Evrim Yazgin
Cosmos science journalist
Astronomers have seen a rare, extremely energetic explosion when stars at least 3 times bigger than the Sun wandered too close to a supermassive black hole.
The result was an unprecedented cosmic explosion. This type of event has been observed for the first time, leading to a new class of cosmic phenomena being named: “extreme nuclear transients”, or ENTs.
The findings are in an article published in Science Advances.
“We’ve observed stars getting ripped apart as tidal disruption events for over a decade, but these ENTs are different beasts, reaching brightnesses nearly 10 times more than what we typically see,” says first author Jason Hinkle from the University of Hawai‘i’s Institute for Astronomy (IfA).
“Not only are ENTs far brighter than normal tidal disruption events, but they remain luminous for years, far surpassing the energy output of even the brightest known supernova explosions.”
The most energetic ENT studied is Gaia18cdj. It emitted 25 times more energy than the most powerful supernova recorded. ENTs produce in 1 year the same amount of energy as 100 times our Sun’s energy output over its entire 10-billion-year lifetime.
Hinkle and colleagues spotted 2 unusual flares in data from the European Space Agency’s Gaia space observatory.
“When I saw these smooth, long-lived flares from the centres of distant galaxies, I knew we were looking at something unusual,” Hinkle says.
Over the next years, Hinkle’s team tried to figure out what these sources were using data from telescopes around the world.
They worked out that there was too much energy for a normal supernova explosion. This pointed the team to the flares being the result of accretion onto a supermassive black hole.
But normal black hole accretion usually shows irregular and unpredictable changes in brightness. The smooth, long-lasting flares of the ENTs suggests the gradual accretion of a massive star.
“ENTs provide a valuable new tool for studying massive black holes in distant galaxies,” says co-author Benjamin Shappee, also from the IfA. “Because they’re so bright, we can see them across vast cosmic distances – and in astronomy, looking far away means looking back in time.
“By observing these prolonged flares, we gain insights into black hole growth when the universe was half its current age, when galaxies were happening places – forming stars and feeding their supermassive black holes 10 times more vigorously than they do today.”
“These ENTs don’t just mark the dramatic end of a massive star’s life. They illuminate the processes responsible for growing the largest black holes in the universe,” Hinkle adds.
