Pontificia Universidad Católica de Chile (UC): Astronomers achieve first image of black hole in the center of the Milky Way

It has a mass equivalent to that of four million suns and is located 27,000 light years away from Earth. Until now, astronomers only knew of the existence of Sagittarius A* -the supermassive black hole located in the center of our galaxy- , due to the behavior of the stars and objects around it, which showed signs of orbiting around something invisible. , compact and very massive.

Now, the science team of the Event Horizon Telescope (EHT) initiative has announced that they have obtained the first direct visual evidence of the supermassive black hole at the center of our Milky Way . It is an international effort in which more than 300 researchers from 80 institutes around the world participated, including the Center for Astrophysics and Related Technologies (CATA) , and the Department of Astronomy of the University of Concepción and the UC Institute of Astrophysics .

The image captures the light deflected by the black hole’s powerful gravity, a feat that required the use of eight radio telescopes working in combination, including ALMA and APEX, belonging to the European Southern Observatory (ESO) , from northern Chile . It is the same consortium that in 2019 revealed the first image of a black hole called M87 , in the center of the Messier 87 galaxy, considered the discovery of the year by Science Magazine.

Neil Nagar , an astronomer at the University of Concepción and CATA researcher who participated in both initiatives, together with the astronomer Venkatessh Ramakrishnan , points out that “we are proud to be part of this international collaboration for more than ten years. Three years ago we delivered the first image of a black hole in another galaxy, and now we have achieved a second image, this time in our own galaxy. Although the black hole is a thousand times smaller and less massive, it is also a thousand times closer , ”explains the astronomer, who also directs the Titans Millennium Core .

For his part , Rodrigo Herrera-Camus , astronomer at the University of Concepción and CATA researcher, explains the challenge behind an image like this one. “It is not just one telescope, but multiple telescopes located in different parts of the Earth, including Chile thanks to the ALMA and APEX observatories, which combined form the equivalent of a telescope the size of Earth . And this allows us to have high-resolution images that would otherwise be impossible to achieve.”




Despite the greater proximity of the image of the black hole in the Milky Way compared to the previous image, obtaining it represented a huge challenge that took several more years of work. The scientific team had to develop new and sophisticated tools to explain the movement of gas around Sagittarius A* , which will make it possible to test theories and models about how gas behaves around supermassive black holes.

Ezequiel Treister , astronomer at the Institute of Astrophysics of the Catholic University and deputy director of CATA, explains that this is due to the difference in size between the two black holes , which generates effects: “If in M87 everything happens slower and changes can take days to occur, in Sgr A* everything happens in minutes. In comparison we could say that the hole in the Milky Way is relatively young, it is not still at any time. Instead M87 is an older, more evolved and slower moving object,” he explains.

Astronomers point out that the properties of this image are predicted by Albert Einstein’s Theory of General Relativity. Andrés Escala, Astronomer at the University of Chile and CATA researcher, explains that “For example, the size of the ring coincides very well with these predictions. In addition, its characteristics are similar to the image obtained in M87, despite the fact that the black hole in that galaxy is a thousand times more massive than the black hole in our Milky Way”.

Dr. Neil Nagar adds that they are already working on projects to obtain more images of black holes, which will be key to studying their influence on the formation and evolution of galaxies. “We have two black holes of very different masses. The greater diversity of black holes we record, the more we can learn about their physics,” he concludes.

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