UT scientists have shown that black holes are really black — everything goes in and nothing comes out.

Einstein’s theory of general relativity suggests that there is a boundary known as the event horizon around the black hole beyond which nothing can escape the black hole’s enormous gravity.

“There’s no astrophysical test for most black holes. We know that matter falls into the holes, but it’s actually not easy to test whether there’s anything that comes out,” said Wenbin Lu, lead author and graduate student in astronomy.

Lu and his team theorized that if a black hole actually has a surface instead of an event horizon, when a star falls into it, a lot of radiation, heat and light would be emitted by the collision.

They observed supermassive black holes at the center of local galaxies over the period of three and a half years using the Pan-STARRS telescope in Hawaii. They expected to see evidence of more than 10 collisions if black holes have a hard surface.

“We found none,” Lu said. “Stars, when they fall into black holes, they fall silently. They simply get swallowed, and nothing escapes.”

Lu said this isn’t absolute proof that black holes are inescapable, but that their work supports Einstein’s theories.

Astrophysics professor Pawan Kumar said that this aspect of black holes hasn’t been tested until recently, since stars falling into supermassive black holes have only been observed since 2007.

“The theoretical idea we proposed in our recent paper certainly could have been proposed several decades ago,” Kumar said. “However, no one to my knowledge carried out the analysis we did in our recent paper.”

Lu said they first got the idea after studying the interactions between stars and lower-mass black holes, and that he was curious about what happens when larger mass black holes swallow stars.

The next step for the team is to use more powerful telescopes and study more black holes to improve their findings that black holes do indeed have an event horizon, Kumar said.