May 10, 2021

Detected for the first time the exact moment in which a black hole is born

Detected for the first time the exact moment in which a black hole is born

A mysterious object shone during the nights of last summer in the sky. It was not detectable to the naked eye, but the most powerful telescopes could identify it and its structure, its shape and its origin have intrigued astronomers ever since. Specifically, since June 17, two twin telescopes in Hawaii found the trace of a spectacular brightness 200 million light years away, in the middle of the constellation of Hercules. They gave it a name: AT2018cow. And a nickname: "The cow." Then he vanished so as not to show signs of life again.

Now, the tenacious research of a team of experts has been able to find an explanation to the phenomenon. For this, the scant information that could be obtained from the brightness has been combined, including X-ray images, with radio wave signals coming from it. The result is spectacular: the phantom signal can respond to the exact moment in which a large star collapsed to become a supermassive body, probably a black hole. That is to say, that trace that was registered in some telescopes could be the first image ever obtained of the birth of a black hole in the cosmos.

The enthusiasm in the scientific community is widespread. Not in vain, black holes are the most intriguing objects of the cosmos and the information we have about them is still very scarce. Although some consider that it could have been produced by the explosion of a neutron star, it is most likely that this powerful and ephemeral emission corresponded to the energy released by the remains of the dying star falling below the horizon of events of the black hole (the border from which nothing can come out, not even light) before losing itself forever in the stomach of the monster.

The unprecedented event is a golden opportunity to better understand the nature of black holes, structures that are part of the great catalog of violent phenomena of the cosmos, and that we know are the result of the death of a star so massive that, in its final collapse, accumulated large amounts of matter in a very small space, so much that its gravitational attraction engulfs everything that falls within its radius of action.

The results of this new research were presented yesterday within the framework of the 233rd meeting of the American Astronomical Association. The main speaker was Raffaella Margutti, from Northwestern University.

The story is long. Shortly after its brightness was identified, the phenomenon captured international attention. Most of the astronomers who came to observe the images thought at first that it was a supernova. But in a short time, the more refined analyzes of the treasured information yielded data that challenged conventional wisdom about these stars.

To begin with, the anomaly detected was extremely large: between ten and a hundred times brighter than that of a supernova. On the other hand, the cycle with which it appeared and disappeared was also extraordinarily fast. Some emitted particles moved at 30,000 kilometers per second (ten percent of the speed of light). In just 16 days, the object had lost almost all of its energetic power. That is, in a cosmos in which things happen very slowly (a star takes billions of years to extinguish), that star had lost its ability to shine in less than 15 days.

Such a strange object deserved a more leisurely look. So measurements were taken by the Keck observatory in Hawaii and the MMT in Arizona. In this way, we could have a closer view of the object to analyze its chemical composition. Large quantities of hydrogen and helium appeared as protagonists.

Finally, Margutti's team came to the study with some of the most powerful cosmological tools: X-ray and hard X-ray analysis (longer wavelength, close to the ultraviolet band, ten times more powerful than the conventional one).

For the study to be successful, it had to be a coincidence (never better said, cosmic). It is known that continuously there are stars that die and turn into black holes. But, in all cases, the amount of matter they absorb and accumulate is so great that it blocks the vision of the telescopes. Therefore, one of these births had never been observed. On this occasion, for unknown reasons, the accumulated matter was ten times smaller. Thus, the scrutinizing eye of the telescopes was able to penetrate to its heart.

The result: the first image of the moment in which a black hole is born. A dying star 200 million light years away.


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