Litterbugs of the Universe Busted

Dave Mosher

Date: 20 December 2007 Time: 08:02 AM ET

Dust littered the early universe and seeded the formation of rocky planets such as the Earth. But where, exactly, most of the celestial grit came from was uncertain until now.

Astronomers have found 10,000 Earth masses worth of dust surrounding Cassiopeia A, the remnants of a supernova about 11,000 light-years away from our planet. The NASA Spitzer Space Telescope observations show silicates, carbon, iron oxide, aluminum oxide and other dust-forming chemicals around the blown-out star.

Jeonghee Rho, an astronomer at the Caltech in Pasadena, Calif., thinks the discovery signals the first strong evidence that massive exploding stars really are the litterbugs of the universe.

"Now we can say unambiguously that dust — and lots of it — was formed in the ejecta of the Cassiopeia A explosion," Rho said. She and her team will detail their findings in the Jan. 20 issue of the Astrophysical Journal.

Stars like the sun are thought to burn too long to seed the cosmos with enough grit, and massive stars are probably too gassy and short-lived, the thinking goes. Cassiopeia A's explosion is extremely recent — the light reached Earth just 325 years ago — but Rho and her team think cosmic dust balls similar to the remnant began producing the stuff of terrestrial planets billions of years ago.

Within Cassiopeia A, the astronomers found cool yet freshly-made dust mixed in with jettisons of gas called "unshocked ejecta" deep inside the supernova leftovers.

"Dust forms a few to several hundred days after these energetic explosions, when the temperature of gas in the ejecta cools down," said team member Takashi Kozasa, an astronomer at Hokkaido University in Japan.

This activity had never been seen before and hints that supernovae can crank out plenty of dust to lead to planet formation, though it doesn't account for all of the universe's grit.

"Perhaps at least some of the unexplained portion is much colder dust, which could be observed with upcoming telescopes, such as Herschel," said team member Haley Gomez, an astronomer at the University of Wales in the UK.

Set to launch in 2008, scientists hope to use the European Space Agency's Herschel spacecraft to find such cold dust near quasars, thought to be hyperactive black holes, which X-ray observations suggest could produce the stuff.