Astronomers have presented the first image of a supermassive black hole in the center of our galaxy. The image obtained is the result of a long-term analysis of data collected by a global network of radio telescopes called the Event Horizon Telescope (EHT). Polish astronomers are involved in the discovery. The results were presented by ESO and EHT.
On May 12, 2022, simultaneous press conferences were held at the headquarters of the European Southern Observatory (ESO) and in several other parts of the world. Scientists have presented groundbreaking observations of the Milky Way Center using the Event Horizon Telescope (EHT). In the center of our galaxy is a picture of a supermassive black hole. It shows the shadow of a black hole and a bright ring right next to the black hole’s event horizon. The size of the shadow of the black hole is an arc of about 52 microseconds across the sky. This is the size of a donkey on the surface of the moon.
Not surprisingly, there is a supermassive black hole in the center of the Milky Way. Astronomers have long suspected its existence. In fact, most galaxies are believed to have supermassive black holes at their centers. However, the strongest evidence of a black hole at the site of the Sagittarius A * radio source has so far been observations of the orbits of nearby stars over a very long period of time (up to 30 years). These actions clearly show that at this point there is an invisible object with a mass four million times that of the sun (that is, it must be a black hole).
The images shown today are the first direct visual confirmation of the existence of the black hole Sgr A *. Scientists say they are amazed at how well the ring size matches Albert Einstein’s predictions about general relativity.
The figure shows the location of Sagittarius A *, a supermassive black hole in the center of the galaxy, where the ALMA radio telescope network looks at the Milky Way. The box shows a description of the Sagittarius A * source obtained by the Event Horizon Telescope (EHT). ALMA is the most sensitive of all EHT network observatories. Source: ESO / José Francisco Salgado (josefrancisco.org), EHT Collaboration.
A more difficult task than before
The presented image of Sagittarius A * black hole is not the first picture of the black hole we have. In 2019, the Event Horizon Telescope’s observations of the Messier 87 galaxy were shown. The black hole M87 * is far from our galaxy, so why did it take so long to get results for Sgr A *?
Both objects have a similar angular size in the sky, but the M87 * has a more stable image and the Sgr A * shows more variability around it. In both cases, the velocities of the gas circulating near the event horizon are the same (close to the speed of light), but it takes days and even weeks (because it is larger) to orbit M87 *, and it only takes a few minutes. Complete the orbit around Sgr A *. As a result, the luminosity and gas structures around the black hole in our galaxy are changing much faster, and scientists have had to develop methods to explain this in order to obtain images.
Comparison of black holes
The masses and radii of black holes are directly proportional to each other. If a black hole is a thousand times bigger than another, it will be a thousand times bigger. However, in the sky, both M87 * and Sgr A * have similar angular dimensions, although the former is about 1,600 times larger than the latter. This is due to the difference in distances to these objects. The black hole in the Milky Way is 27,000 light-years, and the black hole in the Messier 87 galaxy is 55 million light-years.
However, although the types of the two galaxies are different and the masses of the two black holes are different in size, the objects are similar. They look very similar at the edges of black holes, and this shows that the general relativity governs these objects closely, and that any difference we see in the distance must be due to differences in the matter surrounding the black holes.
Scientists now have images of two supermassive black holes. One is at the upper end of the mass and measurement range of such objects (M87 *), and the other is at the lower end of supermassive black holes (Sgr A *). This will make it possible to study the differences between them and better test the behavior of gravity in such extreme environments.
In the photo below you can see the comparison of the first images of black holes.
Comparison of images of two black holes. M87 * left and Sgr A * right. Source: EHT Cooperation.
In turn, the next illustration shows the dimensions of both objects in relation to different scales in the solar system, such as Pluto’s orbit, Mercury’s orbit, the diameter of the Sun, or the current position of Voyager 1 – the spacecraft sent from the farthest Earth.
Comparison of the dimensions of two black holes: M87 * and Sgr A *. Source: EHT cooperation (confirmation: Lia Medeiros, xkcd).
