INVISIBLE black hole! Hubble Space Telescope does a first, finds what has never been seen

tech.hindustantimes.com:

Astronomers famously snapped the first ever direct image of a black hole in 2019, thanks to material glowing in its presence. But many black holes are actually near impossible to detect. Now another team using the NASA Hubble Space Telescope seems to have finally found something nobody has seen before: a black hole which is completely invisible. The research, which has been posted online and submitted for publication in the Astrophysical Journal, is yet to be peer-reviewed.

Black holes are what’s left after large stars die and their cores collapse. They are incredibly dense, with gravity so strong that nothing can move fast enough to escape them, including light. Astronomers are keen to study black holes because they can tell us a lot about the ways that stars die. By measuring the masses of black holes, we can learn about what was going on in stars’ final moments, when their cores were collapsing and their outer layers were being expelled.

It may seem that black holes are by definition invisible – they after all earned their name through their ability to trap light. But we can still detect them through the way they interact with other objects thanks to their strong gravity. Hundreds of small black holes have been detected by the way they interact with other stars.

There are two different approaches to such detection. In “X-ray binary stars” – in which a star and a black hole orbit a shared centre while producing X-rays – a black hole’s gravitational field can pull material from its companion. The material circles the black hole, heating up by friction as it does so. The hot material glows brightly in X-ray light, making the black hole visible, before being sucked into the black hole and disappearing. You can also detect