BLACK HOLE. Located in our galaxy, a black hole has been discovered thanks to the Hubble Space Telescope. It is a rare type of black hole whose origin is still poorly understood by astronomers.
[Updated May 25, 2023 4:25 PM] Although less powerful than its successor James Webb, the Hubble Space Telescope has not said its last word. It is thanks to its instruments that a team of researchers from Maryland was able to flush out a still unknown black hole in the globular cluster of Messier 4, a very dense area of ??stars located in the Milky Way. This black hole, the presence of which is strongly suspected by NASA, has two particularities. For one thing, it’s only 6,000 light-years from Earth, which on an astronomical scale is pretty close. On the other hand, it is an unusual black hole by its size. Estimated at around 800 solar masses, this black hole is of an intermediate type which places it between the small stellar black holes and the largest known, the famous supermassive black holes.
Spotting these stellar objects is extremely difficult. Indeed, by nature, black holes suck up everything that passes nearby, including light. Therefore, it is very complicated to photograph them. So, to unearth this black hole, NASA implemented a commonly used strategy. She observed the Messier 4 cluster and the stars that compose it for 12 years. It was the movements of the stars located in the gravitational field of the black hole that made it possible to detect its presence.
The very nature of the black hole makes its observation difficult. To summarize: black holes are astronomical objects that exist in Einstein’s theory of general relativity, and in the theory of black holes developed by successive scientists, from Wheeler to Stephen Hawking. They are infinitely massive objects in the universe. Their mass is so great that absolutely nothing can escape their attraction, not even light. Hence the difficulty in capturing them on a photo. If their existence had not been 100% confirmed, the existence of black holes was already suspected in many places in the universe, including in the center of our galaxy.
Intermediate black holes are a recently discovered and rarely observed category. We do not yet know all the secrets of their formation, but scientists are advancing some hypotheses on the subject. Intermediate black holes may have arisen by aggregation of smaller black holes. They could also have formed from primordial black holes whose birth dates back to the first moments of the Universe. The discovery of a potential intermediate black hole near the Sun in the globular cluster Messier 4 could help us learn more about these objects which are the subject of controversy within the scientific community.
A black hole is a region of space where matter is so dense that gravity prevents light from escaping. It is precisely for this reason that they are invisible and called “black holes”. A black hole is delimited by a “horizon” which corresponds to the limit from which it would have to reach a speed greater than that of light to escape from it. In other words, from this limit, even the light can no longer be extracted from the black hole.
A supermassive black hole is a category of black holes, along with stellar black holes, primordial black holes and intermediate black holes. Supermassive black holes are characterized by a mass that can be between several million and up to billions of times the mass of the Sun. They are therefore behemoths among black holes.
In 2019, the first photo of a black hole was published. It was M87 located in the galaxy Messier 87. This first black hole image (below) allowed us to validate the hypothesis of their existence since the latter had never been proven. In the words of the CNRS, one can see “a ring structure with a dark, circular central region”. This central area is the black hole itself, which stands out against the bright background. An image that corresponds exactly to what Einstein’s theory of general relativity predicts. “The orange structure corresponds to the superheated matter around the black hole” continues the CNRS site.
The image above made it possible to illustrate a certain number of characteristics that we already knew about this black hole. For example, we knew that its mass was approximately 6.5 billion times that of our Sun, a record for this type of object. Another big tidbit: the black hole itself measures 38 billion kilometers, or 250 astronomical-units, the distance between the Sun and Earth. The disk of gas surrounding it is about 100 times larger. Dizzying figures, in front of an image difficult to decipher for novices.
The reactions to this first black hole image taken in 2019 were unanimous, in the specialized press but also in the general media and on the Internet. “The door to the Universe” headlined, for example, the Catalan newspaper Ara. “Dizzy !” for Telegram. And even in the press, we allowed ourselves some diversions: “What does the Brexit of space look like?” asked Metro on April 11, 2019. Scientists were then moved by the progress represented by this image. “We have succeeded in transforming a mathematical tool into a physical object that can be tested, observed and measured” explained one of the speakers during the press conference where the image was unveiled.
A second image had also been released. This shows a much larger shot of the black hole. If the “hole” itself appears much less clearly on this photo, we see on the other hand a much more impressive image of the gas and the superheated matter in the center of the galaxy M87. Taken by the Chandra telescope, it is also much more dizzying: our solar system could fit in the black dot in the center of the box in the photo.
In 2022, the Event Horizon Telescope produced a second photo of a black hole. This time, it is Sagittarius A*, the supermassive black hole of our Galaxy, which has been captured. However, between the two black holes, the resemblance is striking.
“The result is perhaps a little disappointing because the two images are very similar,” analyzed Frédéric Gueth, deputy director of the Institute of Millimetric Radio Astronomy (IRAM), at Le Monde “But, in reality, it’s a very interesting result. This result indicates, on the one hand, that the first photo is not the result of chance or an error, since the two shots look alike. Secondly, these two similar images make it possible to verify Einstein’s theory of general relativity since we find the same structures on two black holes located in very distant places.
The processes that lead to the formation of a black hole remain largely obscure to the scientific community although a number of theories exist. Depending on the nature of the black hole, the mechanisms implemented are not the same.
Stellar black holes result from the death of a star massive enough to collapse in on itself. When a star dies, it ends up contracting on itself and going out. But if the latter is very massive, the remaining mass concentrates in an infinitely small and dense point which is called “the singularity”. This point generates a force of gravity such that even light cannot escape.
Supermassive black holes like Sagittarius A* or M87, the two black holes having been photographed in 2019 and 2022, raise more questions for scientists who do not yet know their formation mechanism. However, it is possible that these black holes are the result of the merger of several stellar black holes.