Three years after shredding and absorbing a small star, a black hole has begun ‘burping’ energy from its astronomical meal.
Black holes pull apart the material of stars that drift too close to them in a process called ‘spaghettification’. These ‘tidal disruption events’ happen because the strong gravitational influence of a black hole pulls a star in one direction while squashing it in another direction.
One such event, named AT2018hyz by researchers, occurred in October 2018. When astronomers used powerful radio telescopes to check on the black hole responsible, they found it had begun emitting energy from the star it had swallowed – three years after devouring it.
“This caught us completely by surprise – no one has ever seen anything like this before,” said Yvette Cendes, an astrophysicist at the Harvard and Smithsonian Center for Astrophysics and lead author of a paper on the discovery.
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DESY, Science Communication Lab/Supplied
This illustration shows the “spaghettification” of a star by a black hole.
While it’s common for black holes to emit energy after a tidal disruption event, the paper says it is unusual for this to start happening years after the event.
“This is the first time that we have witnessed such a long delay between the feeding and the outflow,” said Edo Berger, professor of astronomy at Harvard University and a co-author of the paper.
”The next step is to explore whether this actually happens more regularly and we have simply not been looking at [tidal disruption events] late enough in their evolution.”
The finding is also strange because of the speed that the black hole is ejecting material. The outflows of most tidal disruption events travel at about 10% of the speed of light – but these “burps” are moving much faster at half of the speed of light, according to the paper.
Black holes are extremely dense, with a gravitational influence so strong that not even light can escape them.
According to the European Space Agency, black holes are likely at the centre of most galaxies – including our own.
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