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.
advertisement
