The Event Horizon Telescope has managed to give us a peek into the supermassive black hole at the heart of the Milky Way. Here is what we have unveiled so far about Sagittarius A*.
Black holes are some of the most strangest and incredibly elusive cosmic elements that have long evaded mankind. In fact, the first references to black holes were in the theoretical predictions made by the famous genius, Albert Einstein, in his general theory of relativity back in 1916. It was only in 1964 that the first black hole, Cygnus X-1, was discovered in the skies, situated within the Milky Way in the constellation of Cygnus. Astronomers detected Cygnus X-1 with a sounding rocket that was able to identify X-rays emanating from the black hole’s region. It was not until 1971, when the astronomers deduced that the X-rays were originating from a black hole devouring a bright star.
But 12 May 2022 saw a historic moment when for the first time we were able to capture the image of the supermassive black hole that sits at the heart of our Milky Way, Sagittarius A*. The Event Horizon Telescope was able to gather and merge their data to form the blurry photograph we have of Sagittarius A*. Despite the lack of clarity, it took the best instruments using their utmost ability to get the photo.
The image was not an easy one to take, considering that we are trying to capture a snapshot of a cosmic event, occurring 27,000 light-years away, that is also a moving target. Apart from the distance itself, Sagittarius A*’s rate of sucking in material was much more weak that translated into a fainter glow of light from the black hole.
Sagittarius A* has been the main target for black hole hunters for many years. And for the longest time, it has only existed in theory. The image we have now is the first photograph we have of our Milky Way’s largest black hole, thus confirming its existence. But this is not the first image we have of a black hole itself.
The Event Horizon telescope (EHT), which is a network of planet-wide group of eight radio telescopes located in several areas from Antarctica to Spain, computed humankind’s first image of a black hole in the galaxy, Messier 87 (M87), back in 2019. What the EHT captured of the M87 was an incredible image of a bright all-consuming black hole in the centre of M87, about 55 million light-years from Earth. The EHT was able to pick up the strong glow of light emanating from the edge of the black hole’s event horizon.
This light comes from the black hole feeding on materials from its environment, such as stars and asteroids. When the material moves too close to the event horizon, nothing can escape from being sucked into the black hole and being shredded apart by the immense gravity. Not even light.
However, in comparison to the M87, Sagittarius A* seems to be “eating” much less. According to Harvard astrophysicist Michael Johnson, the black hole was only consuming a trickle of material. Johnson adds, “Sagittarius A* is giving us a view into the much more standard state of black holes: quiet and quiescent. [It] is exciting because it’s common.” But more importantly, this image dispels the idea that all black holes are aggressive, voracious monsters. Maybe, they can be quiet, too.