Supermassive black hole at heart of Milky Way pictured for the first time

Mayank Chhaya-

Mayank Chayya

A team of astronomers has zeroed in on a long-theorized supermassive black hole at the heart of the Milky Way and produced its first picture. “The gentle giant”, as it has been described, has over long periods devoured the equivalent of 4 million suns whose only remnant is their gravity and a brutalized space-time.

The announcement by the U.S. National Science Foundation (NSF) along with the Event Horizon Telescope Collaboration in Washington, D.C. today, answers a greatly debated theory that the object known as Sagittarius A* (Sgr A*, pronounced “sadge-ay-star”) is indeed a black hole.

“This result provides overwhelming evidence that the object is indeed a black hole and yields valuable clues about the workings of such giants, which are thought to reside at the center of most galaxies. The image was produced by a global research team called the Event Horizon Telescope, or EHT, Collaboration, using observations from a worldwide network of radio telescopes,” the NSF said.

“Although we cannot see the black hole itself, because it is completely dark, glowing gas around it reveals a telltale signature: a dark central region (called a “shadow”) surrounded by a bright ring-like structure. The new view captures light bent by the powerful gravity of the black hole, which is four million times more massive than our Sun,” it said.

Yet again the black hole proved predictions based on Albert Einstein’s Theory of General Relativity. “We were stunned by how well the size of the ring agreed with predictions from Theory of General Relativity,” said EHT Project Scientist Geoffrey Bower from the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei.

“These unprecedented observations have greatly improved our understanding of what happens at the very center of our galaxy and offer new insights on how these giant black holes interact with their surroundings,” he said.

Located 27, 000 light-years away from Earth, the data from the black hole took those many years traveling at the speed of light of about six trillion miles a year. The distance works out to be an incomprehensible 162,000 trillion miles.

Since it is so far, the black hole “appears to us to have about the same size in the sky as a donut on the Moon.”

The NSF said to image it, the team created the powerful EHT, which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope

The breakthrough follows the EHT collaboration’s 2019 release of the first image of a black hole, called M87*, at the center of the more distant Messier 87 galaxy.

The two black holes look remarkably similar, even though our galaxy’s black hole is more than a thousand times smaller and less massive than M87*. “We have two completely different types of galaxies and two very different black hole masses, but close to the edge of these black holes they look amazingly similar,” Sera Markoff, Co-Chair of the EHT Science Council and a professor of theoretical astrophysics at the University of Amsterdam, the Netherlands, said. “This tells us that General Relativity governs these objects up close, and any differences we see further away must be due to differences in the material that surrounds the black holes.”

Explaining the specifics the NSF said, “This achievement was considerably more difficult than for M87*, even though Sgr A* is much closer to us.” It quoted EHT scientist Chi-kwan (‘CK’) Chan, from Steward Observatory and Department of Astronomy and the Data Science Institute of the University of Arizona, U.S., as saying: “The gas in the vicinity of the black holes moves at the same speed — nearly as fast as light — around both Sgr A* and M87*. But where gas takes days to weeks to orbit the larger M87*, in the much smaller Sgr A* it completes an orbit in mere minutes. This means the brightness and pattern of the gas around Sgr A* was changing rapidly as the EHT Collaboration was observing it — a bit like trying to take a clear picture of a puppy quickly chasing its tail.”

The researchers had to develop sophisticated new tools that accounted for the gas movement around Sgr A*. While M87* was an easier, steadier target, with nearly all images looking the same, that was not the case for Sgr A*. The image of the Sgr A* black hole is an average of the different images the team extracted, finally revealing the giant lurking at the center of our galaxy for the first time.

“The effort was made possible through the ingenuity of more than 300 researchers from 80 institutes around the world that together make up the EHT Collaboration. In addition to developing complex tools to overcome the challenges of imaging Sgr A*, the team worked rigorously for five years, using supercomputers to combine and analyze their data, all while compiling an unprecedented library of simulated black holes to compare with the observations,” the Foundation said.

“This image is a testament to what we can accomplish when as a global research community, we bring our brightest minds together to make the seemingly impossible, possible. Language, continents and even the galaxy can’t stand in the way of what humanity can accomplish when we come together for the greater good of all. This is a historic moment where we see the black hole at the heart of our Milky Way as a capstone achievement following decades of intense curiosity-driven discovery research. NSF is proud to be an international partner that invests in this innovative research and the infrastructure that makes such fantastic discoveries possible,” said NSF Director Sethuraman Panchanathan.