Документ взят из кэша поисковой машины. Адрес
оригинального документа
: http://star.arm.ac.uk/nibulletin/2006/Jan-8.html
Дата изменения: Mon Jan 9 12:50:06 2006 Дата индексирования: Tue Oct 2 03:32:32 2012 Кодировка: Поисковые слова: п п п п п п п п |
From: TerryMoselaol.com Date: Sun, 8 Jan 2006 11:26:45 EST Subject: NY Party, Stardust, Amateurs & Neutrinos, IFAS Ast of the Year. Hi all, 1. Congrats to all who contributed to another excellent IAA NY party! In particular, the 'Michelin Star' catering by IAA member Derwen Campbell, which was just mouthwateringly delicious, not to mention copious! Also to George Brannan for most of the arrangements & the quiz, Philip Baxter for the quiz prizes, John Hall for the financial aspect, & Danny Collins for help with the drinks. And my hot punch seemed more popular than ever, with some coming back for not just seconds and thirds, but at least one fourth! It was so good that we even forgave John O'Neill, John Flannery & Gerry Moloney from Dublin, Rush (obviously not well named!) & Kells, for arriving almost an hour late! 2. STARDUST (the other one!). The only space mission named after an astronomy club magazine, "STARDUST", will return to Earth on 15 January, with a sample of comet dust, and a planned touchdown in Utah. Just before 3 a.m. MST, the spacecraft will jettison its return capsule, which will plunge into Earth's atmosphere at nearly 29,000 miles per hour, the greatest return speed ever recorded. A few moments later, after the capsule slows to just faster than the speed of sound, a parachute will apply the brakes and Stardust will settle to the ground on the Air Force's Utah Testing and Training Range southwest of Salt Lake City. The return capsule contains tiny bits of dust captured two years ago as it spewed from a comet called Wild 2. The tennis-racquet-shaped collector used a remarkably light and porous material called aerogel to capture the particles, each much smaller than a grain of sand and traveling six times the speed of a bullet fired from a rifle. Earlier, the reverse side of the collector snared interstellar dust grains flowing into the solar system from other stars in our galaxy. In all, the capsule contains tens of thousands of comet grains and about 100 bits of interstellar dust. "It's really quite an epic thing. I think it tends to get overlooked because it's just a little mission, and there aren't any people on board," said D. Brownlee, University of Washington, Pricipal Investigator. "But the really big part of the research is just getting ready to start, when the material goes to the laboratory. The train is headed for the station and we're all waiting for it." Stardust is part of NASA's series of Discovery missions and is managed by the Jet Propulsion Laboratory in Pasadena, Calif. Besides the UW, other collaborators are Lockheed Martin Space Systems; The Boeing Co.; Germany's Max-Planck Institute for Extraterrestrial Physics; NASA's Ames Research Center; and the University of Chicago. After the capsule touches down in the Utah desert, a canister bearing the aerogel collector grid will be removed and taken to the Johnson Space Center in Houston, where the samples will be cataloged and sent to scientists around the world. Brownlee expects them to provide key information on the formation of the solar system 4.6 billion years ago and possibly to shed light on the origins of life on Earth. Scientists are likely to study Stardust's treasure for decades to come. Stardust was launched on Feb. 7, 1999, and set off on three giant loops around the sun. It began collecting interstellar dust in 2000 and met Wild 2 (pronounced Vilt 2) on Jan. 2, 2004, when the spacecraft weathered a hailstorm of comet particles and snapped exceptional close-up photographs of the comet's surface. During its 2.88 billion-mile voyage Stardust made one pass by Earth to get a speed boost from the planet's gravity, and later staged a dress-rehearsal for the comet encounter when it maneuvered very close to Asteroid 5535 Annefrank. The tensest moment other than the comet encounter came in November 2000, while the spacecraft was cruising along some 130 million miles from the sun. A huge solar flare, 100,000 times more energetic than usual, engulfed Stardust and its special digital cameras that help the spacecraft know where it is by viewing the stars and making comparisons with a comprehensive star chart stored in the onboard computer. The high-energy solar flare electrified pixels in the cameras, producing dots that the computer interpreted as stars. Suddenly th e spacecraft did not know where it was and, in a preprogrammed act of self-preservation, it turned its solar panels toward the sun, losing communication with Earth. Ground controllers finally found a faint signal and were able to contact Stardust and correct the problem. A little more than three years later the spacecraft finally met the target that scientists had been aiming for since 1974, when a close encounter with Jupiter altered Wild 2's orbit and brought it to the