When scientists unveiled humanity’s first historic black hole image in 2019 – depicting a dark core encircled by a fiery aura of matter falling towards it – they thought even richer images and insights were waiting to come. be extracted 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 thrown from the back of the black hole by its intense gravity.
A team of researchers led by astrophysicist Avery Broderick used sophisticated imaging algorithms to essentially “remaster” the original imagery of the supermassive black hole at the center of the M87 galaxy.
“We turned off the spotlight to see the fireflies,” said Broderick, an associate faculty member at Perimeter Institute and the University of Waterloo. “We were able to do something profound – resolve a fundamental signature of gravity around a black hole.”
By essentially “peeling off” elements of the imagery, says co-author Hung-Yi Pu, an assistant professor at National Taiwan Normal University, “the environment around the black hole can then be clearly revealed.”
To do this, the team used a new imaging algorithm within the Event Horizon Telescope (EHT) THEMIS analysis framework to isolate and extract the distinct ring feature from the original observations of the M87 black hole – as well as to detect the telltale footprint of a powerful jet blasting outward from 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.
Black holes were long considered invisible until scientists brought them out of hiding with a global network of telescopes, the EHT. Using eight observatories on four continents, all pointed at the same spot in the sky and linked together by nanosecond synchronization, EHT researchers observed two black holes in 2017.
The EHT collaboration first unveiled the supermassive black hole in M87 in 2019, and then in 2022, the relatively small but tumultuous black hole at the heart of our own Milky Way galaxy, called Sagittarius A* (or Sgr A*). Supermassive black holes occupy the center of most galaxies, packing an incredible amount of mass and energy into a small space. Black hole M87, for example, is two quadrillion (i.e. two followed by 15 zeros) times more massive than Earth.
The M87 image scientists unveiled in 2019 was a landmark, but the researchers felt they could refine the image and glean new information 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 lurked beneath the surface. The resulting new image depicts the photon ring, made up of a series of progressively sharper sub-rings, which the team then stacked to get the full picture.
“The approach we took was to leverage our theoretical understanding of how these black holes look to build a custom model for the EHT data,” said Center for Astrophysics-based team member Dominic Pesce. | Harvard & Smithsonian. “This model decomposes the reconstructed image into the two elements that interest us most, so that we can study the two elements individually rather than mixed together.”
The result was possible because the EHT is a “computational instrument at its core,” said Broderick, John Archibald Wheeler Delaney Family Chair at Perimeter Institute. “It depends as much on algorithms as it does on steel. State-of-the-art algorithmic developments allowed us to probe key features of the image while rendering the rest in the native resolution of the EHT.
The researchers’ findings were published Aug. 16 in The Astrophysical Journal.
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