How to Photograph a Black Hole
Black holes have long been depicted in film—with the first mention in the 1979 movie The Black Hole—but the first photo of a black hole was not taken until recently. That feat was accomplished in 2019, when astrophysicist at the Center for Astrophysics at Harvard, Sheperd Doeleman, and his team of researchers at the Event Horizon Telescope (EHT) captured these elusive phenomena.
Doeleman, founding director of the EHT, delivered The Sturm Memorial Lecture on April 22 in Ring Family Performing Arts Hall. The Sturm Memorial Lecture, endowed by the Kenneth Sturm ’40 in honor of Ruth Sturm, is an annual public lecture to bring the excitement of astrophysics and space science to the Wesleyan and local Middletown communities. He reviewed the history of supermassive black holes, how the EHT was developed, what we have learned so far about these mysterious entities, and what scientists hope to learn in the future.
“There are many things that human beings have done that are great; very few are profound,” said John Monroe Van Vleck Professor of Astronomy Edward Moran. “And many of you have attended certain lectures in the past, and I'm sure you found the speakers and their subjects to be interesting, fascinating, inspiring, amazing, incredible. What you're going to hear about tonight is profound.”
Famed physicist Albert Einstein first theorized that an observer should see a ring of light surrounding the black hole, formed by radiation emitted from hot gas in a black hole’s event horizon—a mathematical boundary point where matter can no longer escape from a black hole. The EHT’s research confirmed Einstein’s theory.
Black holes are nearly impossible to see because they are so dense light cannot escape their gravitational pull. There is also a strong interstellar medium, made up of iron plasma and ionized free electrons, that can scatter radio waves and make it difficult to visualize a black hole, Doeleman explained. Further research indicated a wavelength that made seeing a black hole possible, but with one problem—it would take a telescope that was 10,000 kilometers across.
“Of course, we can't build the telescope as large as the Earth, but you can simulate one,” Doeleman said. “What we did to capture the first image of a black hole was take radio telescopes at different points on the Earth and [point them at] the same black hole at the same time.”
The EHT team pointed the telescopes at a black hole in galaxy Messier 87, which is 54 million light years from Earth, and collected data. Once collected, the team lined up the data and fed them into a supercomputer to stitch an image together. The result was an image of a black center surrounded by a ring of light, with one side brighter than the other. The matter coming towards Earth appears brighter than the matter moving away from Earth, Doeleman explained, like how a train whistle is louder coming toward you than when it has passed by. Once the image was created, they were able to measure the mass of the black hole at 6.5 billion solar masses—or 6.5 billion times the size of our sun. The EHT team then duplicated its efforts with another black hole, this time at the center of the Milky Way Galaxy, in 2022.
“This allows us to study, most importantly, the details of the flow around the black hole for the first time,” Doeleman said. “We're making great inroads on understanding how black holes accrete, how they feed, how they launched these jets [of matter], and the composition of the plasma around the black hole.”
From here, the EHT team has its sights set on making a black hole movie—not the simulated kind seen in Interstellar—but a real moving visual of a black hole.
“We want to make black hole cinema a reality,” Doeleman said.
The lecture was sponsored by the Astronomy Department, Allbritton Center for the Study of Public Life, and the NASA Connecticut Space Grant Consortium. It was followed by a reception and telescope viewing at the Van Vleck Observatory.
