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Hubble says Earth safe from some gamma-ray bursts NASA NEWS RELEASE Posted: May 10, 2006 Homeowners may have to worry about floods, hurricanes, and tornadoes destroying their homes, but at least they can remove long-duration gamma-ray bursts (GRBs) from their list of potential natural disasters, according to recent findings by NASA's Hubble Space Telescope.
Now astronomers analyzing long-duration bursts — those lasting more than one to two seconds — in several Hubble telescope surveys have concluded that the Milky Way Galaxy is an unlikely place for them to pop off. They find that blasts tend to occur in small irregular galaxies where stars are deficient in heavier elements like carbon and oxygen. The Milky Way's starry population, by contrast, is rich in heavier elements. Suspecting that knowledge of their environments might help determine what types of stars produce gamma-ray bursts, the astronomers, led by Andrew Fruchter of the Space Telescope Science Institute in Baltimore, Md., used Hubble to examine the environments of 42 long-duration bursts and 16 supernovae. They found that the small fraction of supernovae that produce the bursts live in a very different environment from the average supernova. Fruchter's results appear in the May 10 online edition of the journal Nature. Fruchter's team found that most of the long bursts in the sample were detected in small, faint, misshapen, (irregular) galaxies, which are usually deficient in heavier elements. Only one of the bursts was spotted in a spiral galaxy like our Milky Way, suggesting that our galaxy is an unlikely host for long-duration bursts. By contrast, the hosts of supernovae were divided equally between spiral and irregular galaxies, those with greater or smaller concentrations of heavier elements. Fruchter's team also found that long bursts are far more concentrated in the brightest regions of their host galaxies where the most massive stars reside. Supernovae, on the other hand, occur throughout their host galaxies. "The discovery that long-duration gamma-ray bursts lie in the brightest regions of their host galaxies suggests that they come from the most massive stars 20 or more times as massive as our Sun," Fruchter said. "Their occurrence in small irregulars implies that only stars that lack heavy chemical elements tend to produce long-duration GRBs." This means that long bursts happened more often in the past when galaxies did not have a large supply of heavy elements. Galaxies build up a stockpile of heavier chemical elements through the ongoing evolution of successive generations of stars. Early-generation stars formed before heavier elements were abundant in the universe. Massive stars abundant in heavy elements are unlikely to trigger bursts because they may lose too much material through stellar "winds" off their surfaces before they collapse and explode. When this happens, the stars don't have enough mass left to produce the proper conditions that would trigger the phenomenon.
This means that extremely high-mass stars that puff away too much material may not be candidates for long bursts. Likewise, neither are stars that give up too little material. "It's a Goldilocks scenario," Fruchter said. "Only supernovae whose progenitor stars have lost some, but not too much, mass appear to be candidates for the formation of GRBs." Gamma-ray bursts can be divided into two classes: short bursts, which last between milliseconds and about two seconds, and produce very high-energy radiation, and long bursts, which last between two and tens of seconds, and create less energetic gamma rays. Although long bursts are unlikely to strike in galaxies like our Milky Way, short bursts could still happen. Short bursts are believed to arise from collisions between two compact objects, such as neutron stars. However, even with their higher-energy radiation, short bursts are typically 100 to 1,000 times less powerful overall than long bursts and would pose much less of a threat to life if one were to occur in our galaxy. |
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Space shuttle Challenger was transformed into an orbiting observatory to study the sun, stars and space environment during the Spacelab 2 mission in the summer of 1985. But getting into space wasn't easy. The shuttle suffered an engine shutdown on the launch pad, then during ascent two weeks later lost one of its three main engines. It marked the first Abort To Orbit in shuttle history. In this post-flight film, the crew of STS-51F narrates highlights of the mission that includes tests using a small plasma-monitoring satellite was launched from Challenger's robot arm.
A seven-person crew featuring payload specialists from France and Saudi Arabia flew aboard the June 1985 mission of space shuttle Discovery. They narrate the highlights of STS-51G in this post-flight film. Three communications satellites -- for Mexico, the Arab countries and the U.S. -- were launched from the payload bay. And the SPARTAN 1 astrophysics spacecraft was deployed from the shuttle's robot arm for a two-day freeflight to make its science observations before being retrieved and returned to Earth.
The flight of Spacelab 3 aboard Challenger in April/May 1985 was a week-long scientific research mission using a laboratory tucked in the shuttle's payload bay. Experiments focused on material and fluid behaviors in weightlessness, plus observations of monkeys in the lab. The crew also watched amazing auroral displays over Earth. This post-flight crew film shows the highlights of STS-51B and includes remarkable views out the shuttle cockpit window during launch showing the Chesapeake Bay, New York City and Cape Cod as Challenger soared up the eastern seaboard.
Discovery launched April 12, 1985 on the STS-51D mission. A U.S. military communications satellite, known as Leasat 3, failed to activate after its deployment from the payload bay. That set the stage for a spacewalk -- the shuttle program's first unplanned EVA -- to attach handcrafted "Flyswatter" objects on the shuttle robotic arm to hit a timing switch on the satellite. The rescue attempt did not succeed. Upon landing at Kennedy Space Center, Discovery blew a tire. The crew, including Senator Jake Garn of Utah, narrate this post-flight film of highlights from the week-long mission.
NASA managers hold this news conference April 28 to give an update on plans for the next space shuttle mission, the ongoing external fuel tank testing and debates over further modifications.
The Boeing Delta 2 rocket carrying the CALIPSO and CloudSat atmospheric research spacecraft lifts off at 3:02 a.m. local time April 28 from Vandenberg Air Force Base, California.
Inside the Vehicle Assembly Building, the external fuel tank for the STS-121 space shuttle mission is hoisted into position for attachment with the twin solid rocket boosters atop a mobile launch platform. The tank, ET-119, will carry the liquid oxygen and liquid hydrogen to feed Discovery's three main engines during launch.
In preparation for space shuttle Discovery's departure from its Orbiter Processing Facility hangar for rollover to the Vehicle Assembly Building and mating with the tank and boosters, the ship's 60-foot long payload bay doors are swung shut.
