Astronomers witness star's death, birth of new black hole

"I suspect it's much easier to make a very massive black hole if there is no supernova," said researcher Krzysztof Stanek.
By Brooks Hays   |   May 25, 2017 at 3:17 PM
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May 25 (UPI) -- In 2015, a star tracked by astronomers since 2009, suddenly disappeared. New research suggests the star collapsed and became a black hole, but avoided the explosive violence of a supernova.

The discovery, detailed in the Monthly Notices of the Royal Astronomical Society, could explain why many of the universe's most massive stars die without a parting explosion.

"The typical view is that a star can form a black hole only after it goes supernova," Christopher Kochanek, professor of astronomy at Ohio State University, said in a news release. "If a star can fall short of a supernova and still make a black hole, that would help to explain why we don't see supernovae from the most massive stars."

The star N6946-BH1 was one of several in the galaxy NGC 6946 being eyed by Kochanek and his colleagues. The so-called "Fireworks Galaxy" is well known for its plethora of supernova explosions.

When N6946-BH1 slowly brightened before disappearing -- without a final crescendo -- researchers began to investigate further. A series of observations by the Large Binocular Telescope, as well as NASA's Hubble and Spitzer space telescopes, confirmed the star had neither dimmed nor become obscured by dust clouds.

By process of elimination, researchers concluded the star had become a black hole.

"N6946-BH1 is the only likely failed supernova that we found in the first seven years of our survey," said researcher Scott Adams, a former Ohio State student. "During this period, six normal supernovae have occurred within the galaxies we've been monitoring, suggesting that 10 to 30 percent of massive stars die as failed supernovae."

"This is just the fraction that would explain the very problem that motivated us to start the survey, that is, that there are fewer observed supernovae than should be occurring if all massive stars die that way," Adams added.

The findings could explain how supermassive black holes are born. If the most massive stars exploded in a fiery death, they likely wouldn't have enough material leftover to form a black hole.

"I suspect it's much easier to make a very massive black hole if there is no supernova," said study co-author Krzysztof Stanek.

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