and heated to tens of millions of degrees, so hot that it emits X-rays.
Some of the infalling matter becomes re-directed out of the accretion disk as dual, oppositely directed jets. Most of the time, the jets consist of a steady flow of particles. Occasionally, though, they morph into more powerful outflows that hurl massive gas blobs at significant fractions of the speed of light.
This 327-MHz radio view of the center of our galaxy highlights the position of the black hole system H1743-322, as well as other features.
(Credit: J. Miller-Jones, ICRAR-Curtin Univ.; C. Brogan, NRAO)
Larger image [ http://www.nasa.gov/images/content/615015main_Finder_galcen_327MHz_labels.jpg ]
Larger image (no labels) [ http://www.nasa.gov/images/content/615016main_Finder_galcen_327MHz_nolabels.jpg ]
In early June 2009, H1743–322 underwent this transition as astronomers watched with RXTE, the VLBA, the Very Large Array near Socorro, N.M., and the Australia Telescope Compact Array (ATCA) near Narrabri in New South Wales. The observatories captured changes in the system's X-ray and radio emissions as the transformation occurred.
From May 28 to June 2, the system's X-ray and radio emissions were fairly steady, although RXTE data show that cyclic X-ray variations, known as quasi-periodic oscillations or QPOs, gradually increased in frequency over the same period. On June 4, ATCA measurements showed that the radio emission had faded significantly.
The Very Long Baseline Array is a system of ten radio telescopes spanning 5,500 miles that work together as the world's largest dedicated astronomical instrument. Each station consists of an 82-foot-diameter, 240-ton dish antenna and an adjacent control building.
Credit: NASA's Goddard Space Flight Center
Larger image [ http://www.nasa.gov/images/content/615020main_VLBA_labels.jpg ]
Larger image (no labels) [ http://www.nasa.gov/images/content/615021main_VLBA_no_labels.jpg ]
Technicians work on RXTE in 1995. Credit: NASA's Goddard Space Flight Center
Larger image [ http://www.nasa.gov/images/content/614636main_416240main_rxte-full.jpg ]
Astronomers interpret QPOs as signals produced by the interaction of clumps of ionized gas in the accretion disk near the black hole. When RXTE next looked at the system on June 5, the QPOs were gone.
The same day, the radio emission increased. An extremely detailed VLBA image revealed a bright, radio-emitting bullet of gas moving outward from the system in the direction of one of the jets. On June 6, a second blob, moving away in the opposite direction, was seen.
Until now, astronomers had associated the onset of the radio outburst with the bullet ejection event. However, based on the VLBA data, the team calculated that the bullets were launched on June 3, about two days before the main radio flare. A paper on the findings will be published in the Monthly Notices of the Royal Astronomical Society.
"This research provides new clues about the conditions needed to initiate a jet and can guide our thinking about how it happens," said Chris Done, an astrophysicist at the University of Durham, England, who was not involved in the study.
A super-sized version of the same phenomenon occurs at the center of an active galaxy, where a black hole weighing millions to billions of times our sun's mass can drive outflows extending millions of light-years.
"Black hole jets in binary star systems act as fast-forwarded versions of their galactic-scale cousins, giving us insights into how they work and how their enormous energy output can influence the growth of galaxies and clusters of galaxies," said lead researcher James Miller-Jones at the International Center for Radio Astronomy Research at Curtin University in Perth, Australia.
The Rossi X-ray Timing Explorer, which operated from Dec. 1995 to Jan. 2012, was managed by NASA's Goddard Space Flight Center in Greenbelt, Md. The VLBA, the world's largest and highest-resolution astronomical instrument, is controlled from the National Radio Astronomy Observatory's Domenici Science Operations Center.
*
Related Link
More about RXTE
http://www.nasa.gov/centers/goddard/missions/rxte.html
*
Text issued as NASA Headquarters press release No. 12-009
http://www.nasa.gov/topics/universe/features/rxte-bullets.html
===
Smallest Exoplanets Found—Each Tinier Than Earth
Rocky worlds clustered around diminutive star, astronomers say.
