2006年VOA标准英语-Astronomers Find Signs Planets Might Form（在线收听）

By David McAlary
Washington
05 April 2006

New evidence from an orbiting U.S. telescope indicates that planets might rise up out of a dead star's ashes. This is the first time scientists have detected planet-building materials around a star that died in a fiery blast.

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Legend tells of a mythical bird that periodically burned itself to death and emerged from the ashes as a new phoenix. Astronomers have found evidence that planets might do something similar.

Artist's concept of stellar rubble  
  

The U.S. space agency's Spitzer Space Telescope surveyed the scene around a type of exploded star called a neutron star. It found a surrounding disk made up of debris shot out during the star's final death throes. Astrophysicist Deepto Chakrabarty of the Massachusetts Institute of Technology says the dusty rubble in this disk might ultimately stick together to form planets.

"Now, a remarkable thing about this disk is that it looks very much like a debris disk seen around young stars, and astronomers already know that planets can form from such disks. So it it possible by analogy that planets could also be forming in this very different, harsh environment around an old, dead star, a sort of birth after death, or renaissance," he said.

The neutron star that the Spitzer telescope observed is in the constellation Cassiopeia, 13,000 light years away, the distance it takes light to travel in that length of time. It was once a larger, bright star about 10 to 20 times more massive than our sun. The U.S. space agency says it probably collapsed under its own weight in its death throes about 100,000 years ago and blasted apart in an explosion astronomers call a supernova.

Spitzer's heat seeking infrared eyes were able to detect the warm glow of the dusty disk surrounding the burnt-out star, which is so dense after its collapse that a spoonful would weigh about two billion tons.

Until now, no one had ever seen such a disk around a dead star, but NASA astronomer Charles Beichman says scientists have been suggesting their possible presence since 1992, when the first planet discovered outside our solar system was detected around a neutron star.

"We think that the disk formed after the supernova explosion. Much of the material exploded into free space, but some of it just wouldn't have enough energy to escape the gravitational pull of the neutron star that was left. It would fall back down and probably was rotating so it formed into a disk-like structure, and that is what we are seeing in the Spitzer data," he said.

Beichman says the finding is another hint that planet formation is a very robust process that could happen in a wide variety of environments.

"We would like to understand the breadth of planet formation processes to understand better how our own planetary system was formed," he said.

This discovery is reported in the April 6 edition of the journal Nature.