US, WASHINGTON (ORDO NEWS) — Astronomers have witnessed a cosmic tragedy: the gradual destruction of a star by a supermassive black hole. The luminary was once a giant, now it has become a dwarf, and over time, a stump the size of a planet should remain from it.
True, the scientists did not see this sad sight, but just flashes of X-ray radiation recorded by the Chandra and XMM-Newton telescopes . These bursts come from the central black hole of the galaxy GSN 069. The predator is located at a distance of 250 million light years from Earth and has a mass of 400 thousand suns.
X-rays from black holes are far from new . It is known that it is emitted by a cloud of red-hot substance, gradually settling on this space monster. But in this case, astronomers were interested in the regularity of bursts: they are repeated every nine hours.
Andrew King ( Andrew King ) from the University of Leicester explained to his colleagues that they see in a scientific article published in the journal Monthly Notices of the Royal Astronomical Society. True, its version may not be the only possible one, but the expert offers an easy way to check it.
Life and death of stars
So, according to the astrophysicist, this was the case. Once upon a time there was a star. And, as usual, in its core, hydrogen in the course of thermonuclear reactions was transformed into other chemical elements. But hydrogen in the core, like everything else, ends sooner or later.
What usually happens to the luminaries in this sad moment? New processes are starting. This is, firstly, the conversion of hydrogen to helium in the outer layers of the star, and secondly, the conversion of helium in the core into heavier elements. From the emitted radiation, the star swells, turning into a red giant. But even this thermonuclear fuel is gradually coming to an end. What then?
Stars weighing more than ten suns end their lives in supernova explosions, but now it’s not about them. But the star of a more modest mass dies otherwise. Its outer layers are scattered in space , and the core turns into a white dwarf. The latter is a red-hot and very dense asterisk, comparable in mass with the Sun, and in size with the Earth. No thermonuclear reactions take place in it, and it glows simply because it is very hot (but gradually the white dwarf flashes its energy and cools down).
When something went wrong
So everything happens if nothing prevents the star from dying. But this time it was different. Because the nameless red giant in the galaxy GSN 069 made a mistake. He was too close to her central black hole.
Typically, in such situations, the gravity of a supermassive monster immediately tears the unfortunate body to pieces . And so it would be if the predator was more massive. But in this case, its small mass by the standards of supermassive black holes played into the victim’s hands (if slow death can be considered more preferable than fast).
Gravity of a black hole tore off the outer layers from an unlucky guest and, ahead of time, without letting it burn out, turned it into a white dwarf. And this dwarf now revolves around its tormentor in an elongated orbit, making a complete revolution in those very nine hours.
But the torment does not end there. The black hole continues to pull matter from the white dwarf. Since it is much lighter and much denser than the original red giant, now this process is much slower. By the way, according to King’s calculations, the mentioned white dwarf should be five times lighter than the Sun.
Every nine hours, to his horror, he passes the point of orbit closest to his insatiable cartridge (at a distance of no more than 15 black hole radii). Then the latter tears off a particularly large piece from its victim. The fall of this substance into a black hole causes the same x-ray bursts with which this terrible story began.
What will happen next? As the white dwarf is gradually eaten by a black hole, it becomes easier. Because of this, its orbit becomes less and less elongated, gradually approaching a circular one. Its diameter also grows (gravitational waves also play a role in this process, gradually taking energy from the system).
As the white dwarf moves farther and farther away from the black hole, it suffers less and less from its gravity. But he will never go far enough so as not to lose any substance.
“He will try his best to leave, but there is no escape for him. The black hole will eat him more slowly, but he will never stop,” King paints a picture worthy of a namesake writer. “In principle, this mass loss will continue until even after the white dwarf shrinks to the mass of Jupiter in about a trillion years. For the Universe, this will be an amazingly slow and complex way to create a planet! ”
However, the universe is less than 15 billion years old, and making a forecast for a trillion years is somewhat bold. During this period, much can happen with the long-suffering system, as with the entire parent galaxy.
But what if everything is different?
However, we will not get carried away. The only thing that is undoubted in this whole story is periodic X-ray flashes. Maybe they have a completely different nature, and all the horror described above is a figment of the scientist’s imagination?
King offers an easy way to verify this. He calculated that the orbit of a white dwarf should change orientation (precess), returning to its previous position every two days. This should be reflected in x-ray flares, and long enough observations would help to capture this effect. Then it will become clear whether this slowly dying star exists in reality.
Universe as an arena of violence
King suggests that such processes should occur even more often than the rapid destruction of stars by black holes, which has already been observed many times. King even believes that such “eating” of stars can be one of the main ways of growing black holes weighing from the gloomy inhabitant of GSN 069.
It’s just that a slow death of a star is more difficult to notice than a fast death. There are several reasons for this.
First, in order to see periodic flashes of radiation, the telescope must observe the same region of the sky for several periods. But there are few X-ray observatories, and their time, as they say, is snapped up. If the white dwarf needed one turn, not nine hours, but nine days or even more months, most likely, we would never know about him.
Secondly, the slow meal of a space gourmet (or a sadist?) Creates much less x-rays than a one-time feast, when the whole star is torn to pieces and absorbed. Therefore, the distances from which we can notice the first process are not so great by intergalactic standards.
Finally, even this radiation remains somewhat discernible for about a couple of millennia. Then the white dwarf moves away from the black hole so much that the portions torn off by the predator are very small. Therefore, the x-ray radiation associated with their fall becomes indistinguishable for terrestrial telescopes.
So, we were simply lucky that something similar happened and came into the view of our observatories in the present instant (on the scale of the Universe) when they observed this particular part of the sky. And the white dwarf was lucky that someone found out about his tragedy. Perhaps a talented playwright will one day tell this story (what is not an analogue of the plot about Prometheus and his torture?).
Contact us: [email protected]