Author	Topic:   Astronomy - Extra-Solar
Dying Star Reveals Planets With Water (Moderator)	posted 9/18/03 11:27 AM     Dying star reveals planets with water 12:19 12 July 01 newscientist.com A dying star has provided astronomers with their first view of water in a planetary system outside our own. The sighting provides hard evidence that our solar system is not unusual in harbouring the ingredients for life. Infra-red astronomy has already produced pictures of dusty planetary discs orbiting young stars, which theory predicts should coalesce into planets like those in our own solar system. Although some of these systems contain signs of water vapour, astronomers always assumed the water was from the young stars, which are made of hydrogen. NASA Now NASA's Submillimetre Wave Astronomy Satellite has produced the first evidence of water vapour orbiting the brightest star in the night sky, a red giant called CW Leonis. Because CW Leonis contains no hydrogen, astronomers expected it to produce very little water, less than one ten thousandth of the amount SWAS actually saw. Gary Melnick from the Harvard-Smithsonian Centre for Astrophysics in Cambridge and colleagues on the SWAS team believe the water vapour must have come from planets or comets that orbited the star. Planets engulfed Subscribe to New Scientist for more news and features Related Stories Planets common around brown dwarfs, but extremely inhospitable 8 June 2001 Most stars may only be orbited by small, barren worlds 26 April 2001 Planets like Earth could be commonplace in the Universe 20 February 2001 For more related stories search the print edition Archive Weblinks SWAS, Harvard SWAS, NASA This probably happened when CW Leonis began to burn heavy, energetic elements and swelled out to engulf planets and comets in its outer planetary disc. "We can expect CW Leonis had a fully developed planetary system," agrees Alan Boss, who models solar system evolution at the Carnegie Institute in Washington DC. Most of the water currently around CW Leonis probably comes from icy bodies orbiting beyond the region that its former planets inhabited. These have now been engulfed by the growing star. In our solar system, much of the water is stored in the Kuiper belt, a belt of icy bodies that orbit beyond the planet Pluto. CW Leonis is now large enough to start heating the entire Kuiper belt, boiling thousands of comets. "We are witnessing the apocalyse that will befall our own solar system," says Melnick. Boss is especially excited by the SWAS find because it reveals a new capability to sample distant solar systems at different stages of their life cycle. This will enable astronomers to work out just how typical our system is, and what chance there is that conditions suitable for life have evolved elsewhere. Eugenie Samuel http://www.newscientist.com/news/news.jsp?id=Ns99991008
Tantalising evidence hints Universe is finite (Moderator)	posted 10/11/03 9:24 AM     Thursday October 9, 04:00 PM Tantalising evidence hints Universe is finite By Hazel Muir Perplexing observations beamed back by a NASA spacecraft are fuelling debates about a mystery of biblical proportions - is our Universe infinite? Scientists have announced tantalising hints that the Universe is actually relatively small, with a hall-of-mirrors illusion tricking us into thinking that space stretches on forever. However, work by a second team seems to contradict this, and scientists are now busy trying to resolve the conundrum. "Whether space is finite is something people have been asking since ancient times, and probably before that," says mathematician Jeffrey Weeks from Canton, New York. "If we resolved this and confirmed that space is finite, this would be an enormous step forward in our understanding of nature." At the centre of the debate are observations by NASA's Wilkinson Microwave Anisotropy Probe (WMAP), which was launched in 2001. The probe measures temperature ripples in the "cosmic microwave background", the afterglow radiation from the big bang fireball. Astronomers are interested in how strong different sizes of ripples are, as this reveals vital information about the early Universe, and might tell us how big the Universe is today. Many astronomers suspect that the Universe is infinite. In that case, the microwave background ripples should have an unlimited range of sizes. But while WMAP's observations of small-scale ripples have matched predictions for an infinite Universe almost perfectly, the large-scale measurements have not. On the largest scales, WMAP has shown that the ripples almost disappear (see graphic, top). Hall of mirrors It could just be down to chance. Computer simulations that model the birth of the microwave background create this pattern once every few hundred runs. But it could mean that space itself is not big enough to support the broadest ripples, according to Weeks. "Just as the vibrations of a bell cannot be larger than the bell itself, any fluctuations in space cannot be larger than space itself," he says. Weeks and his colleagues, a team of astrophysicists in France, say the WMAP results suggest that the Universe is not only small, but that space wraps back on itself in a bizarre way ( Nature , vol 425, p 593). Despite being