New image answers many questions about our galaxy’s black hole and reveals some mysteries

after more more than five years of data modeling, analysis, and even transporting hard drives around the world, astronomers have finally freed the first-ever snapshot of the black hole at the center of our galaxy.

Astronomers have long suspected that an invisible restaurant some 27,000 light-years from Earth is gobbling up starlight, but the new image is the first tangible confirmation of that hunch. Appointed Sagittarius A*or Sgr A* for short, this supermassive black hole appears donut-shaped in its portrait with several bright spots along its back.

Lindy Blackburn is a radio astronomer at the Center for Astrophysics | Harvard & Smithsonian and one of the scientists responsible for analyzing the data collected by the Event Horizon Telescope (EHT) collaboration, which captured and assembled the latest image. Beyond the wonder of the image itself, Blackburn says this discovery will also play an important role in advancing the scientific understanding of black holes.

“Now that we know it’s possible to image the black hole at the center of our galaxy, we’re working towards a next-generation EHT,” Blackburn said.

Prior to the EHT image, the central image from NASA’s Chandra X-ray Telescope was one of the best glimpses of the mysterious black hole at the center of our galaxy. X-rays: NASA/CXC/SAO; IR: NASA/HST/STScI. Inset: Radio (EHT Collaboration))

What scientists have understood — Black holes in science fiction are often portrayed as swirling voids or black chasms poised to sweep spacecraft across their event horizon to a point of no return, much like the explorers of ancient myths falling from the edge of a flat Earth.

However, recent groundbreaking work by the EHT has revealed that this representation may be a bit of an exaggeration. Thanks to the first image of the M87 black hole released by the collaboration in 2019, astronomers thought black holes appeared to be more doughnut-shaped in reality, with blackness in the center and outside. Because black holes themselves are still invisible to us and our telescopes, the donut shape highlights the heat given off by matter as it zips around the black hole.

Seeing that Sgr A* had the same donut shape as M87 confirmed to astronomers that supermassive black holes of vastly different sizes — M87 is more than 1,000 times more massive — had the same general structure. Blackburn says the appearance of Sgr A* also confirmed some long-held scientific theories.

“One of the most striking features of the Sgr A* image is that the size of its lensed emission ring perfectly matches that predicted by general relativity,” he says.

Blackburn also says that the bright spots on Sgr A* weren’t much of a surprise either and might reflect the dynamic plasma surrounding the black hole.

“We would expect these characteristics to vary over the course of a night,” he says. “Future observations should reveal whether this is indeed the case.”

A few surprises — However, not all of Sgr A*’s findings were exactly as scientists predicted. The first surprise was the ring’s “relatively even distribution of brightness”, suggesting that it could be oriented head-on with its axis of rotation pointed towards Earth. The black hole is also “curiously” out of alignment with the galaxy’s midplane, Blackburn says.

Another unexpected finding uncovered through Sgr A* imaging was that the level of variability in some of its measurements was lower than predicted by computer simulations.

This means “there is something we don’t quite understand about the behavior of plasma in the accretion flow,” says Blackburn.

The accretion disks around black holes are the messy crumbs left over from swallowing their meals. A better understanding of these discs could help scientists study the behavior of black holes as a whole, a subject still riddled with mysteries.

And after – With two black holes successfully resolved, Blackburn says the EHT has big plans to study these objects next.

“We are working towards a next-generation EHT that will actually be able to capture movies from a source at multiple frequencies, revealing the inflow and outflow dynamics near the boundary of a black hole as well as the nature of flares” , he said.

One thing is certain: the science of black holes will only become more exciting in the years to come.

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