First black hole image puts Einstein's famous theory to the test

Another extreme test of general relativity, another win for Einstein.

Jackson Ryan Former Science Editor
Jackson Ryan was CNET's science editor, and a multiple award-winning one at that. Earlier, he'd been a scientist, but he realized he wasn't very happy sitting at a lab bench all day. Science writing, he realized, was the best job in the world -- it let him tell stories about space, the planet, climate change and the people working at the frontiers of human knowledge. He also owns a lot of ugly Christmas sweaters.
Jackson Ryan
3 min read

Stare into the abyss, the abyss stares back. 

Lia Medeiros

You'd be crazy to bet against Albert Einstein and his theory of general relativity. Formulated over 100 years ago, it reasons that gravity is the warping of space and time. Since Einstein conceived the theory, test after test -- of eclipses and gravitational waves, for instance -- has supported it. But if you need any more convincing that Einstein was on the money, researchers with the Event Horizon Telescope collaboration have just revealed more evidence that his theory stands up, even under some of the most extreme conditions in the universe. 

In a study, published in the journal Physical Review Letters on Thursday, researchers from the EHT collaboration analyzed the images of the supermassive black hole that lies at the heart of the Messier 87 galaxy to put Einstein's theory to the test again. That black hole, M87*, is the same black hole researchers used to create the first-ever image of a black hole by the EHT team in 2019. 

"This is really just the beginning," said Lia Medeiros, an astrophysicist at the Institute for Advanced Study and co-author on the study, in a press release. "We have now shown that it is possible to use an image of a black hole to test the theory of gravity,"

With the images acquired of M87*, which is about 6.5 billion times more massive than the sun, the research team were able take a closer look at how the massive black hole bends spacetime. A black hole does not emit any light, but it is surrounded by a hot disc of accreting gas around the event horizon -- the point of no return. This hot, bright gas gives the black hole its shadow. When researchers took the first image of M87*, it was visible against a bright orange backdrop and agreed with the predictions made in the theory of general relativity.

The team essentially tried to disprove the theory of general relativity in the new research. While it has been shown to align with observations of the cosmos time and again, it still hasn't been reconciled with a grander theory of how gravity works. So scientists keep looking for ways to show it might break down. But it doesn't break down when they look at the size of the black hole shadow, it holds up.

It seems like Einstein can't lose. The new result shows that even under the most extreme conditions -- right next to a black hole -- general relativity holds up. And the EHT collaboration isn't done yet.

See also: These telescopes work with your phone to show exactly what's in the sky  

The Event Horizon Telescope is actually a series of telescopes across the world that have been fixated on two supermassive black holes: M87* and the black hole at the center of the Milky Way, Sagittarius A*. When images of Sgr A* are released, it will provide researchers with yet another opportunity to put Einstein's theory to the test. 

"This test will be even more powerful once we image the black hole in the center of our own galaxy and in future EHT observations with additional telescopes that are being added to the array," said Medeiros.

What will those observations show? Probably a good idea to bet on Einstein and his theory of general relativity once again.

Watch this: How black holes swallow light, warp space-time and blow your mind