finite, the Universe would not have any kind of edge. If a spacecraft blasted off in what we'd perceive to be a straight line - the line a beam of light would follow - it would eventually end up back where it started. Because of this odd wraparound effect, the light from one galaxy could follow two different routes to the Earth, so the same galaxy would appear in two different parts of the sky. Effectively, the Universe would be like a hall of mirrors, with the wraparound effect producing multiple images of everything inside. Identical pentagons According to Weeks, the WMAP results point to a very specific illusion - that our Universe seems like an endlessly repeating set of dodecahedrons, football-like shapes with a surface of 12 identical pentagons. If you exit the football through one pentagon, you re-enter the same region through the opposite face and you keep meeting the same galaxies over and over again (see graphic, bottom). Weeks says the match between the predictions of his repeating-football model and the WMAP observations is striking: "I was just blown away, the results are far better than I could have imagined." If confirmed, they would indeed be stunning. They would mean that the Universe is relatively small, something like 70 billion light years across. What's more, we could in theory see the entire cosmos and check that there are no hidden corners where the laws of physics are different. For instance, it would rule out exotic ideas such as chaotic inflation, which suggests our local Universe is just one of myriad expanding bubbles beyond eyeshot, each with slightly different physical laws. It would also banish the philosophical paradoxes of an infinite Universe, such as the idea that every person on Earth has an infinite number of alien doubles leading parallel lives. "If we could prove that the Universe was finite and small, that would be earth-shattering," says David Spergel of Princeton University in New Jersey. "It would really change our view of the Universe." Matching circles However, in response to Weeks's report, Spergel and his colleagues have announced evidence that contradicts the findings. They showed previously that if the Universe does produce a hall-of-mirrors effect, it should be possible to find a pattern of matching circles in the microwave background around which the fluctuations are identical ( New Scientist print edition, 19 September 1998, p 28). Weeks's theory predicts six specific pairs of matching circles in the sky, but Spergel's team has had no luck finding them in WMAP data. "Weeks's team has a very powerful model that's nice because it makes a very specific prediction about the pattern we should see on the sky," says Spergel. "However, we've looked for it, and we don't see it." Spergel and his team are now working with Weeks to see if they might somehow have missed the circles. And there is a further test of the dodecahedron model. It predicts that a key measure of the density of matter in the Universe, which governs its curvature, is equal to 1.013. Completely flat space corresponds to 1, while values greater than or less than 1 would create a curved Universe. Observations of the microwave background radiation so far suggest the value lies somewhere between 1.00 and 1.04. Further observations by WMAP and other instruments should give a more accurate answer within the next few months. Supercomputer cycles In the meantime, Spergel's team is continuing to use the matching-circles technique to see whether the Universe might be small and finite but with some other possible shape. Computers at two universities and at NASA's Goddard Space Flight Center are scanning the WMAP results for all the possible patterns of circles that might exist on the microwave background. "We're burning up a lot of supercomputer cycles on this," says Spergel's colleague Neil Cornish of Montana State University in Bozeman. Cornish says his team believes it has already ruled out almost half of the possible small-Universe shapes - including football and doughnut shapes - and he suspects the work will probably turn up nothing, meaning that the Universe is either very large or infinite. "We're disappointed because we favoured the small-Universe idea," says Cornish. "But I guess you've just got to take the Universe you're given." http://uk.news.yahoo.com/031009/12/eaok9.html
Could Space Signal Be Alien Contact?	posted 9/2/04 1:28 PM     Science - Reuters Could Space Signal Be Alien Contact? 39 minutes ago LONDON (Reuters) - An unexplained radio signal from deep space could -- just might be -- contact from an alien civilization, New Scientist magazine reported on Thursday. The signal, coming from a point between the Pisces and Aries constellations, has been picked up three times by a telescope in Puerto Rico. New Scientist said the signal could be generated by a previously unknown astronomical phenomenon or even be a by-product from the telescope itself. But the mystery beam has excited astronomers across the world. "If they can see it four, five or six times it really begins to get exciting," Jocelyn Bell Burnell of the University of Bath in western England told the magazine. It was broadcast on the main frequency at which the universe's most common element, hydrogen, absorbs and emits energy, and which astronomers say is the most likely means by which aliens would advertise their presence. The potentially extraterrestrial signals were picked up through the SETI@home project, which uses programs running as screensavers on millions of personal computers worldwide to sift through the huge amount of data picked up by the telescope. http://story.news.yahoo.com/news?tmpl=story&cid=585&e=1&u=/nm/20040902/sc_nm/space_signals_dc
