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Small black hole found nearby

By David, 29 April 2021 News

Egg shaped star with black hole behind.

The gravity from a black hole is stretching a nearby star
Image: Lauren Fanfer, Ohio State

Black holes have such strong gravity that nothing, not even light can escape its clutches. We like to imagine that they are far away, like the supermassive black hole in the heart of our galaxy. But there may be black holes much closer to home. We’re just not very good at seeing them – after all, they’re black! But scientists think they might have found a small black hole only 1,500 light years away.

A strange red star

Meet V723 Monocerotis. It’s a red giant star with a secret. Scientists already knew it was orbiting something, and it got brighter and dimmer twice per orbit. Initially, they thought that V723’s had a partner star that was getting in the way. This is known as an eclipsing binary.

This explanation seemed a bit strange to astronomer Tharindu Jayasinghe. He was on the lookout for small black holes and thought V723 might be hiding one.

Tharindu and the team looked at how V723 got brighter and dimmer over time. It wasn’t sudden like you’d expect if something was getting in the way. It was much more gradual. It seemed that the star wasn’t completely round, but more rugby ball shaped.

Black hole buddy

It would take some powerful gravity to stretch an entire star. The researchers did some calculations about V723’s sneaky companion, and realised it was probably a black hole. So what else do we know about it?

This is one of the smallest black holes ever found, weighing in at only 3 times the mass of our Sun. As a comparison, the supermassive black hole at the centre of our galaxy has a mass 4 million times that of the Sun!

It’s possible that the dark companion to V723 is actually 2 neutron stars, or a neutron star and a white dwarf star. But a black hole is the simplest explanation.

While close for a black hole, this dark companion is a long way from Earth. It would take many lifetimes to travel 1,500 light years to reach it, even in a superfast spaceship. But researchers only spotted this black hole because of its partner star. There could be similar black holes lurking much nearer to Earth, invisible against the blackness of space.

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