A very important step has just been taken in the field of astronomy. For the very first time, we have managed to obtain an image of Sagittarius A*, the giant black hole at the center of our galaxy. This feat was achieved by the EHT telescope or Event Horizon Telescope.
This historic image is confirmation that there is indeed a black hole at the center of the Milky Way. According to Feryal Özel, an astrophysicist at the University of Arizona, until now, there has never been an image proving that the giant cosmic object which is at the center of our galaxy is a black hole. For his part, Ryan Hickox, an astrophysicist at Dartmouth College, and who is not a member of the EHT team, declared that it was a “staggering performance”.
The image of Sagittarius A* was recorded in the sub-millimetre radio wave range, and according to the scientists, the task was not at all easy.
A very complicated job
The EHT had already made headlines in 2019 after successfully producing the first-ever image of a black hole’s event horizon. This was the black hole that sits at the center of the elliptical galaxy Messier 87. While collecting data to form the black hole image of M87, the EHT was also making observations of Sagittarius A*. But it turned out that producing an image of the latter was much more complicated than for the black hole of M87.
According to the researchers, water in the Earth’s atmosphere can absorb the sub-millimeter radio waves used by the telescope. Additionally, gas and dust within 27,000 light-years from Earth to the black hole can scatter sub-millimeter waves and blur the image.
There was also an additional difficulty compared to observing the M87 black hole. Indeed, the latter is “voracious” and therefore appears brighter since it absorbs a large quantity of gas. Sagittarius A*, for its part, presents a lower flow of matter, and it thus appears less visible.
According to Özel, it was not easy to arrive at this image. It took them years to refine it and confirm that they got it.
A set of telescopes
To get this image of Sagittarius A* and the previous black hole, the scientists used a technique known as Very Long Baseline Interferometry. This technique allows astronomers to combine data from radio telescopes around the world as if all these telescopes were forming a single giant telescope, the largest on Earth.
At the time of the observations, the telescope array consisted of 8 elements. This configuration means that the maximum “aperture” of the EHT to observe Sagittarius A* was 10,700 km.
Other observations will be made in the future to try to make the images sharper. This will serve to better understand the physics of turbulence at the level of the ring that surrounds the black hole, but also the effects that the black hole has on the galaxy that surrounds it.