This is the first image of the black hole at the heart of our galaxy
Astronomers have unveiled the first image of the supermassive black hole at the center of our own galaxy, The Milky Way. This result provides overwhelming evidence that the object is indeed a black hole and yields valuable clues about the workings of such giants, thought to reside at the center of most galaxies.
Supermassive black holes are thought to reside at the center of most galaxies in the universe, including our own galaxy, the Milky Way.
Now, a global research team has produced a first ever image of a Milky Way black hole. The research team is called the Event Horizon Telescope (EHT) Collaboration, and the researchers have used observations from a worldwide network of radio telescopes.
About European Horizon Telescope
An international collaboration dedicated to make images of black holes and their immediate surroundings and to understand their physics. The telescope is named after the “event horizon”; the boundary of the black hole beyond which no light can escape.
- This is a groundbreaking achievement, and it was a long time in the making. We really needed to innovate to make this possible, said University of Southern Denmark physicist Roman Gold, who led the efforts one of four imaging teams (team THEMIS).
First, visual evidence
Scientists had previously seen stars orbiting around something invisible, compact, and very massive at the center of the Milky Way. This strongly suggested that this object, known as Sagittarius A* (or Sgr A*), is a black hole, and the new image provides the first direct visual evidence of it.
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 image captures light bent by the powerful gravity of the black hole, which is four million times more massive than our Sun.
- It is a huge breakthrough and a tremendous achievement to finally resolve the dot of mass that led to the 2020 Noble Prize for the discovery of a supermassive compact object at the center of our galaxy. With this new zoomed-in view we can see that it really looks like a black hole as Einstein's theory predicts it!, said Roman Gold.
With this new zoomed-in view we can see that it really looks like a black hole as Einstein's theory predicts it!
The EHT team's results are published in a special issue of The Astrophysical Journal Letters.
Because the black hole is about 27,000 light-years away from Earth, it appears to us to have about the same size in the sky as a donut on the Moon. 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 EHT observed Sgr A* on multiple nights, collecting data for many hours in a row, similar to using a long exposure time on a camera. The breakthrough follows the EHT collaboration’s 2019 release of the first image of a black hole, called M87*, at the centre 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*.
Fast moving gas
This achievement was considerably more difficult than for M87*, even though Sgr A* is much closer to us.
EHT scientist Chi-kwan Chan, from Steward Observatory and Department of Astronomy and the Data Science Institute of the University of Arizona, USA, explains:
- 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, he says and elaborates:
- 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.
Had to develop new tools
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.
It was a bit like trying to take a clear picture of a puppy quickly chasing its tail
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.
Progress on the EHT continues: a major observation campaign in March 2022 included more telescopes than ever before. The ongoing expansion of the EHT network and significant technological upgrades will allow scientists to share even more impressive images as well as movies of black holes in the near future.
Meet the researcher
Roman Gold is an Assistant Professor at the Department of Physics, Chemistry and Pharmacy. His research is centered around nature's most compact objects; black holes and neutron stars.