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Researchers Discover Dormant Black Hole Beyond Milky Way

A stellar-mass black hole has been discovered in the Large Magellanic Cloud, one of the neighbors of the Milky Way, by a group of international specialists recognized for disproving many black hole findings.

Researchers Discover Dormant Black Hole Beyond Milky Way.
This artist’s impression shows what the binary system VFTS 243 might look like if we were observing it up close. The system, which is located in the Tarantula Nebula in the Large Magellanic Cloud, is composed of a hot, blue star with 25 times the Sun’s mass and a black hole, which is at least nine times the mass of the Sun. The sizes of the two binary components are not to scale: in reality, the blue star is about 200 000 times larger than the black hole. Note that the “lensing” effect around the black hole is shown for illustration purposes only, to make this dark object more noticeable in the image. The inclination of the system means that, when looking at it from Earth, we cannot observe the black hole eclipsing the star. Image Credit: European Southern Observatory/L. Calçada.

For the first time, our team got together to report on a black hole discovery, instead of rejecting one.

Tomer Shenar, Study Leader, Institute of Astronomy, KU Leuven and University of Amsterdam

Scientists also discovered that the star that created the black hole disappeared without leaving any traces of a massive explosion. The finding was made possible by six years of observations done with the Very Large Telescope (VLT) of the European Southern Observatory (ESO).

We identified a ‘needle in a haystack,’” said Shenar, a Marie-Curie Fellow at Amsterdam University in the Netherlands who began the research at KU Leuven in Belgium. This is the first “dormant” stellar-mass black hole to be unmistakably discovered beyond the galaxy, according to the research team, despite numerous hypotheses for such black holes having been suggested.

When large stars near the end of their lives collide with one another due to gravity, stellar-mass black holes are created. This approach leaves behind a black hole in orbit with a bright companion star in a binary, a system of two stars rotating around one another. If the black hole does not generate significant amounts of X-Ray radiation, which is how these black holes are normally discovered, then it is said to be “dormant.”

It is incredible that we hardly know of any dormant black holes, given how common astronomers believe them to be,” says co-author Pablo Marchant of KU Leuven. The newly discovered black hole circles a bright, blue star that is 25 times the mass of the Sun and is at least nine times as massive as the Sun.

Black holes that are dormant are especially difficult to locate since they do not interact with their environment.

For more than two years now, we have been looking for such black-hole-binary systems. I was very excited when I heard about VFTS 243, which in my opinion is the most convincing candidate reported to date.

Julia Bodensteiner, Study Co-Author and Research Fellow, European Southern Observatory

Nearly 1000 massive stars in the Tarantula Nebula area of the Large Magellanic Cloud were combed by the cooperation in search of potential black hole partners in order to locate VFTS 243. It is quite difficult to determine whether these companions are black holes since there are so many other potential explanations.

Shenar notes, “As a researcher who has debunked potential black holes in recent years, I was extremely skeptical regarding this discovery.” Co-author Kareem El-Badry, who Shenar refers to as the “black hole destroyer” who works at the Center for Astrophysics | Harvard & Smithsonian in the United States, expressed the same doubt.

When Tomer asked me to double check his findings, I had my doubts. But I could not find a plausible explanation for the data that did not involve a black hole,” says El-Badry.

The finding also gives the scientists a novel perspective on the procedures that go along with black hole development. Although it is thought by astronomers that a stellar-mass black hole develops when the center of a dying big star collapses, it is still unknown whether or not this is coupled with a violent supernova explosion.

The star that formed the black hole in VFTS 243 appears to have collapsed entirely, with no sign of a previous explosion. Evidence for this ‘direct-collapse’ scenario has been emerging recently, but our study arguably provides one of the most direct indications. This has enormous implications for the origin of black-hole mergers in the cosmos.

Tomer Shenar, Study Leader, Institute of Astronomy, KU Leuven and University of Amsterdam

The Fiber Large Array Multi Element Spectrograph (FLAMES) instrument on ESO’s VLT observed the Tarantula Nebula for six years in order to find the black hole in VFTS 243.

Despite the nickname “black hole police,” the team actively encourages scrutiny and hopes that the work they have done, which was recently published in Nature Astronomy, will lead to the identification of additional stellar-mass black holes orbiting massive stars, of which thousands are thought to exist in the Milky Way and the Magellanic Clouds.

Of course I expect others in the field to pore over our analysis carefully, and to try to cook up alternative models. It's a very exciting project to be involved in,” concludes El-Badry.

Journal Reference:

Shenar, T., et al. (2022) An X-ray-quiet black hole born with a negligible kick in a massive binary within the Large Magellanic Cloud. Nature Astronomy.


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