inner solar system. That made the mission feasible. Scientists have collected thousands of meteorites and cosmic dust particles on Earth, Brownlee noted, but with few exceptions the origin of those materials is unknown. Now there will be samples of material from another known body in space, and those grains can be compared with all the previously collected meteorites and bits of dust to see if there are similar origins. The Wild 2 samples are cryogenically preserved solar system building blocks, kept close to their original state because they have existed mostly at the outer edge of the solar system. "Virtually all the atoms in our bodies were in little grains like the ones we're bringing back from the comet, before the earth and sun were formed," Brownlee said. "Those grains carry elements like carbon, nitrogen and silicon from one place to another within our galaxy, and they helped form the sun, the planets and their moons." Stardust's photographs of Wild 2 also are cause for further study. Brownlee still marvels at the rugged surface the pictures disclosed, a surface very different from the smoother cores of the other three comets - Tempel 1, Borrelly and Halley - that have been photographed up close. "For unknown reasons, the surface of Wild 2 looks quite different - spectacularly different - from asteroids, moons, planets and even from other comets," he said. 3: AMATEUR ASTRONOMERS CAN HELP FIND NEUTRINOS: Ohio State University scientists have thought of a new way to solve an astronomical mystery, and their plan relies on a well-connected network of amateur stargazers and one very elusive subatomic particle. To understand what happens inside exploding stars, or supernovae, scientists need to study particles called neutrinos, explained John Beacom, assistant professor of physics and astronomy at Ohio State University. Neutrinos are formed in the nuclear reactions that make stars like our sun shine. Exploding stars overflow with the particles, and flood the universe with them. Neutrinos should be everywhere, but they are very hard to detect - so hard to detect, in fact, that even though countless neutrinos burrow through our planet every second, scientists only capture a few of them each day. Scientists know that most neutrinos they do detect probably come from our own sun, from nuclear reactors in terrestrial power plants, or from cosmic radiation interacting with our atmosphere. There has been no way to distinguish whether a particular neutrino came from elsewhere, until now. That's why Beacom and his team's discovery - that each year, one or two of the neutrinos detected on Earth can probably be matched to the exploding star that made them - represents a major step forward for supernova astrophysics. The discovery also comes at a special time, Beacom said. The method will fully exploit the capabilities of the next generation of neutrino detectors, which are now being planned, and take advantage of a growing number of amateur astronomers who are capable of discovering supernovae. For a study appearing in a recent issue of the journal Physical Review Letters, Beacom and his coauthors developed a kind of litmus test for finding supernova neutrinos: If a detector on Earth registers two of the particles within ten seconds, odds are high that they came from a supernova in a nearby galaxy. Alternatively, if an astronomer - amateur or otherwise - spots a supernova, scientists at neutrino detectors can look back through their records to see if they captured a neutrino around that time. Given that a few supernovae occur in nearby galaxies every year, and given the sensitivity of neutrino detectors on Earth, they've determined that at least one of those scenarios - the two-in-ten-seconds event or the identification of a supernova neutrino after the fact - should be able to happen about once a year. The professionals need amateur astronomers to help spot new supernovae fast, so scientists can quickly match captured neutrinos with the exploding stars that made them. "Even with all our modern telescopes, the professionals can't look at the whole sky at once," Beacom said. "But the amateurs are everywhere. With relatively small telescopes, they can see these nearby supernovae, which are very bright - often brighter than their host galaxies." Coauthor Hasan Yuksel, a postdoctoral researcher at Ohio State, explained that many of today's so-called amateur astronomers aren't really so amateur. "You can think of them more as 'professional amateurs,'" he said. These are the semi-pro players of the hobby set - skilled folks who build custom telescopes. They have day jobs, but they scan the skies at night, and share their findings with other amateurs over the Internet. Often, they have ties to professional astronomers. When a major discovery is made, they know as soon as the professionals do. Yuksel also pointed out that since 2002, there were at least nine supernovae identified in galaxies within about 30 million light years (180 trillion miles) of our Milky Way, and more than half