International effort with the participation of Poland
The discovery was made possible by the work of a large international team of scientists. More than 300 scientists from 80 institutes from around the world participated. The observations were made in April 2017 and covered the following radio telescopes: Atacama Large Millimeter / submillimeter Array (ALMA), Atacama Pathfinder Experiment (APEX), IRAM 30 meter Telescope, James Clerk Maxwell Telescope (JCMT), Large Millimeter Telescope Alfonso Serra ( ), Submillimeter Array (SMA), UArizona Submillimeter Telescope (SMT), South Pole Telescope (SPT). The Greenland Telescope (GLT), the North Extended Millimeter Array (NOEMA) and the 12-meter UArizona Telescope at Kitt Peak were later added to the EHT network.
The world map shows radio observatories that are part of the Event Horizon Telescope (EHT) network used to depict the central black hole of the Milky Way, known as Sagittarius A *. The telescopes, highlighted in yellow, were part of the EHT network in 2017 when observing the Sagittarius A * source. The list includes: Atacama Large Millimeter / submillimeter Array (ALMA), Atacama Pathfinder Experiment (APEX), IRAM 30m telescope, James Clark Maxwell Telescope (JCMT), Large Millimeter Telescope (LMT), Submillimeter Array (SMA), Submillimetere Teles and the South Pole Telescope (SPT). After 2018, three blue-marked telescopes were added to the EHT project: the Greenland Telescope, the Northern Extended Millimeter Array (NOEMA) in France, and the 12-meter UA Arizona ARO Telescope at Kitt Peak. Source: ESO / M. Kornmesser.
It should be added that Europe has made an important contribution to the discovery. many European scientists believe that some of the telescopes mentioned above are European instruments or European instruments (even if they are located on other continents). One of the supercomputers used to combine the data collected by EHT operates in Europe – it is located at the Max Planck Radio Astronomical Institute in Germany. Europe has also significantly funded research through grants from the European Research Council and the Max Planck Society in Germany.
The Poles could not miss this important discovery. There are two of them in the EHT team: prof. Dr. Monica Mościbrodzka from Radboud University in Nijmegen (Netherlands) and Dr. Max Planck Institute of Radio Astronomy (Germany) in Bonn. Maciek Wielgus. Professor Mościbrodzka made a significant contribution to the theory of publications, and Dr. Wielgus made a significant contribution to data processing – he was the first author of one of the publications on light curves Sgr A *.
The study was published in a series of articles in a special issue of The Astrophysical Journal Letters. Thanks to the images of two supermassive black holes at the disposal of scientists, they are able to study the differences between them and test the behavior of gravity in extreme conditions better than before.
A mixture of images from the radio observatories that make up the Event Horizon Telescope (EHT) network is used to depict the central black hole of the Milky Way, known as Sagittarius A *. Observatories include: Atacama Large Millimeter / submillimeter Array (ALMA), Atacama Pathfinder Experiment (APEX), 30 meter IRAM telescope, James Clark Maxwell Telescope (JCMT), Large Millimeter Telescope (LMT), Submillimeter Array (SMA), Submillimetere Telecopes and the South Pole Telescope (SPT).
In the background, somewhat transparent telescopes represent three telescopes that have been added to the EHT partnership since 2018: the Greenland Telescope, the Northern Extended Millimeter Array (NOEMA) in France, and the ARO 12-meter Telescope in Kitt Peak. These telescopes were added to the network in 2017 after a study of the source Sagittarius A *.
Source: ESO / M. Kornmesser. Pictures of individual telescopes:
LMT: INAOE Archives
GLT: N. Patel
JCMT: EAO-W. Montgomery
SMT: D. Harvey
30 m: N. Billot
SMA: SR Schimpf
Kitt Pik: Wikipedia
Milky Way: N. Risinger (skysurvey.org)
ESO press release: Astronomers have presented the first image of a black hole in the center of our galaxy
EHT Press Release:
Author: Krzysztof Czart
Source: ESO / EHT
This is the first image of Sgr A * of a supermassive black hole in the center of our galaxy. This is the first direct visual evidence of the existence of this black hole. The image was obtained by Event Horizon Telescope (EHT), a network of eight radio observatories around the planet. Source: EHT Cooperation.