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Supernova is a dust factory

Grains of matter spewed by explosion offer clues to early star formation

GATHERING DUST  Observations of dust (red) detected in the center of the debris from Supernova 1987A suggest that such stellar explosions may be a source of cosmic dust. Visible light (green) and X-ray (blue) images show the expanding shockwave from the supernova.

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OXON HILL, Md. — The remnant of a recent supernova contains nearly a star’s mass of dust. The dust’s presence provides strong evidence that similar explosions distributed dust that seeded bursts of star formation billions of years ago.

For astronomers, dust is a bit different from the stuff on your dresser. Dust forms in space when searing-hot atoms of carbon, oxygen and silicon cool and clump together into solid grains as large as a thousandth of a centimeter across. These grains permeate the cosmos, serving as springboards for star formation and as surfaces on which other atoms combine into complex molecules, including the building blocks of life.

Lots of cosmic dust forms in the outer layers of old, bloated stars. Astronomers have strongly suspected that dust also forms after supernovas, the violent explosions of giant stars that send atoms hurtling through space at thousands of kilometers a second. In just a few years, dense clumps of material can cool from more than 700° Celsius to below –200°. But previous telescope surveys looking for a faint glow of cosmic dust grains in the aftermath of a supernova came up empty.

Remy Indebetouw, an astronomer at the University of Virginia in Charlottesville, and colleagues took another stab using a new high-resolution telescope network called the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. They pointed the telescopes at the remnant of a supernova about 168,000 light-years away in the constellation Dorado, whose light first arrived at Earth in 1987. Within the rapidly expanding shockwave from that explosion, the researchers detected the distinct spectral signature of dust-emitted radiation.

The supernova remnant’s grains collectively weigh in at about a quarter of the sun’s mass, Indebetouw reported January 6 at a meeting of the American Astronomical Society. “We found all this dust that had to have been made there,” he said.

This first definitive evidence of supernova-produced dust provides a clue to the makeup of the infant universe. Telescopes peering back in time to less than a billion years after the Big Bang have spotted individual galaxies with dust that weighs hundreds of millions of times as much as the sun. Supernovas seemed the logical candidate for supplying all that dust, but the unsuccessful telescope searches had thrown the idea into doubt. “We had wondered why we didn’t see the dust,” said Devin Silvia, an astrophysicist at Michigan State University in East Lansing. “That’s what makes this such a huge deal.”

Astronomers can’t officially call the mystery solved. Portions of the shockwave from the explosion have rebounded inward. When the shockwave reaches the newly created dust, much of it may vaporize. If that occurs, then it would suggest that supernovas in general may not be able to distribute the dust they create into their surroundings.

Silvia is optimistic, noting that most of the dust is in the form of large, robust grains. It will take more than 100 years for astronomers to determine the fate of the 1987 supernova’s dust, Indebetouw said. But Silvia added that ALMA may be able to probe older supernovas for comparison.

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