Astronomers working on the Event Horizon Telescope (EHT) project have revealed the first picture of the black hole located at the center of our galaxy, the Milky Way. That memorable image is the result of five years of colossal work by more than 300 scientists around the world.
A supermassive black hole at the center of each galaxy
In 2017, EHT astronomers observed the center of the Milky Way, along with the distant galaxy M87. The latter is home to one of the biggest supermassive black holes known to this point. After two years of effort, the first picture of a black hole, that of galaxy M87, was revealed.
The work to process the data from the center of the Milky Way has been a lot more complex. The center of our galaxy is situated 27,000 light years from Earth, in the constellation Sagittarius. By analyzing the movement of stars in that region over a number of years, astronomers deduced that an invisible object, very dense and very massive, occupied the center of our galaxy. Named Sagittarius A* (Sgr A*), this object is an important source of radio wave emission.
What is a black hole?
Black holes are extremely dense celestial objects that nothing can escape from – even light – because of the enormous gravity they generate. They’re extremely difficult to observe, for the very reason that they emit no light.
It is therefore impossible to directly observe black holes, because they’re completely dark. However, these celestial monsters absorb the gas that comes too close, and form a bright ring. As it turns at great speed, the gas heats up and emits light. When the gas crosses an area called the event horizon, it is inexorably captured by the black hole creating a dark area at the center of the ring.
The black hole Sagittarius A*
Sagittarius A* is a small supermassive black hole, whose mass is four million times greater than the Sun’s, compared to that of M87, which totals 6.5 billion solar masses. The ring surrounding Sgr A* being much smaller, the orbiting matter inside takes just a few minutes to complete a loop. The pictures taken by EHT telescopes were very different from one another, a bit like when we photograph a puppy dog chasing its tail.
It has therefore been very difficult to analyze and combine the thousands of photos of Sgr A* taken by the telescopes and make a single clear picture. Scientists have had to use supercomputers and compile thousands of theoretical simulations of pictures of black holes to compare them with the observations.
That’s what was revealed on May 12, 2022. And already, the result obtained is fascinating astronomers.
Studying black holes
The first thing noticed is that, as is the case with M87, the picture of Sgr A* agrees admirably with Einstein’s theory of general relativity. Additionally, the images of the supermassive black holes of Sgr A* and of M87 have the same morphology.
These two examples will allow astronomers to study the way in which matter is absorbed by a black hole and how gravity behaves in such an extreme environment.
A new EHT telescopes observation campaign was carried out in March 2022. These additional data will make it possible to refine the images obtained and study the role of supermassive black holes in the formation and evolution of galaxies.