An image of the supermassive black hole at the heart of the Milky Way has been captured, giving the first direct glimpse of the “gentle giant” at the center of our galaxy.
The black hole itself, known as Sagittarius A*, cannot be seen because no light or matter can escape its gravitational grasp. But its shadow is traced by a luminous, hazy ring of light and matter that swirls over the precipice at near light speed.
The image was captured by the Event Horizon Telescope (EHT), a network of eight radio telescopes covering sites from Antarctica to Spain and Chile, which produced the first image of a black hole in a galaxy. called Messier 87 in 2019.
Professor Sera Markoff, an astrophysicist at the University of Amsterdam and co-chair of the EHT Scientific Council, said: “The Milky Way black hole was our main target, it is our closest supermassive black hole and that’s why we decided to do it. thing first. It’s been a 100 year search for these things and so scientifically it’s a huge deal.
The image provides compelling evidence that there is a black hole at the center of the Milky Way, which was the working hypothesis of mainstream astronomy. A minority of scientists had continued to speculate on the possibility of other exotic objects, such as bosonic stars or clusters of dark matter.
“I’m personally happy that this really shows that there is definitely a black hole at the center of our galaxy,” said Dr Ziri Younsi, a member of the EHT collaboration based at University College London.
To the untrained eye, the latest image might look roughly similar to that of the black hole, M87*, but the two objects are starkly different, according to the EHT team.
Sagittarius A* consumes only a trickle of matter, contrary to the typical portrayal of black holes as violent, voracious monsters of the cosmos. “If SgrA* were a person, it would only consume one grain of rice every million years,” said Michael Johnson of the Harvard-Smithsonian Center for Astrophysics.
M87*, on the other hand, is one of the largest black holes in the universe and features vast, powerful jets that shoot light and matter from its poles into intergalactic space.
“Sgr A* gives us a look at the much more standard state of black holes: silent and at rest,” Johnson said. “[It] it’s exciting because it’s common.
The latest observations also seem to show that the angle of rotation of our black hole is not perfectly aligned with the galactic plane, but is off by about 30 degrees, and suggests spectacular magnetic activity similar to that observed. in the atmosphere of the sun. Beyond the science, astronomers have recognized an emotional connection to finally seeing the enigmatic object around which our home galaxy revolves.
“It’s another donut, but it’s our donut,” Younsi said.
Although local in astronomical terms to 26,000 light-years away, observing SgrA* has proven more difficult than expected. The team spent five years analyzing data acquired during a fortuitously clear sky across multiple continents in April 2017.
Sagittarius A* is relatively small, meaning dust and gas from its accretion disk orbit in minutes rather than weeks, creating a moving target from sighting to sight. Markoff compared the sightings with attempting to photograph a puppy chasing its tail using a camera with a slow shutter speed. Scientists also had to look through the galactic plane and filter out intervening stars and dust clouds from their images. A combination of these factors – and perhaps an extreme black hole phenomenon – explains the bright spots in the image.
“We didn’t anticipate how elusive and elusive it would be,” Younsi said. “It was definitely a difficult photo to take. It’s hard to overstate that.
The EHT picks up radiation emitted by particles inside the accretion disk that are heated to billions of degrees as they orbit the black hole before plunging into the central vortex. The mottled halo in the image shows light bent by the powerful gravity of the black hole, which is 4m times more massive than that of our sun.
Ultimately, scientists hope that observing a range of black holes – fairly dormant giants like ours and turbulent giants like M87* – might help answer a chicken-and-egg question about the evolution of galaxies.
“It’s an open question in galactic formation and evolution. We don’t know which came first, the galaxy or the black hole,” said Professor Carole Mundell, an astrophysicist at the University of Bath who is not part of the EHT collaboration.
“From a technology perspective, it’s mind-boggling that we can do this,” she said of the latest footage.
The EHT team’s findings are published Thursday in a special issue of Astrophysical Journal Letters.