July 21, 2005
Dust-enshrouded Star Looks Similar to Our Sun
Astronomers report tremendous quantities of warm dusty debris surrounding a star with luminosity and mass similar to the sun's, but located 300 light-years from Earth. The extraordinary nature of the dust indicates a violent history of cosmic collisions between asteroids and comets, or perhaps even between planets. The discovery is published July 21 in Nature.
"What is so amazing is that the amount of dust around this star is approximately 1 million times greater than the dust around the sun," said Eric Becklin, a UCLA professor of physics and astronomy, member of NASA's Astrobiology Institute, and co-author of the Nature paper. "It's likely there was a cosmic catastrophe, and a time of heavy bombardment, where large asteroids collided in the last few thousand years or less. It's incredible what must be going on."
Unlike hundreds of other stars with dust, where the dust is far from the star -- equivalent to beyond the orbit of Pluto -- this dust is orbiting in close to the star, where Earth-like planets are most likely to be, said Inseok Song, a former UCLA research scientist who is now an astronomer with the Gemini Observatory in Hawaii, and lead author of the paper.
Was Song surprised to see so much dust so near to the star, which is known as BD+20 307, and is in the constellation Aries?
"Definitely," he said. "I expected to find a much weaker excess because dust close to the star can't survive long."
"The amount of warm dust near BD+20 307 is so unprecedented I wouldn't be surprised if it was the result of a massive collision between planet-size objects, for example, a collision like the one which many scientists believe formed Earth's moon," said Benjamin Zuckerman, UCLA professor of physics and astronomy, member of NASA's Astrobiology Institute, and a co author of the paper. "According to this model, the early Earth was struck by a Mars-size object that generated an immense fountain of hot magma, some of which condensed to form the moon. But if even a small percentage of this magma escaped into orbit around the sun, it could have led to a condition such as we now witness at BD+20 307."
"This looks similar to our own solar system, and may well lead to a greater understanding of how our solar system formed," said Becklin, who is chief scientist for NASA's Stratospheric Observatory for Infrared Astronomy project. "It is very likely there are planets orbiting this star."
The team of astronomers used the 10-meter Keck I and the Gemini North telescopes on Mauna Kea in Hawaii to measure the heat radiation coming from the dust.
Very young stars, 10 million years old or younger, may have this much dust around them, but the evidence presented in Nature points to an age of at least a few hundred million years for BD+20 307. For stars that are hundreds of million years old, "this is the dustiest star, far and away," Zuckerman said. Typically, small dust particles get pushed away by radiation or wind, and larger dust particles often get destroyed in collisions or clump together to form larger objects.
"For 98 percent of the stars that have dust around them that have been found, the dust is far beyond the terrestrial planet region and wouldn't tell us anything about Earth," Zuckerman said. "Not more than 1 percent of stars of this age exhibit this kind of warm dust close to the star; the dust is radiating at about room temperature."
"The dust we see is similar in composition to dust in the solar system, but has been pulverized into tiny particles," said Alycia Weinberger, a former UCLA postdoctoral scholar who is now with the Carnegie Institution of Washington. "The Earth may have received lots of similar material in its first 600 million years, during a time when the inner solar system was bombarded by asteroids, comets and other debris."
"There are very few systems like this one that any astronomer has seen, just a tiny handful; you can count the examples on one hand," Zuckerman said. "My interpretation is that our solar system may be quite unusual. I expect this star to be studied over and over again. Many stars closer to Earth with an age comparable to that of our solar system during the era of heavy bombardment have been studied carefully and do not show this pattern."
"Since the early '80s," Song said, "many astronomers have eagerly searched for an analogy to our solar system's asteroidal belt at other stars. Our finding is a bona fide example of dust at the exo-asteroidal zone and it is chilling to see dust at the Earth-sun separation around a young solar analog -- like seeing our own sun back in time."
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