It took a decade to produce the first photograph of a black hole, the one at the center of the Messier 87 galaxy (the black hole is also known as M87*) some 55 million light-years away. Its event horizon is nearly 25 billion miles wide, with a mass roughly that of 6.5 billion Suns.
Though Sagittarius A* — or Sgr A* for short — is a mere 27,000 light years away from Earth, it has less than 0.1% of M87*'s mass. If it wasn't conveniently located in our own galaxy, it would have been nearly impossible to photograph. Bouman likened it to standing in Los Angeles and taking a photo of a grain of salt in New York.
"It's a gentler, more cooperative black hole than we had hoped for," said Feryal Özel, a University of Arizona astronomer and founding member of the telescope consortium. "We love our black hole."
Indeed, the pictures provide the strongest evidence to date for Einstein's theory of general relativity. With Sgr A* in particular, the size and shape of the ring surrounding the event horizon is remarkably consistent with what scientists predicted based on Einstein's theory.
"They're so different in so many ways, yet the same theory of gravity actually explains" the shape of both images, Bouman said. "And that is a big result. It's actually very exciting that they look very similar."
A popular classroom model of a black hole offers a useful way to visualize this cosmic phenomenon. Picture the fabric of space-time as a sheet of plastic wrap pulled tight, and Earth as a tennis ball dropped into its center. The ball will create a slight curve in the film, just as our relatively modest-sized planet does to space-time.
A ball of steel, however, will bend the film much further. If the ball is heavy enough, the film will sag so much that any other objects will roll inescapably down toward the heaviest one. That's what black holes do to time and space.
"Black holes are not the big cosmic vacuum cleaners Hollywood likes to portray them as," Bouman said.
The smaller and less efficient Sgr A* is more likely a better representative of the typical black hole in the universe than the ultra-massive M87*, Bouman said.
UCLA astronomer Andrea Ghez was awarded the Nobel Prize in 2020 for discovering Sgr A*. The image the EHT produced was "remarkably similar" to the supermassive black hole she and her colleagues theorized was at the center of this galaxy.