Washington, DC — Scientists unveiled the first-ever image captured of a black hole on April 10, a landmark achievement that was supported in part by a $7.2 million grant from the John Templeton Foundation. The image, which shows the light-ringed dark shadow of the black hole at the center of Messier 87 (M87), a massive galaxy in the Virgo star cluster, was captured using the Event Horizon Telescope (EHT), an array of seven observatories around the globe linked to create an earth-sized super-telescope.
Until this morning, all images of black holes were illustrations based on simulations and artistic interpretations of astrophysicists’ predictions. EHT director Sheperd Doeleman, who also heads Harvard’s Black Hole Initiative, revealed the image of M87’s black hole to a gathered crowd of scientists and members of the press. The image he presented was a near-perfect match for what the simulations had predicted. It showed a ring of light bulging at one side, the result of superheated gas swirling around the black hole’s event horizon — the point at which its gravity is so strong that nothing, including light, can escape. “We now know that a black hole that weighs 6.5 billion times what our sun does exists at the center of M87,” Doeleman said. “This is the strongest evidence we have to date for the existence of black holes.”
THE BLACK HOLE INITIATIVE
Scientific discoveries on the physical and symbolic scale of the black hole images are years in the making. Doeleman said that planning for the EHT began a decade ago, and the project eventually involved over 200 scientists from 60 institutes in more than 20 countries. Harvard’s Black Hole Initiative, which launched in 2016 with $7.2 million in funding from the John Templeton Foundation, served as a command center for the EHT project.
“We are delighted and honored that our philanthropic support has helped to enable the breakthrough seen today,” said Heather Templeton Dill, president of the John Templeton Foundation. “It’s an exciting new chapter in our work to foster discoveries in the natural sciences, and to spur reflection on the most profound questions facing humankind.”
Matthew Walhout, the foundation’s vice president for the natural sciences, agreed. “We’re proud to have supported this important work, which has confirmed the once radical-sounding predictions of Einstein’s theories,” he said. “This major discovery is just one result made possible through the foundation’s work to enable physicists and philosophers to collaborate to address fundamental questions on the nature of black holes.”
DATA’S LONG JOURNEY
The observations used to generate the images were taken in April of 2017, when the sophisticated equipment was finally in place and the weather cooperated at the telescope sites in Chile, Arizona, Spain, Hawaii, Mexico, and the South Pole. More than five petabytes of data were recorded on hard drives at the sites and flown to central processing facilities, where the data was be filtered to separate the signal from the noise. Since visible-wavelength light from the event horizon is absorbed by the gas clouds surrounding M87’s galactic center, the team focused on the one-millimeter wavelength — a few of those photons survived the 55 million-light-year journey from the black hole to Earth’s surface. EHT co-investigator Dan Marrone said that the data was simultaneously analyzed by four independent imaging teams, each of which used different algorithmic approaches to process the image. When the teams came together last summer, “What we saw in those images were four very similar pictures, looking almost exactly like the one you see today,” Marrone said. “It was a wonderful day for science.”
The final combined image is visually stunning, but in some ways its significance may be that it was more or less what the researchers had expected to see. Astrophysicist Avery Broderick, who introduced the EHT group’s preliminary interpretive findings, said that predictions based on Einstein’s theory of general relativity suggested that the event horizon shadow would be within 10 percent of a perfect circle. “When we began this expedition, we didn’t know what we would find,” Broderick said. “Today general relativity has passed another crucial test.”
Theoretical astrophysicist Sera Markoff, who offered reflections on the broader implications of the black hole image, noted that it tells us a lot about what different black holes have in common and how they might differ. “General relativity does not change with different black hole masses, but the impact will change a lot,” Markoff said. Using the shadow image, the EHT team determined that M87’s mass is equivalent to 6.5 billion suns. That result resolves a longstanding controversy about the black hole’s mass and now allows indirect measures of the mass to be calibrated with the observed data. “This will lead to better mass determinations for other more distant black holes where we can’t actually see the shadow,” Markoff said.
ENHANCING THE IMAGE
The EHT team is now working to process data from another stellar target, the dormant black hole Sagittarius A* (pronounced “A star”), which sits at the center of our own galaxy, the Milky Way. It is far closer than M87 — a mere 26,000 light years away — but is much harder to see because it is smaller and less active. The EHT’s imaging power is being increased as new telescopes are added to its network and data for even shorter wavelengths is gathered, paving the way for detailed observations about the extreme physical processes that occur around different types of black holes. “As with all great discoveries,” Doeleman said, “this is just the beginning.”
Learn more about the Event Horizon Telescope.
Explore other questions relating to the study of black holes at Harvard University’s Black Hole Initiative.
Watch Black Hole Hunters, a feature-length documentary about the observations behind the first black hole image. (Premiering Friday April 12 at 9pm ET/PT on the Smithsonian Channel).