Mysterious signals from 1000 light years away	posted 9/3/04 2:21 AM     Mysterious signals from 1000 light years away 19:00 01 September 04 In February 2003, astronomers involved in the search for extraterrestrial intelligence (SETI) pointed the massive radio telescope in Arecibo, Puerto Rico, at around 200 sections of the sky. The same telescope had previously detected unexplained radio signals at least twice from each of these regions, and the astronomers were trying to reconfirm the findings. The team has now finished analysing the data, and all the signals seem to have disappeared. Except one, which has got stronger. This radio signal, now seen on three separate occasions, is an enigma. It could be generated by a previously unknown astronomical phenomenon. Or it could be something much more mundane, maybe an artefact of the telescope itself. But it also happens to be the best candidate yet for a contact by intelligent aliens in the nearly six-year history of the SETI@home project, which uses programs running as screensavers on millions of personal computers worldwide to sift through signals picked up by the Arecibo telescope. Absorb and emit “It’s the most interesting signal from SETI@home,” says Dan Werthimer, a radio astronomer at the University of California, Berkeley (UCB) and the chief scientist for SETI@home. “We’re not jumping up and down, but we are continuing to observe it.” Named SHGb02+14a, the signal has a frequency of about 1420 megahertz. This happens to be one of the main frequencies at which hydrogen, the most common element in the universe, readily absorbs and emits energy. Some astronomers have argued that extraterrestrials trying to advertise their presence would be likely to transmit at this frequency, and SETI researchers conventionally scan this part of the radio spectrum. SHGb02+14a seems to be coming from a point between the constellations Pisces and Aries, where there is no obvious star or planetary system within 1000 light years. And the transmission is very weak. “We are looking for something that screams out ‘artificial’,” says UCB researcher Eric Korpela, who completed the analysis of the signal in April. “This just doesn’t do that, but it could be because it is distant.” Unknown signature The telescope has only observed the signal for about a minute in total, which is not long enough for astronomers to analyse it thoroughly. But, Korpela thinks it unlikely SHGb02+14a is the result of any obvious radio interference or noise, and it does not bear the signature of any known astronomical object. That does not mean that only aliens could have produced it. “It may be a natural phenomenon of a previously undreamed-of kind like I stumbled over,” says Jocelyn Bell Burnell of the University of Bath, UK. It was Bell Burnell who in 1967 noticed a pulsed radio signal which the research team at the time thought was from extraterrestrials but which turned out to be the first ever sighting of a pulsar. There are other oddities. For instance, the signal’s frequency is drifting by between eight to 37 hertz per second. “The signal is moving rapidly in frequency and you would expect that to happen if you are looking at a transmitter on a planet that’s rotating very rapidly and where the civilisation is not correcting the transmission for the motion of the planet,” Korpela says. This does not, however, convince Paul Horowitz, a Harvard University astronomer who looks for alien signals using optical telescopes. He points out that the SETI@home software corrects for any drift in frequency. Fishy and puzzling The fact that the signal continues to drift after this correction is “fishy”, he says. “If [the aliens] are so smart, they’ll adjust their signal for their planet’s motion.” The relatively rapid drift of the signal is also puzzling for other reasons. A planet would have to be rotating nearly 40 times faster than Earth to have produced the observed drift; a transmitter on Earth would produce a signal with a drift of about 1.5 hertz per second. What is more, if telescopes are observing a signal that is drifting in frequency, then each time they look for it they should most likely encounter it at a slightly different frequency. But in the case of SHGb02+14a, every observation has first been made at 1420 megahertz, before it starts drifting. “It just boggles my mind,” Korpela says. The signal could be an artefact that, for some reason, always appears to be coming from the same point in the sky. The Arecibo telescope has a fixed dish reflector and scans the skies by changing the position of its receiver relative to the dish. When the receiver reaches a certain position, it might just be able to reflect waves from the ground onto the dish and then back to itself, making it seem as if the