Harvard history of science professor Peter L. Galison, a collaborator on Event Horizon Telescope (EHT), said that scientists proposed theoretical arguments for black holes as early as 1916. It was not until the 1970s, however, that researchers substantiated the theory by observing extremely dense areas of matter. Scientists announced in 2016 that, for the first time, they had detected gravitational waves — which many argued were produced by black holes merging, and therefore were evidence that black holes exist.
Scientists had long struggled to capture a photograph of a black hole — a region of space with a gravitational pull so strong that not even light can escape it. The image revealed Wednesday is comprised of a glowing orange ring on a black background.
The image marked the culmination of years of work undertaken by a team of 200 scientists in 59 institutes across 18 countries. The project, to which other scientists at Harvard’s Black Hole Institute also contributed, drew on data collected by eight telescopes whose locations range from Hawaii to the South Pole. In order to construct this image digitally, the team of astronomers at EHT created the equivalent of a lens the size of planet Earth by integrating data from all the telescopes that were part of the project that’s 4,000 times more powerful than the Hubble Space Telescope.
This particular elliptical galaxy, M87, has a jet that emanates from the vicinity of the black hole, said Abraham “Avi” Loeb, the founding director of the Black Hole Initiative and the chair of Harvard’s Astronomy Department, of the galaxy in which the black hole was found. “What you’re seeing is the shadow of the black hole on the background of the emission from the hot gas at the base of the jet.”
Astronomers have theorized that the M87 black hole grew to its massive size by merging with several other black holes. M87 is the largest, most massive galaxy in the nearby universe, and is thought to have been formed by the merging of 100 or so smaller galaxies. The M87 black hole’s large size and relative proximity, led astronomers to think that it could be the first black hole that they could actually “see.”
“Getting this system of at least eight to ten different telescopes, all entirely different, all working together with receivers and data recording systems, and particularly the clocks — the atomic clocks—to be all, if you want to think of it, in synchrony was an amazing technical achievement,” Harvard astronomy professor Jonathon E. Grindlay said.
He said he does not think it would have been possible to generate this image even a decade ago given the sophisticated technology needed to handle the five petabytes of data – the equivalent of 5 million gigabytes — involved in creating the picture.
Galison said he thinks the image unveiled will be more compelling evidence of the existence of black holes to the public than some of the more technical data. “It’s amazing to be able to say, here’s the black hole, the size of our solar system, and bigger, and it has the mass of six and a half billion suns,” he said.
“[The black hole] was an object that was predicted to exist 100 years ago,” he said. “And the fact that it’s taken us hundred years to get a clear picture of them is not a measure of how lazy and slow scientists are. It’s a measure of how huge the problem is, and with what precision and depth we’re understanding the universe around us. It’s something I’ve been thinking about my entire scientific life, and now I’ve seen it,” he added.
Though Loeb said the image is certainly historic, he said the picture largely corroborated his team’s prior predictions of what a black hole would look like if digitally rendered. “So the surprising result is that there is nothing surprising,” Loeb said.
This first-ever image prompted such excitement in the public because black holes are a cultural phenomenon imbued with metaphor and mythology, according to Galison. “There’s something paradoxical, intriguing, frightening, and imagination-provoking about black holes,” he said.
The Harvard scientists say they think new discoveries are still on the horizon. “There are some real questions about destruction, what’s inside a black hole, and so on, that we might get to the very edge of — or even probe — with this Event Horizon Telescope,” Strominger said.