This image is a long-awaited glimpse of the massive object sitting at the center of our galaxy. Scientists had previously observed stars in orbit around an invisible, compact and very massive object in the center of the Milky Way. This strongly suggested that this object – known as Sagittarius A * (Sgr A *) – was a black hole, and today’s image provides the first direct visual proof of this.
Although it is not possible to see the black hole itself because it is completely dark, the glowing gas that surrounds it reveals a characteristic signature: a dark central region (called a “shadow”) surrounded by a structure that is radiant in the form of a ring. The new image captures light that is deflected by the powerful force of the black hole, which is four million times more massive than our sun.
” We were surprised at how well the size of the ring matched the predictions from Einstein’s general theory of relativity said EHT project scientist Geoffrey Bower of the Department of Astronomy and Astrophysics at the Academia Sinica in Taipei. ” These unprecedented observations have dramatically improved our understanding of what is happening at the center of our galaxy, and provide new insights into how these giant black holes interact with their surroundings. The results of the EHT team are published today in a special issue of the journal The Astrophysical Journal Letters.
With the black hole located about 27,000 light-years from Earth, it appears to be the size of a donut on the Moon in the sky. To get a picture of it, the team created the powerful EHT, which connected eight existing radio observatories across the planet to form a single “earth-sized” virtual telescope. EHT observed Sgr A * for several nights and collected data for several hours in a row, much like a long exposure time on a camera.
IRAM’s 30 meter telescope is the world’s most sensitive single-bowl telescope in the high frequency range that EHT uses for its observations. Together with the South Pole Telescope, it gave the longest baseline and thus the sharpest images, and thus contributed decisively to the high spatial resolution of the images of Sgr A *.
This progress follows the 2019 publication of the EHT collaboration of the first image of a black hole, called M87 *, at the center of the more distant galaxy Messier 87.
The two black holes are remarkably similar, although in our galaxy it is more than a thousand times smaller and less massive than the M87 *. ” We have two completely different types of galaxies and two very different masses of black holes, but near the edge of these black holes they look surprisingly similar. says Sera Markoff, Co-Chair of the EHT Scientific Council and Professor of Theoretical Astrophysics at the University of Amsterdam, The Netherlands. ” This tells us that the general theory of relativity controls these objects closely, and that any difference we see further away must be due to inequalities in the matter around the black holes. »
This result was significantly more difficult than for M87 *, although Sgr A * is much closer to us. EHT Researcher Chi-kwan (“CK”) Chan from the Steward Observatory and the Department of Astronomy and the Department of Computer Science at the University of Arizona, USA, Explain: ” Gas near black holes moves at the same speed – almost as fast as light – around Sgr A * and M87 *. But even though it takes days or even weeks to circle the large M87 *, it only takes minutes to make it around the much smaller Sgr A *. This means that the brightness and gas configuration around Sgr A * changed rapidly as the EHT collaboration observed it – much like trying to take a clear picture of a puppy chasing its tail. »
Researchers had to develop sophisticated new tools that take into account the gas movement around Sgr A *. While M87 * was a lighter and more stable target whose images almost all looked alike, this was not the case for Sgr A *. The image of Sgr A *’s black hole is an average of the various snapshots drawn by the team, and finally reveals for the first time the giant lurking in the center of our galaxy.
This effort was made possible by the ingenuity of more than 300 researchers from 80 institutes around the world who make up the EHT collaboration. In addition to developing complex tools to meet the imaging challenges of Sgr A *, the team worked very rigorously for five years, using supercomputers to collect and analyze their data while compiling a library that is an unprecedented number of simulated black holes for to compare with observations.
Researchers are particularly excited to finally have images of two very different sized black holes so they can understand how they compare and contrast. They also began using this new data to test theories and models of how gas behaves around supermassive black holes. This process is not yet fully understood, but it is thought to play a key role in the formation and evolution of galaxies.
” We can now study the differences between these two supermassive black holes to gain valuable new clues as to how this important process works. said Keiichi Asada, EHT Researcher, Department of Astronomy and Astrophysics, Academia Sinica, Taipei. ” We have images of two black holes – one at the large, wide end and the other at the small end of supermassive black holes in the universe – allowing us to go much further into the universe than ever before. analysis of the behavior of gravity in these extreme environments. »
EHT progress continues: A major observation campaign in March 2022 included more telescopes than ever before. The continued expansion of the EHT network and significant technology upgrades will allow scientists to share even more impressive images and films of black holes in the near future.
By joining the EHT network in 2018 and making its first observations in 2021, IRAM’s second observatory, Noema, has already given EHT a decisive boost in terms of sensitivity, image dynamics and spatial resolution. However, the continued development of advanced reception technologies for Noema and IRAM’s 30 meter telescope will enable the EHT collaboration to make timelapses with even finer details. Both facilities will be the key to the EHT collaboration to understand the physics of massive black holes, and in particular Sgr A *.
To know more : read this article from CNRS Le Journal.
© H.Falcke, A.Schut, R.Fraga-Encinas, Radboud University, Fiks Films