Sophisticated algorithms have discerned a sharp ring of light created by photons striking the back of a supermassive black hole in vivid confirmation of the theoretical prediction.
When scientists released humanity’s first historic image of this black hole in 2019, depicting a dark core at the center of the galaxy M-87 surrounded by a fiery aura of material falling toward it, they believed there were images and even richer insights waiting to be pulled from the data.
The simulations predicted that, hidden behind the glow of the diffuse orange glow, there should be a thin, bright ring of light created by photons flung around the back of the black hole by its intense gravity.
A team of researchers led by astrophysicist Avery Broderick of the University of Waterloo has now been able to “resolve a fundamental signature of gravity around a black hole,” he said. “We turned off the searchlight to see the fireflies,” he added in a statement.
Essentially, by “peeling off” elements of the images, says co-author Hung-Yi Pu, an assistant professor at National Taiwan Normal University, “the environment around the black hole can be clearly revealed.”
To achieve this, the team employed a new imaging algorithm within the Event Horizon Telescope’s (EHT) THEMIS analysis framework to isolate and extract the distinctive ring feature from the original observations of black hole M87, as well as to detect the telltale fingerprint. of a powerful jet shooting out of the black hole.
The researchers’ findings confirm theoretical predictions and offer new ways to explore these mysterious objects, which are thought to reside at the heart of most galaxies.
For a long time, black holes were considered invisible until scientists brought them out of hiding with a world-spanning network of telescopes, the EHT. Using eight observatories on four continents, all pointing to the same point in the sky and connected to each other with nanosecond synchronization; EHT researchers observed two black holes in 2017.
The EHT collaboration first revealed the supermassive black hole in M87 in 2019 and then, in 2022, the comparatively small but tumultuous black hole at the heart of our own Milky Way galaxy, named Sagittarius A star. Supermassive black holes occupy the center of most galaxies, packing an incredible amount of mass and energy into a small space. The black hole M87, for example, is two thousand trillion times more massive than Earth.
The M87 image scientists unveiled in 2019 was a milestone, but researchers felt they could improve the image and gain new insights by working smarter, not harder. They applied new software techniques to reconstruct the original 2017 data in search of phenomena that theories and models predicted were lurking just below the surface.
The resulting new image shows the ring of photons, made up of a series of increasingly sharper sub-rings, which the team then stacked to get the full image.
“The approach we took involved leveraging our theoretical understanding of what these black holes look like to build a custom model for the EHT data,” said Dominic Pesce, a member of the team based at the Center for Astrophysics | Harvard and Smithsonian. “This model breaks down the reconstructed image into the two pieces we are most interested in, so we can study both pieces individually instead of combining them.”
The result was possible because the EHT is a “computational instrument at its core,” Broderick said. “It’s as reliant on algorithms as it is on steel. State-of-the-art algorithmic developments have allowed us to test key image features while rendering the rest in native EHT resolution.” The researchers’ findings were published in The Astrophysical Journal.