Collapsing star mysteriously reborn as black hole, reveal NASA's Hubble and Spitzer images

Image credits: NASA’s Goddard Space Flight Center/Katrina Jackson

New Delhi: A team of astronomers claimed that a massive, dying star may have been reborn as a black hole.

The observation was made using images from the Large Binocular Telescope (LBT), and NASA's Hubble and Spitzer space telescopes.

As the astronomers looked for remnants of the vanquished star, they found that it disappeared out of sight with a whimper instead of a bang.

“Massive fails” like this one in a nearby galaxy could explain why astronomers rarely see supernovae from the most massive stars, said Christopher Kochanek, professor of astronomy at The Ohio State University and the Ohio Eminent Scholar in Observational Cosmology.

NASA says the star, which was 25 times as massive as our sun, should have exploded in a very bright supernova. Instead, it fizzled out - and then left behind a black hole.

As many as 30 percent of such stars, it seems, may quietly collapse into black holes - no supernova required.

"The typical view is that a star can form a black hole only after it goes supernova," Kochanek explained. "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."

NGC 6946, a spiral galaxy 22 million light-years away that is nicknamed the 'Fireworks Galaxy' because supernovae frequently happen there - SN 2017eaw, discovered on May 14th, is shining near maximum brightness now - is among the galaxies the team led by Kochanek has been watching.

Starting in 2009, one particular star, named N6946-BH1, began to brighten weakly. By 2015, it appeared to have winked out of existence, says the NASA release.

After the LBT survey for failed supernovas turned up the star, astronomers aimed the Hubble and Spitzer space telescopes to see if it was still there but merely dimmed. They also used Spitzer to search for any infrared radiation emanating from the spot. That would have been a sign that the star was still present, but perhaps just hidden behind a dust cloud.

All the tests came up negative and the star no longer there. By a careful process of elimination, the researchers eventually concluded that the star must have become a black hole.

Scott Adams, a former Ohio State student who recently earned his doctorate doing this work, was able to make a preliminary estimate, although it's too early in the project to know for sure how often stars experience massive fails.

"N6946-BH1 is the only likely failed supernova that we found in the first seven years of our survey. 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," he said.

The findings have been published in the Monthly Notices of the Royal Astronomical Society.