There is an area at the edge of black holes where matter can no longer remain in orbit and instead falls in, as predicted by Einstein in the Theory of General Relativity in 1915

https://m.stacker.news/31831
https://m.stacker.news/31832

For the first time, astronomers have observed the area right at the edge of a black hole, where matter stops orbiting and plunges straight down at close to the speed of light.

A team of astrophysicists from the University of Oxford, the University of Newcastle and the Institute of Astronomy, all in the UK, working with a colleague from the University of Virginia in the US, has found evidence to show that Albert Einstein was correct when his theory of General relativity predicted how matter that came close to a black hole would fall into it.

Previous research has shown that matter that gets too close to a black hole is torn apart due to the gravitational effect: atoms closer to the black hole are pulled with more force than those that are further away. The material then forms a ring around the black hole that we call an accretion disk.

Einstein's theory suggests that there should be a boundary between this accretion disk and the black hole. When the accretion disk crosses this boundary, it falls. Until now, it was not known whether the matter in the accretion disk falls gently or through a sudden dip. The theory of general relativity suggests that it should be the last option, but does not explain how it would be possible to observe it.

The research team was studying a binary system approximately 10,000 light-years away using the NuSTAR orbital X-ray telescope. Called MAXI J1820+070, the system has a black hole at its center, which has become its focus. To learn more about the black hole, they used data from the telescope to model its behavior.

Simulations suggested that it only worked as expected when the simulation showed matter that passed the inner boundary plunging into the black hole – confirmation of predictions made by the theory of general relativity. They also discovered that the reason light from infalling matter is observable is that it combines with light from the accretion disk.

“We've been ignoring this region because we didn't have the data,” said research scientist Andrew Mummery, lead author of the study published Thursday in the journal Monthly Notices of the Royal Astronomical Society. “But now that we have [the data], we couldn’t explain it any other way.”