signal was coming from space. “Perhaps there is an object on the ground near the telescope emitting at about this frequency,” Korpela says. This could be confirmed by using a different telescope to listen for SHGb02+14a. Possible fraud There is also the possibility of fraud by someone hacking the SETI@home software to make it return evidence for an extraterrestrial transmission. However, SHGb02+14a was seen on two different occasions by different SETI@home users, and those calculations were confirmed by others. Then the signal was seen a third time by the SETI@home researchers. The unusual characteristics of the signal also make it unlikely that someone is playing a prank, Korpela says. “As I can’t think of any way to make a signal like this, I can’t think of any way to fake it.” David Anderson, director of SETI@home, remains sceptical but curious about the signal. ”It’s unlikely to be real but we will definitely be re-observing it.” Bell Burnell agrees that it is worth persisting with. “If they can see it four, five or six times it really begins to get exciting,” she says. It is already exciting for IT engineers Oliver Voelker of Logpoint in Nuremberg, Germany and Nate Collins of Farin and Associates in Madison, Wisconsin, who found the signal. Collins wonders how his bosses will react to company computers finding aliens. “I might have to explain a little further about just how much I was using [the computers],” he says. Eugenie Samuel Reich http://www.newscientist.com/news/news.jsp?id=ns99996341
Scientist says alien signal story is hype	posted 9/3/04 1:59 PM     Scientist says alien signal story is hype Paul Nettleton and Sam Jones Thursday September 2, 2004 The Guardian Excitable reports that the search for a radio signal from ET has paid off were dismissed as premature by astronomers involved in the search for extra-terrestrial intelligence (Seti). The tantalising claim that a signal picked up by the Arecibo radio telescope three times for a total of less than a minute last year could be the best candidate yet for success in the six-year Seti@home project, in which a screensaver program on millions of home computers sifts through raw data, appeared in New Scientist magazine. But Dan Wertheimer, the project's chief scientist and a radio astronomer at the University of Cailfornia, Berkeley, who was quoted by the magazine as saying "it's the most interesting signal from Seti@home", told BBC News Online: "It's all hype and noise. We have nothing that is unusual. It's all out of proportion." The signal, named SHGbo2+14a, has a frequency of about 1420MHz, one of the main frequencies at which hydrogen, the most common element in the universe, absorbs and emits energy. Some scientists say aliens trying to introduce themselves would be likely to transmit at this frequency. Computers running in the US and Germany detected the signal, which appears to be coming from between the constellations Pisces and Aries, where there is no obvious star or planetary system within 1,000 light years. It has a rapidly fluctuating frequency, which could occur if it was beamed out from a rapidly spinning planet or object, although a planet would have to be rotating nearly 40 times faster than Earth to produce the same drift. A drifting signal would be expected to have a different frequency each time it was detected. Yet with every observation of SHGbo2+14a, the signal has started off with a frequency of 1420MHz before starting to drift - although this could be connected to the telescope. Speaking from the Aricebo site in Puerto Rico, Dr Wertheimer added: "We have no candidates that we are particularly excited about." After analysing 50 trillion frequency bands, he added, it was not surprising that a signal like SHGbo2+14a should occur by chance. http://www.guardian.co.uk/life/news/story/0,12976,1295799,00.html
NASA Tracks Three Space Bursts, Says Stellar Explosions Imminent	posted 10/2/04 10:52 AM     NASA Tracks Three Space Bursts, Says Stellar Explosions Imminent Fri Oct 1, 4:37 PM ET Science - Space.com Robert Roy Britt Senior Science Writer SPACE.com Updated at 2:54 p.m. ET Three powerful bursts of energy from different regions of space could presage spectacular explosions of huge stars, astronomers just announced. The eruptions are likely imminent. Scientists around the world are scrambling to track the blasts, NASA (news - web sites) officials said last night. There is no danger to Earth from the expected stellar explosions, called supernovas. Yet never before have astronomers had such advance warning of the faraway explosions. In fact, they don't even know if their forecasts are right. What is clear is that as the flashes develop into explosions -- or not -- knowledge of how stars die is likely to grow. 