January 11, 2012
http://news.nationalgeographic.com/news/2012/01/120111-smallest-exoplanets-kepler-space-science/ [with comments]
===
Scientists Find More Planets Orbiting Two Stars
By SINDYA N. BHANOO
Published: January 11, 2012
In the “Star Wars” movies, Luke Skywalker’s home planet, Tatooine, orbits two suns, giving it two sunsets and two sunrises every day. In September, scientists discovered the first planet in our galaxy that does orbit two stars; now they have discovered two more and suggest that there are probably millions of these so-called circumbinary planets.
“We found two more, and that immediately tells us wow, this wasn’t a fluke,” said William Welsh, an astronomer at San Diego State University who was involved in the research. “Now that we have three, we can compare the differences and start to learn more about these as a class of planetary systems.”
Dr. Welsh and his colleagues report their discovery of the planets in the current issue of the journal Nature.
The paper describes Kepler 34b and Kepler 35b, both gaseous planets about the size of Saturn; they are 4,900 and 5,400 light years from Earth, respectively.
The planets were identified by NASA’s Kepler spacecraft, whose mission is to find other potentially habitable planets.
Life could exist on a circumbinary planet, Dr. Welsh said. The first to be discovered, Kepler 16, was just outside of what is known as the habitable zone, where liquid water, and therefore life, can exist. It is just a little too far from its suns, and too cold for life.
Kepler 34b, described in the current study, is also just outside of the habitable zone, in this case a bit too hot for life.
“That to me is interesting,” Dr. Welsh said. “It may be that we search a bit more and find that Goldilocks.”
© 2012 The New York Times Company
http://www.nytimes.com/2012/01/17/science/scientists-find-more-planets-orbiting-two-stars.html
===
Milky Way Galaxy Shown to Be Teeming With Planets
Wikimedia/Mila
By Adam Mann
January 11, 2012 | 2:06 pm
Just 20 years ago, astronomers had no direct evidence that planets orbited other stars. Now, researchers estimate the Milky Way galaxy contains a huge number of planets, with Earth-sized worlds vastly outnumbering the rest.
“We find that, on average, every star has a planet, and since there are at least 100 billion stars, there are at least 100 billion planets,” said astronomer Kailash Sahu [ http://www.stsci.edu/~ksahu/ ] of the Space Telescope Science Institute in Baltimore, Maryland, who co-authored the new study, appearing Jan. 11 in Nature.
Sahu and his team calculated this number by searching for planets using a technique called gravitational microlensing. The method works because, according to Einstein’s Theory of Relativity, a massive object bends the fabric of space-time.
Though a planet’s mass is relatively small, it is enough to curve space-time and create a “lens.” An exoplanet bends light as it passes in front of its parent star, causing a slight brightening of the star’s light.
Microlensing allows astronomers to look at a much larger sample of stars for exoplanets. Unlike other detection methods, such as looking for the slight wobble a planet exerts on its parent star, microlensing can discover planets with many different masses and distances from their star.
The team looked at roughly 30 different microlensing events and found that extrasolar planets caused three of them. Because microlensing observations are known to miss a certain percentage of planets, the researchers could use statistical analysis to get the true number of exoplanets in the galaxy.
“We think about one-sixth of stars should have a Jupiter-like planet, half have a Neptune-sized planet, and two-thirds should have an Earth,” said Sahu.
*
Previously
What Exoplanets Might Really Look Like
http://www.wired.com/wiredscience/2011/12/scientific-exoplanet-renderer/
Cold, Lonely Planets More Common Than Sun-Like Stars
http://www.wired.com/wiredscience/2011/05/cold-lonely-exoplanets/
Dark Matter Heat Could Make Exoplanets Habitable
http://www.wired.com/wiredscience/2011/03/dark-matter-planets/
Baby Exoplanets Photographed During Formation
http://www.wired.com/wiredscience/2011/02/exoplanet-baby-photos/
*
Wired.com © Condé Nast Digital
http://www.wired.com/wiredscience/2012/01/milky-way-planets/ [with comments]
===
Crowded cosmos: In Milky Way, planets more plentiful than stars, even in unexpected places
By Associated Press, Published: January 11, 2012
WASHINGTON — The more astronomers look for other worlds, the more they find that it’s a crowded and crazy cosmos. They think planets easily outnumber stars in our galaxy and they’re even finding them in the strangest of places.