of those were discovered by amateurs. Surprisingly, the Ohio State physicists got their idea in a "eureka" moment -- after a discussion with colleagues at the Department of Astronomy's morning coffee event. This daily review of new journal papers posted to an online archive (arXiv.org) has been going on since the 1990s, and often inspires faculty and students to pursue new lines of research. Walking back to their offices after coffee, Yuksel asked Beacom and visiting scholar Shin'ichiro Ando about a special class of galaxies called starburst galaxies, in which unusually high numbers of stars are being born. Wouldn't those galaxies also have large numbers of supernovae? Wouldn't nearby starburst galaxies be good places to look and find out? Beacom said that something clicked. "We realized that maybe it's not totally crazy to look for neutrinos from supernovae in nearby galaxies," he said. The three performed detailed calculations about supernova rates in nearby galaxies, and found that the explosions probably happen more often than people once thought - about three times a year. Then they looked at the rates at which neutrinos are caught in giant underground detectors on Earth. Their discovery came down to calculating the odds: it's highly unlikely that a neutrino detector on Earth would capture two particles within any 10 second interval unless both of those neutrinos came from a supernova - in fact, the same supernova. "We were kicking ourselves for not thinking of this before," Beacom said. He cited Supernova 1987A, which occurred in a galaxy that is a very close companion to the Milky Way. Because detectors on Earth captured 20 neutrinos in only a few seconds during that event, astronomers knew for sure that they came from 1987A. But since then? "A big fat zero," he said. "What if using this technique, we could have been identifying one additional supernova neutrino per year? By now, we would have collected a sample as big as that burst in 1987." With the much larger neutrino detectors that are now being devised, and with the large number of supernovae that are being spotted these days, it could be done. Galaxies up to 200 times farther away than the one that spawned Supernova 1987A are still considered near by astronomical standards, and amateurs would be able to spot supernovae in them. Those galaxies may give us only one or two neutrinos per year, but that's still more than scientists would be able to study otherwise. "These are somewhat desperate measures," Ando admitted. "Why are we so desperate? Since a supernova expends 99 percent of its energy in neutrinos, those neutrinos tell the story of how the explosion works, and therefore we have to find them." Supernova neutrinos are everywhere, but the vastness of space keeps them hidden. So, at least a thousand years after people first noticed supernovae in the skies, what's happening inside these exploding stars is still a mystery. When scientists simulate supernovae on computer, something always goes wrong. The explosion starts, and then it fizzles. "If we can't make a supernova blow up on the computer, that means we're missing something. We need clues. We need to find those neutrinos," Ando continued. Beacom envisions that scientists at neutrino detectors could sound an alarm whenever they detect two particles in ten seconds. Since supernovae emit neutrinos at the very start of the explosion, the particles would reach Earth hours before the supernovae would be visible in telescopes, and the announcement would amount to a supernova forecast. Alternatively, when astronomers spot a nearby supernova, they could ask the scientists at the detectors to look back through their data from previous hours to find any particle events. At Beacom's suggestion, scientists working at the Japanese neutrino detector Super-Kamiokande are going to search their records for events that could be linked to nearby supernovae in past years. "While this detector is smaller than those envisioned for the future, it's been in operation for a decade or two, so it actually stands a good chance of having detected the first neutrino from an identified supernova beyond the Milky Way and its closest companions," Beacom said. 4. IFAS Amateur Astronomer of the year: Congratulations to Martin McKenna of EAAS, from Maghera, County Derry, who is the IFAS Astronomer of the Year 2005 as voted by his peers. And he thoroughly deserves it for his tireless observing AND for sharing it on the IFAS boards. It reflects the time and effort he spends in comet hunting and deep sky observing. Martin has also recently started a nova patrol and has reported observing many atmopspheric phenomena including the Gegenshein and many lunar and solar haloes, upper tangential arcs and much more. His most recent observing includes seeing Asteriod Vesta with the unaided eye. And an honourable mention should go to his tireless companion - Conor, of the IAA, Co. Derry. Clear Skies, Terry Moseley
Last Revised: 2006 January 9th
WWW contact:webmaster@arm.ac.ukGo to HOME Page