'Beautiful' bursts A blast of X-rays was spotted Sept. 12, and another on Sept. 16. Each came from a different location in the sky and from galaxies far beyond our own. A more powerful eruption was detected Sept. 24 from yet another spot in the sky. This third flash, importantly, was on the verge between an X-ray eruption and a more energetic gamma-ray burst, which involves a more powerful form of radiation. X-rays and gamma rays are types of light, just like less powerful visible light and lowly radio waves. All are part of the electromagnetic spectrum. The three high-energy flashes were each discovered by NASA's orbiting High-Energy Transient Explorer (HETE- 2) observatory. There is no reason to suspect there's any connection between the three blasts. "We think it's just a strange coincidence," George Ricker, of the Massachusetts Institute of Technology (news - web sites), said in a telephone interview today. Telescopes around the world have since raced to track each event. "Each burst has been beautiful," Ricker said. "Depending on how these evolve, they could support important theories about supernova[s] and gamma-ray bursts." Ricker told SPACE.com the stars will likely go supernova 10 to 20 days after the initial bursts that were spotted. The initial events have faded beyond the visibility of small professional telescopes and are now being monitored by some of the world's largest ground-based observatories. Backyard astronomers likely could not find the bursts, Ricker said. Head-scratchers Gamma-ray bursts are the most energetic events in the universe other than the Big Bang. They briefly outshine entire galaxies. Astronomers think each burst is related to the explosion of a very massive star that has used up its main fuel. Much material is blasted into space, and some falls back rapidly and collapses into a tiny sphere more dense than most folks can imagine, resulting in the formation of a black hole. In some cases, however, the energy might be unleashed when two black holes collide. But experts are not sure why some supernovas are accompanied by gamma-ray bursts and others seem to shoot out only X-rays (the latter assumption has not even been convincingly determined). The leading theory is that when a star collapses after exploding, it sends out two incredibly swift jets of material, one along each of its poles. If a jet is pointed toward Earth, the thinking goes, we see a gamma-ray burst. Otherwise we note only the X rays. Other theorists argue that gamma-ray bursts and X-ray flashes are different animals altogether. All this could become much clearer in coming days as the three new eruptions are monitored by a global telescope network designed to detect each of the different wavelengths of energy involved. Nature on a rampage The eruptions are all probably a billion or so light-year away, Ricker said. That's relatively close in comparison to most gamma-ray bursts, which may explain why the X-ray flashes have been seen at all. "These past two weeks have been like 'cock, fire, reload,'" Ricker said. "Nature keeps on delivering." Until recently, the events leading up to gamma-ray bursts and black hole formation had not been seen. The bursts are known to come routinely from every direction in the sky. But they last just seconds, sometimes less than a second, so in most cases only the aftermath is witnessed. Astronomers hope this time they've seen the prelude and can witness the entire process. Observations of other events in recent years linked gamma-ray bursts to supernovas. Now, follow-up observations of the Sept. 24 blast, named GRB040924, suggests X-rays and gamma rays do indeed emanate from the same event. The recent bursts "may be the first time we see an X-ray flash lead to a supernova," said theorist Stanford Woosley of the University of California at Santa Cruz. http://story.news.yahoo.com/news?tmpl=story&cid=96&e=1&u=/space/20041001/sc_space/nasatracksthreespaceburstssaysstellarexplosionsimminent
Monster star burst was brighter than full Moon: astronomers (Moderator)	posted 2/19/05 12:57 AM     Friday February 18, 07:23 PM Monster star burst was brighter than full Moon: astronomers PARIS (AFP) - Stunned astronomers described the greatest cosmic explosion ever monitored -- a star burst from the other side of the galaxy that was briefly brighter than the full Moon and swamped satellites and telescopes. The high-radiation flash, detected last December 27, caused no harm to Earth but would have literally fried the planet had it occurred within a few light years of home. Normally reserved skywatchers struggled for superlatives. "This is a once-in-a-lifetime event," said Rob Fender of Britain's Southampton University. "We have observed an object only 20 kilometers (12 miles) across, on the other side of our galaxy, releasing more energy in a 10th of a second than the Sun emits in 100,000 years." "It was the mother of all magnetic flares -- a true monster," said Kevin Hurley, a research physicist at the University of California at Berkeley. Bryan Gaensler of the United States' Harvard-Smithsonian Center for Astrophysics, described the burst as "maybe a once per century or once per millennium event in our galaxy. "Astronomically speaking, this explosion happened in our backyard. If it were in our living room, we'd be in big trouble." The blast was caused by an eruption on the surface of a known, exotic kind of neutron star called SGR 1806-20, located about 50,000 light years from Earth in the constellation of Sagittarius and about three billion times farther from us than the Sun. A neutron star is the remnant of a very large star near the end of its life -- a tiny, extraordinarily dense core with a powerful magnetic field, spinning swiftly on