First photo of a supermassive black hole in the center of the Milky Way • The Register

Astronomers have captured a clear image of the gigantic supermassive black hole at the center of our galaxy for the first time.

Sagittarius A*, or Sgr A* for short, is 27,000 light years from Earth. Scientists have known for a while that there is a mysterious object in the constellation Sagittarius emitting strong radio waves, although it wasn’t really discovered until the 1970s. Although astronomers have managed to characterize some properties of the object, the experts did not know exactly what they were looking at.

Years later, in 2020, the Nobel Prize in Physics was awarded to a pair of scientists, who mathematically proved that the object must be a supermassive black hole. Now their work has been experimentally verified in the form of the very first shot of Sgr A*, captured by more than 300 researchers working at 80 institutions as part of the Event Horizon Telescope collaboration.

Doesn’t seem so gigantic to us… The photo of Sagittarius A*. Click for much larger. Source: EHT Collaboration

This gathering of somewhat fuzzy orange blobs may not look impressive at first glance, but the shape and structure are the hallmarks of a supermassive black hole: a circular donut-like shape; the inner hole marks the edge or event horizon and is surrounded by a bright ring of radiation.

Eight ground-based telescopes located around the world were used to capture light from Sgr A* as of 2017. Researchers gathered 3.5 petabytes of observations and fed them into complex image processing algorithms running on supercomputers to build the image. The data from these telescopes must be carefully compared and processed; scientists must take into account factors such as the position of the instruments and the rotation of the Earth to build a stable and direct image.

“The mass and the distance of the object were known very precisely before our observations”, mentioned Luciano Rezzolla, professor of theoretical astrophysics at Goethe University Frankfurt, this week.

“We therefore used these strict constraints on the size of the shadow to exclude other compact objects – such as bosonic stars or wormholes – and concluded that: ‘What we see definitely looks like a black hole’ .

Rezzolla said constructing the image from telescopes is like trying to form a photo of a mountain peak from a series of time-lapse images; as the clouds pass and the sun rises and sets, the peak changes from plane to plane. The mountain top in this case is a supermassive black hole that is not only far, far away and tiny but also invisible.

Richard Anantua, assistant professor of physics and astronomy at the University of Texas at San Antonio, described the algorithms applied to the telescope observations. “In order to convert sparse data into images, we use established methods like the CLEAN algorithm to remove the beam point spread function intrinsic to the observing instrument,” he said. The register. “We also confirm our images by maximum likelihood methods, including priors for smoothness, sparseness, and maximum entropy.”

This code was executed on various clusters of supercomputers. “We used a wide variety of research computing facilities – both connected to EHT-affiliated universities and other institutions. Some of the facilities primarily used include the Black Hole Cluster at the University of Illinois at Urbana-Champaigne and the Texas Advanced Computing Cluster and the Open Science Grid,” he added.

Sgr A* bears a strong resemblance to M87*, a 6.5 billion solar mass supermassive black hole located in the M87 galaxy 50 million light-years away. Scientists believe that the two images taken by the EHT collaboration indicate that all types of black holes look alike, regardless of size, as they are governed by the laws of Einstein’s theory of general relativity.

“We now have a coherent picture that makes it look like general relativity works at both ends of supermassive black holes,” mentioned Kazunori Akiyama, a researcher at MIT’s Haystack Observatory.

Armed with these images, astronomers can now compare the two objects to learn more about supermassive black holes and their effects. “We are now dealing with images of a black hole population, so we are able to study black hole demography. Both images have global ring structures, but only M87* has an unbalanced azimuth profile. Sgr A* has flux coherency spots evenly distributed over the entire ring,” Anantua told us.

The boffins of the ETH collaboration have their sights set on several supermassive black holes they think they can image, such as the possible binary object OJ 287, 3.5 billion light-years away, Anantua said.

Research from the ETH collaboration detailing everything from the shadow, mass and shape of Sgr A* to how the image was captured and processed has been published in numerous academic publications listed here. ®

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