And they’ve only begun to count.
Three studies released Wednesday, in the journal Nature and at the American Astronomical Society’s conference in Austin, Texas, demonstrate an extrasolar real estate boom. One study shows that in our Milky Way, most stars have planets. And since there are a lot of stars in our galaxy — about 100 billion — that means a lot of planets.
“We’re finding an exciting potpourri of things we didn’t even think could exist,” said Harvard University astronomer Lisa Kaltenegger, including planets that mirror “Star Wars” Luke Skywalker’s home planet with twin suns and a mini-star system with a dwarf sun and shrunken planets.
“We’re awash in planets where 17 years ago we weren’t even sure there were planets” outside our solar system, said Kaltenegger, who wasn’t involved in the new research.
Astronomers are finding other worlds using three different techniques and peering through telescopes in space and on the ground.
Confirmed planets outside our solar system — called exoplanets — now number well over 700, still-to-be-confirmed ones are in the thousands.
NASA’s new Kepler planet-hunting telescope in space is discovering exoplanets that are in a zone friendly to life and detecting planets as small as Earth or even tinier. That’s moving the field of looking for some kind of life outside Earth from science fiction toward just plain science.
One study in Nature this week figures that the Milky Way averages at least 1.6 large planets per star. And that is likely a dramatic underestimate.
That study is based on only one intricate and time-consuming method of planet hunting that uses several South American, African and Australian telescopes. Astronomers look for increases in brightness of distant stars that indicate planets between Earth and that pulsating star. That technique usually finds only bigger planets and is good at finding those further away from their stars, sort of like our Saturn or Uranus.
Kepler and a different ground-based telescope technique are finding planets closer to their stars. Putting those methods together, the number of worlds in our galaxy is probably much closer to two or more planets per star, said the Nature study author Arnaud Cassan of the Astrophysical Institute in Paris.
Dan Werthimer, chief scientist at the University of California Berkeley’s search for extraterrestrial intelligence program and who wasn’t part of the studies, was thrilled: “It’s great to know that there are planets out there that we can point our telescopes at.”
Kepler also found three rocky planets — tinier than Earth — that are circling a dwarf star that itself is only a bit bigger than Jupiter. They are so close to their small star that they are too hot for life.
“It’s like you took your shrink ray gun and you set it to seven times smaller and zap the planetary system,” said California Institute of Technology astronomer John Johnson, co-author of the study presented Wednesday at the astronomy conference.
Because it is so hard to see these size planets, they must be pretty plentiful, Johnson said. “It’s kind of like cockroaches. If you see one, then there are dozens hiding.”
It’s not just the number or size of planets, but where they are found. Scientists once thought systems with two stars were just too chaotic to have planets nearby. But so far, astronomers have found three different systems where planets have two suns, something that a few years ago seemed like purely “Star Wars” movie magic.
“Nature must like to form planets because it’s forming them in places that are kind of difficult to do,” said San Diego State University astronomy professor William Welsh, who wrote a study about planets with two stars that’s also published in the journal Nature.
The gravity of two stars makes the area near them unstable, Welsh said. So astronomers thought that if a planet formed in that area, it would be torn apart.
Late last year, Kepler telescope found one system with two stars. It was considered a freak. Then Welsh used Kepler to find two more. Now Welsh figures such planetary systems, while not common, are not rare either.
“It just feels like it’s inevitable that Kepler is going to come up with a habitable Earth-sized planet in the next couple of years,” Caltech’s Johnson said.
*
Online:
Nature: http://www.nature.com/nature
American Astronomical Society: http://www.aas.org
Copyright 2012 The Associated Press
http://www.washingtonpost.com/politics/crowded-cosmos-in-milky-way-planets-more-plentiful-than-stars-even-in-unexpected-places/2012/01/11/gIQAf5EDrP_story.html [with comments]
===
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