Last year, astronomers spotted something strange in a galaxy far, far away – an extremely bright light, brighter than any supernova ever spotted before.
Yet that bright light, which astronomers named ASASSN-15lh, occurred where scientists say the conditions were wrong for such as massive supernova. Puzzled, they studied ASASSN-15 for months, finally determining that it was indeed not a supernova, but the death throes of an unfortunate star that had wandered into the path of a black hole.
"Our results indicate that the event was probably caused by a rapidly spinning supermassive black hole as it destroyed a low-mass star," said study lead author Giorgos Leloudas, reports the BBC.
ASASSN-15lh was discovered through the All-Sky Automated Survey for Supernovae (ASAS-SN). Supernovas occur when a loss of fuel or influx of new material causes the star to explode. Initially, astronomers believed that ASASSN-15lh was the most luminous supernova ever spotted.
This dazzling explosion took place 3.8 billion light years from the Earth and gave off 570 billion times more light than our sun – yet scientists say that the star that caused the explosion was unlikely to have been the source of a supernova, as it was not very massive.
"This gave the event the appearance of a very bright supernova explosion, even though the star would not have become a supernova on its own as it did not have enough mass," wrote astronomers at Queen’s University, Belfast, in a statement.
Yet the explosion occurred in a large, reddish galaxy, Space.com reports, where supernovae don’t typically happen because of an absence of massive young stars. The heat of the explosion’s aftermath, too, convinced astronomers that they might not be looking at a supernova – unlike supernovae, which cool over time, the remnants of this explosion heated up.
Instead of bearing all the hallmarks of a supernova, in fact, scientists say that the explosion looked more like a “tidal disruption” event, which laypeople know as a star death via black hole.
Black holes are known for their ability to swallow stars, although astronomers were at first confused by how this black hole would have caused such an explosion instead of simply gulping down the star whole.
"If you could take every person on earth and squeeze them on to a teaspoon – that would be the density of a neutron star, or neutron star material, and a black hole is probably 10 times denser than that,” said Queen’s University professor Stephen Smart on a BBC radio program.
"So it's an object from which light cannot escape, it's an object that is denser than any known matter that we can see or test in the universe."
Finally, scientists figured it out. Massive explosions such as ASASSN-15lh are rare, but can occur when a black hole shreds, or “spaghettifies” a star, ripping it apart and converting stellar material into brilliant light.
Astronomers credit modern technology with letting them observe this rare event.
“Years ago we just wouldn’t have been able to follow an event like this,” said paper co-author and UCSB professor Andy Howell, according to Forbes. “This study shows that large-area surveys, a global robotic telescope network and a NASA satellite can come together to reveal dramatic new discoveries that wouldn’t be possible without each piece of that puzzle.”