Our models for how stellar black holes form are just that, models. They're based on the complicated mathematics of what happens when a massive star collapses at the end of its lifecycle. But scientists haven't actually witnessed the process of black hole formation directly before. That is, until now.
Using data from the Hubble Space Telescope, a team of astronomers from Ohio State University in Columbus believe they have been observing a red supergiant star, N6946-BH1, at the end of its lifecycle. In fact, in their latest observation, the star appears to have poofed out of existence. Where recently there was a bright star, now there only remains a darkness with a faint afterglow, reports New Scientist.
“This may be the first direct clue to how the collapse of a star can lead to the formation of a black hole,” said Avi Loeb at Harvard University.
The star, which is about 20 million light-years away, was first observed in 2004. Back then it was a star about 25 times larger than our sun. Later, in 2009, astronomers were witness to a spectacular light show as N6946-BH1 suddenly flared to become a million times brighter than our sun, and then faded just as suddenly. It was as if a bomb had exploded within its core.
Researchers now believe this bright explosion was an example of what models predict about the final moments before a star collapses into a black hole, as a cloud of hydrogen ions left over from when the dying star ignites.
The newest Hubble images of this star seem to confirm that it has indeed collapsed into a black hole. They show ... well, they show almost nothing. Where there was once a bright star, now there's only darkness. Though the star has vanished from the visible spectrum of light, there remains a faint hint of its previous existence: a pale infrared afterglow.
Of course, the star didn't just disappear. It transformed into a black hole. Or at least, that's the best guess. Scientists can't be certain of what's happened until they make more measurements. For instance, when material falls into a black hole, it emits X-rays in a particular spectrum. Spotting these X-rays will be the next step to confirming the existence of a new black hole.
The team will get an opportunity to make these observations in just a few months, when new data from the Chandra X-ray Observatory becomes available.
If it turns out that N6946-BH1 has, as suspected, collapsed into a black hole before our eyes, it will be the first time such an event has ever been directly observed in real time. This could not just confirm our models and simulations about how stellar black holes form, but it could help us to improve them.
It's pretty remarkable, though, that an event like this could be predicted and simulated decades before anyone had ever observed it happening in reality.