For the first time, astronomers have witnessed a star disappear right before their eyes. Known as N6946-BH1, the star appears to have collapsed into a black hole without the usual flair of a supernova, which not only marks the first time scientists have witnessed the birth of a black hole, but could change our understanding of the life and death of stars.

According to conventional thinking, when a star exhausts its energy supply, it violently ejects most of its matter outwards in a supernova, before collapsing in on itself to form a black hole. But N6946-BH1 has bucked the trend, skipping the supernova stage and quietly collapsing into a black hole. These failed supernovae (or “massive fails”, as the team calls them) could help patch some holes in our stellar knowledge.

“The typical view is that a star can form a black hole only after it goes supernova,” says Christopher Kochanek, lead researcher on the study. “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.”

Some 22 million light-years from Earth, the star N6946-BH1 is located in (or used to be, anyway) the galaxy NGC 6946, which is often known as the Fireworks Galaxy due to how regularly its stars go supernova. But this one was different. Telescope images show that N6946-BH1 was clearly visible in 2007, brightened slightly around 2009, and had vanished completely by 2015.

To confirm that a dust cloud or something similar hadn’t just obscured their view, the astronomers examined the spot in the visible light spectrum with the Hubble Space Telescope, and in infrared with Spitzer, and came up empty in both cases. N6946-BH1 was simply gone.

With a mass 25 times that of the Sun, the resulting supernova should have been clearly visible. Instead, that minor brightening may have been a failed supernova, which would be the first time one has been directly detected. If stars can collapse in this way, the team says, it could help explain why supernovae from particularly massive stars are rarely spotted.

“N6946-BH1 is the only likely failed supernova that we found in the first seven years of our survey,” says Scott Adams, co-author of the study. “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.”

The research was published in the Monthly Notices of the Royal Astronomical Society, and the team discusses the find in the video.

Source: Ohio State University

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