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Sounds near middle 'C' rock stars to death UNIVERSITY OF ARIZONA NEWS RELEASE Posted: February 12, 2006 Scientists have made the astonishing discovery that sound might drive supernovae explosions. Their computer simulations say that dying stars pulse at audible frequencies -- for instance, at about the F-note above middle C -- for a split second before they blow up. Researchers in the 1960s began using computer models to test ideas about what, exactly, causes stars to explode. But mathematical simulations have so far failed to satisfactorily explain the inner workings of nature's most spectacular blasts. Neutrinos -- subatomic particles widely thought to power supernovae explosions -- don't seem to be energetic enough to do the job, especially for more massive stars. More sophisticated models that include convective motion work a bit better, but not well enough. Adam Burrows of The University of Arizona and colleagues at UA's Steward Observatory, Hebrew University, and Germany's Max Planck Institute (Potsdam) have developed computer models that simulate the full second or more of star death, from the dynamics of core collapse through supernova explosion. Their two-dimensional computer models allow for the fact that supernovae outbursts are not spherical, symmetrical events. A supernova is a massive star that has burned for 10 million to 20 million years and developed a hot, dense 'white dwarf' star about the size of Earth at its core. When the white dwarf reaches a critical mass (about 1.5 times the mass of the sun), it collapses and creates a spherical shock wave, all within less than half a second before the star would explode as a supernova. However, in all the best recent simulations, the shock wave stalls. So theorists have focused their work on what might revive the shock wave into becoming a supernova explosion. According to Burrow's new results, part of the problem is that other computer models don't run long enough. His team's detailed models involve a million steps, or about five times as many as typical models that calculate only the first few hundred milliseconds of supernovae events. Burrows team's simulations also characterize the natural motion of a supernova core, something that other detailed models do not. "Our simulations show that the inner core starts to execute pulsations," Burrows said. "And they allow us to follow the development to explosion for a longer time than other models do. They show that after about 500 milliseconds, the inner core begins to vibrate wildly. And after 600, 700 or 800 milliseconds, this oscillation becomes so vigorous that it sends out sound waves. In these computer runs, it's these sound waves that actually cause the star to explode, not the neutrinos." He added, "We were quite sure when we started seeing this phenomenon that we were seeing sound waves, but it was so unexpected that we kept rechecking and retesting our results." The team has used their models to make billions of calculations on computer clusters in the UA astronomy department, at Berkeley's supercomputer center and elsewhere, checking their analysis for the past year. They are publishing the research in the Astrophysical Journal. Their research is funded by the National Science Foundation, the Department of Energy, and the Joint Institute for Nuclear Astrophysics. The team got a clear picture of what likely happens by making movies from their simulations. Burrows has posted the movies on his Website Collapsing material falls lopsidedly onto the inner core and soon excites oscillations at specific frequencies in the simulations. Within hundreds of milliseconds, the inner core vibrations become so intense that they actually generate sound waves. Typical sound frequencies are about 200 to 400 hertz, in the audible range bracketing middle C. "Sound also generates pressure, which pushes the exciting streams of infalling matter to the opposite side of the core, further driving the core oscillations in a runaway process," Burrows said. "The sound waves reinforce the shock wave (created by the collapsed star) until it finally explodes aspherically." Burrows said that others who study supernova explosions in computer experiments will be skeptical of his team's results -- and should be. "This is such a break from 40 years of traditional thinking that one should be cautious trumpeting it," he said. "Nevertheless, this is provocative and interesting. It would open up many new possibilities and perhaps solve a long-standing problem of what triggers supernovae explosions." |
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Seven months after the successful maiden voyage of space shuttle Columbia, astronauts Joe Engle and Richard Truly took the orbiter back into space on mission STS-2. The November 12, 1981 launch demonstrated that the space shuttle was the world's first reusable manned spacecraft. Although their mission would be cut short, Engle and Truly performed the first tests of the shuttle's Canadian-made robotic arm. The crew tells the story of the mission in this post-flight presentation.
The space shuttle era was born on April 12, 1981 when astronauts John Young and Bob Crippen rode Columbia into Earth orbit from Kennedy Space Center's launch pad 39A. The two-day flight proved the shuttle could get into space as a rocket and return safely with a runway landing. Following the voyage of STS-1, the two astronauts narrated this film of the mission highlights and told some of their personal thoughts on the flight.
NASA Administrator Mike Griffin, along with his science, spaceflight, exploration and aeronautics chiefs, hold this news conference in Washington on February 6 to discuss the agency's proposed budget for Fiscal Year 2007. The budget would give NASA a slight increase in funding over 2006, but it features cuts in some projects to pay for funding shortfalls in the shuttle program. 
The Expedition 12 crew tosses overboard an old Russian spacesuit loaded with ham radio gear during a spacewalk outside the International Space Station. The eery view of the lifeless suit tumbling into the darkness of space was captured by station cameras.
The flight of shuttle Discovery in October 1998 captured the public's attention with the triumphant return to space by John Glenn. The legendary astronaut became the first American to orbit the Earth some 36 years earlier. His 9-day shuttle mission focused on science experiments about aging. This post-flight presentation of highlights from the STS-95 mission is narrated by the astronauts.
Space shuttle Atlantis and a multinational crew flew to the Russian space station Mir in June 1995 for the first in a series of joint docking missions, launching a new era of cooperation in space between the United States and Russia that would pave the way for the International Space Station. This post-flight presentation of highlights from the historic STS-71 mission is narrated by the astronauts.
On the 20th anniversary of the space shuttle Challenger tragedy, a memorial service was held at the Kennedy Space Center's Space Mirror. Speakers at the tribute to honor the lost Challenger, Columbia and Apollo 1 astronauts included the widow and son of Challenger commander Francis "Dick" Scobee, officials with the Astronauts Memorial Foundation, two local U.S. Representatives, commander of the first shuttle flight after Challenger and the Kennedy Space Center director.
The New Horizons spacecraft begins a voyage across the solar system to explore Pluto and beyond with its successful launch January 19 aboard a Lockheed Martin Atlas 5 rocket from Cape Canaveral, Florida.