An artist’s impression of what the binary star system VFTS 243, containing a black hole and a large luminous star orbiting each other, would look like if we were to observe it from close range. (REUTERS)
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WASHINGTON — Astronomers have discovered in what they call the cosmic “needle in a haystack” a galaxy adjacent to our own Milky Way, a black hole that is not only classified as dormant, but appears to have been born without the explosion of a dying star.
On Monday, researchers said this one is different from all other known black holes in that it is “X-ray quiet” — not emitting powerful X-rays that indicate nearby material is being absorbed by its strong gravitational pull — and that it was not born in a stellar explosion. called a supernova.
Black holes are extremely dense objects with such powerful gravity that not even light can escape them.
This one, with a mass of at least nine times that of our Sun, was discovered in the Tarantula Nebula region of the Large Magellanic Cloud galaxy and is located about 160,000 light-years from Earth. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).
An extremely bright and hot blue star with about 25 times the mass of the Sun orbits this black hole in a stellar marriage. This so-called binary system is called VFTS 243. The researchers believe that the companion star will eventually also become a black hole and may merge with another.
Sleeping black holes, which are considered fairly common, are difficult to detect because they interact very little with their environment. Numerous previously proposed candidates have been refuted by further study, including by members of the team that discovered this candidate.
“The challenge is to find these objects,” said Tomer Shenar, an astronomy researcher at the University of Amsterdam and lead author of the study, published in the journal Nature Astronomy. “We found a needle in a haystack.”
“This is the first object of its kind discovered after astronomers have been searching for it for decades,” said astronomer and study co-author Karim El-Badri of the Harvard and Smithsonian Center for Astrophysics.
It is the first object of its kind to be discovered after astronomers have been looking for it for decades.
– Karim El-Badri, astronomer and study co-author
The researchers used six years of observations at the European Southern Observatory’s Very Large Telescope in Chile.
There are different categories of black holes. The smallest, like the one recently discovered, are so-called stellar-mass black holes, formed from the collapse of massive individual stars at the end of their life cycles. There are also intermediate mass black holes, as well as huge supermassive black holes at the center of most galaxies.
“Black holes are inherently dark objects. They don’t emit any light. Therefore, to detect a black hole, we usually look at binary systems in which we see one luminous star moving around a second, undetected object, ”he said. study co-author Julia Bodensteiner, research fellow at the European Southern Observatory in Munich.
It is usually assumed that the collapse of massive stars into black holes is associated with a powerful supernova explosion. In this case, a star with about 20 times the mass of our Sun, in its death throes, ejected some of its material into space, and then collapsed on itself without an explosion.
The shape of its orbit with a companion indicates the absence of an explosion.
“The system’s orbit is almost perfectly circular,” Shenar said.
Shenar added that if a supernova were to erupt, the force of the explosion would throw the newly formed black hole in a random direction and result in an elliptical, rather than circular, orbit.
Black holes can be relentlessly voracious, devouring any material — gas, dust, and stars — that wanders within their gravitational pull.
“Black holes can only be relentlessly voracious if there is something close enough to them that they can devour. We usually detect them if they receive material from a companion star, a process we call accretion,” Bodensteiner said.
Shenar added: “In so-called sleeper black hole systems, the companion is far enough away that material doesn’t build up around the black hole, heats up and emits X-rays. Instead, it was immediately consumed by the black hole.”
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