its axis. When these ancient star cores finally run out of fuel, they collapse in on themselves and explode as a supernova. There are millions of neutron stars in the Milky Way but, so far, only a dozen have been found to be "magnetars": neutron stars with an ultra-powerful magnetic field. Magnetars have have a magnetic field measuring about 1,000 trillion gauss, hundreds of times more powerful than that of any other object in the Universe. To give an idea of this in earthly terms, the field is so powerful that it could strip the data off a credit card at a distance of 200,000 kilometers (120,000 miles). SGR 1806-20 is an even rarer bird. It is one of only four known "soft gamma repeater" (SGR) magnetars, so called because they flare up randomly and release gamma rays in a mammoth burst. Why this happens is unknown. One theory is that the energy release comes from magnetic fields which wrestle and overlap because of the star's spin and then snap back and reconnect, creating a "starquake" rather like the competing faults that cause an earthquake. What is sure, though, is that the outpouring of energy is massive. The SGR 1806-20 spewed out about 10,000 trillion trillion watts, or about 100 times brighter than any of the several "giant flares" that have been previously recorded. Despite this energy loss, the strange star did not even pause, Britain's Royal Astronomical Society (RAS) said. "SGR 1806-20 spins once in only 7.5 seconds. Amazingly, the December 27 event did not cause any slowing of its spin rate, as would be expected," the RAS said. The flare, detected by satellites and telescopes operated by NASA and Europe, was so powerful that it bounced off the Moon and lit up the Earth's upper atmosphere. For over a tenth of the second, it was actually brighter than a full Moon, and briefly overwhelmed delicate sensors, RAS said. Two science teams, formed by observations provided by 20 institutes around the world, will report on the blast in a forthcoming issue of the British weekly journal Nature. Many questions will be thrown up by the event, including the intriguing speculation that the dinosaurs may have been wiped out by a similar, closer gamma-ray explosion 65 million years ago, and not by climate change inflicted by an asteroid impact. "Had this happened within 10 light years of us, it would have severly damaged our atmosphere and possibly have triggered a mass extinction," said lead-author Gaensler. The good news, he noted, is that the nearest known magnetar to Earth, 1E 2259+586, is about 13,000 light years away. http://uk.news.yahoo.com/050218/323/fcszr.html
Leaking Gravity May Explain Cosmic Puzzle (Moderator)	posted 3/1/05 6:12 AM     Leaking Gravity May Explain Cosmic Puzzle By Sara Goudarzi Special to SPACE.com posted: 28 February 2005 06:28 am ET WASHINGTON, D.C. - Scientists may not have to go over to the dark side to explain the fate of the universe. The theory that the accelerated expansion of the universe is caused by mysterious "dark energy" is being challenged by New York University physicist Georgi Dvali. He thinks there's just a gravity leak. Scientists have known since the 1920s that the universe is expanding. In the late 1990s, they realized that it is expanding at an ever-increasing pace. At a loss to explain the stunning discovery, cosmologists blamed it on dark energy, a newly coined term to describe the mysterious antigravity force apparently pushing galaxies outward. This repulsive, unknown force is believed to make up more than 70 percent of the mass-energy budget of the universe. But the existence of dark energy is far from proven, and some researchers believe they and their colleagues simply don't understand gravity at larger scales. The gravitational pull between any two objects becomes less with distance. But in Dvali's view, it weakens more than standard theory predicts. Dvali would modify the theory of gravity so that the universe becomes self-accelerating, eliminating the need for dark energy. He presented his work here earlier this month at the annual meeting of the American Association for the Advancement of Science. Dvali borrows from string theory, which states that there are extra, hidden dimensions beyond the four we are familiar with: three directions and time. String theory suggests that gravitons -- hypothetical elementary particles transmitting gravitational forces -- can escape to other dimensions. Dvali says this would cause "leaks" in gravity over cosmic proportions, reducing gravitational pull at larger distances more than expected. "The gravitons behave like sound in a metal sheet," says Dvali. "Hitting the sheet with a hammer creates a sound wave that travels along its surface. But the sound propagation is not exactly two-dimensional as part of the energy is lost into the surrounding air. Near the hammer, the loss of energy is small, but further away, it's more significant." The effect is to alter the space-time continuum, speeding up universal expansion. "Virtual gravitons exploit every possible route between the objects," Dvali said, "and the leakage opens up a huge number of multi-dimensional detours, which brings about a change in the law of gravity." The speeding up of the universe suggest that Einstein’s laws of General Relativity, describing the interaction of space and matter, must be modified at large cosmic distances. "It is this modification, and not dark energy, that is responsible for the accelerated expansion of the universe," Dvali concludes. The idea might be testable. Gravity leakage should create minor deviations in the motion of planets and moons. Astronauts on the Apollo 11 mission installed mirrors on the lunar surface. By shooting lasers at the mirrors, a reflected beam can be monitored from Earth to measure tiny orbital fluctuations. Dvali said deviations in the Moon's path around Earth might reveal whether gravity is really leaking away. http://www.space.com/scienceastronomy/dark_energy_050228.html
