[NTDTV, Beijing time, July 25, 2022]Scientists have discovered the first dormant black hole outside the Milky Way. After a star in a binary system becomes a black hole, how does the system evolve? Scientists now have new clues to the question.
Until now, most black holes discovered by scientists were “active,” meaning they were constantly sucking matter from their surroundings, especially from their companion stars. This process emits a large amount of X-rays that allow scientists to detect the existence of these black holes.
A “dormant” black hole is one that does not draw matter from its surroundings. Scientists think there are also many such black holes, but current technology is difficult to detect. Scientists know that the super black hole at the very center of the Milky Way is a dormant black hole – otherwise our entire solar system will fall towards the center of the Milky Way at an increasing rate!
So, what this study found is the first dormant black hole outside the Milky Way. The black hole is located in the Large Magellanic Cloud not far from the Milky Way.
Astronomers have found that most stars actually have a companion star, that is, most stars are combined in pairs to form a binary system, orbiting each other under the action of gravity. The distance between them can be as far as 10,000 light-years or more, so from the observation data of the telescope, it is not easy to see which star and which star form a binary star system. However, under the strong gravitational force of stars, two stars will always get closer and closer.
Young stars are generally farther away from their companions, and older stars gradually get closer to their companions during their billion-year life cycle. Scientists have found that two things happen at this point.
One is when one star ejects another star when they get too close. Scientists estimate that the sun went through such a situation, kicking a companion star called Nemesis away.
Another scenario is that two stars keep orbiting each other until one of them dies. The researchers believe that the dormant black hole discovered this time came from a star in this situation.
In this binary system, called VFTS 243, researchers first discovered one of the stars, which is about 25 times the mass of the Sun, and later discovered that it has a companion star. It was eventually determined that it was a black hole with a mass about 9 times that of the sun. Their masses are not very different, but the star is 200,000 times the size of the black hole.
The strange thing is that this black hole doesn’t constantly suck material from its companion star, as most systems in this situation do. So the black hole is in a “dormant” state, and it doesn’t emit any X-rays. Why does this happen? This is exactly what scientists want to know more about, and it is also a new clue that can perfect the evolution theory of binary star systems.
Scientists have discovered by exploring gravitational wave signals that, in some cases, two black holes orbiting each other get closer and closer to each other, and finally merge, an event that emits gravitational wave signals. But scientists don’t understand why this happens, and how did two black holes that are very close together form? Didn’t they devour each other long ago? The study believes that the newly discovered dormant black hole is a new clue that can answer this question.
“It’s very likely that they started as two stars in a binary system, and later One by one, they became (dormant) black holes, (and continued to orbit each other).”
The research was published in the journal Nature Astronomy on July 18.
(Transfer from The Epoch Times/Editor-in-charge: Ye Ping)
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