Life waxes and wanes with bobbing of the Solar System (Moderator)	posted 4/4/06 2:09 PM     Life waxes and wanes with bobbing of the Solar System 17:24 30 March 2006 NewScientist.com news service Maggie McKee The solar system's up-and-down motion across our galaxy's disc periodically exposes it to higher doses of dangerous cosmic rays, new calculations suggest. The effect could explain a mysterious dip in the Earth's biodiversity every 62 million years. The solar system moves through the Milky Way rather like a child on a merry-go-round. It completes a circuit of the galaxy once every 100 million years or so but as it goes it bobs up and down through the dense galactic disc. Previous research had suggested this motion might affect Earth's climate as the solar system passes through the giant hydrogen clouds concentrated in the galaxy's spiral arms. Some researchers have said these clouds could be dense enough to sprinkle the Earth's atmosphere with dust, blocking out sunlight and cooling the planet. Others have suggested the gravitational pull of the clouds may dislodge comets from their spherical halo surrounding the solar system and send them crashing into the Earth, causing major extinctions. Compressed wind Still other researchers have pointed out that the clouds could compress the solar wind, which shields the solar system from energetic cosmic rays from the galaxy. These cosmic rays - charged particles accelerated to high energies by supernova explosions - could then leak into the Earth's atmosphere. There they could spur the formation of clouds - cooling the planet - and destroy the ozone layer, killing off species by allowing harmful ultraviolet light to reach the Earth's surface. However, the solar system takes a few hundred thousand years to pass through one of these giant clouds, and the fossil record does not show regular dips in biodiversity on this timescale, say Mikhail Medvedev and Adrian Melott of the University of Kansas in Lawrence, US. Instead, Medvedev cites a 2005 Nature study showing the number of species has dropped about every 62 million years for at least the past 542 million years. This timescale coincides with the 64 million years it takes for the solar system to move vertically through the disc of the galaxy and back again, he says. Medvedev presented research linking the two effects at an astrobiology conference in Washington DC in the US this week. Most of Earth's biggest extinctions occurred when the solar system was at its most northerly point in its cycle, which stretches about 230 light years above the galactic plane. Medvedev says that more cosmic rays enter the Earth's atmosphere at that point, killing off species. Cosmic shield He says the effect is similar to the compression of the solar system's protective solar wind when it passes through a giant hydrogen cloud. The Milky Way's stars produce a wind of charged particles whose magnetic fields deflect incoming cosmic rays from beyond the galaxy. But the entire Milky Way is moving due north at 200 kilometres per second towards a giant grouping of galaxies called the Virgo Cluster. This movement compresses the galactic wind on the galaxy's north side, allowing in higher levels of potentially life-harming extragalactic cosmic rays, says Medvedev. "When the Sun is moving up through the galactic plane, the cosmic ray flux is increasing, and when it goes down through the plane, it's decreasing," he told the conference. He said the periods of high extragalactic cosmic ray influxes match observed lows in biodiversity so well that the alignment has just a one in 10 million chance of being a coincidence. Habitable zones "I think it's very convincing," says Paul Davies, an astrobiologist at Macquarie University in Sydney, Australia. He says the research could shed light on "habitable" zones where life could most easily take hold. These zones are found in the solar system where liquid water can persist, and in the Milky Way between the galactic centre - where radiation levels are dangerously high - and the galaxy's outskirts, which have a dearth of the heavy elements necessary for life. "Then the question is: is there an intergalactic habitable zone?" he asks. He says the possibility that there are "sides of the galaxy where the cosmic ray flux could be high" suggests there is such a region between galaxies where the flux is low. http://www.newscientist.com/article/dn8923--life-waxes-and-wanes-with-bobbing-of-the-solar-system.html

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