A new black hole discovered, closest to Earth observed so far
Since it is a dormant black hole, it could be identified by the variations it induces in the orbit of the star gravitating around it
What if we have a dormant black hole behind our house? That’s more or less — given due astronomical proportions — what Kareem El-Badry, a Harvard-Smithsonian Center for Astrophysics researcher in the United States, and his colleagues have just discovered. The huge astronomical object, as explained in the article published in the journal Monthly Notices of the Royal Astronomical Society on Nov. 2, is the closest to us discovered so far: it is located about 1,600 light-years from Earth, within the constellation Ophiuchus, has a mass about ten times that of the Sun, and has been nicknamed Gaia BH1.
Black holes are regions of space with extraordinary properties: their density is such that they generate an enormous gravitational field that traps even light, making them invisible except through interactions with surrounding celestial bodies. “Active” black holes are detected through the high levels of X-rays they emit as they consume the matter that makes up the star orbiting them. In the case of dormant black holes, however, this is impossible since they do not actively consume weight and, consequently, do not emit X-rays. This characteristic makes them even “blacker” in the eyes of our detection instruments, which are even more challenging to detect.
How is it possible to see a dormant black hole
If it is already complex to “see” active black holes (astronomers from the Event horizon telescope consortium managed to reconstruct an image of them for the first time in 2019), even more, difficult is to unearth their dormant relatives. The discovery cost four years of work for the research team, which succeeded by spotting slight irregularities in the star’s orbit gravitating around Gaia BH1. These anomalies, due precisely to the gravity exerted by the subsequently characterized black hole, were observed by analyzing data from the European Space Agency’s Gaia probe, which continually detects the motions and properties of millions of stars within the Milky Way. Next, El-Badry and his colleagues more precisely measured the velocity of the star orbiting Gaia BH1 using the Gemini North telescope located on the Hawaiian Islands, providing data that later proved crucial to the identification and characterization of the black hole.
“Our follow-up observations on Gemini confirmed beyond reasonable doubt that the binary [the system composed of the newly discovered black hole and the star orbiting it, ed.] contains a normal star and at least one inactive black hole,” said the study’s first author. “We could not find a plausible astrophysical scenario that could explain the observed orbit of the system that does not involve at least one black hole.”
We still have much to learn.
ont-weight: 400;”>A black hole typically arises from the implosion of a star with a sufficiently large mass. In this case, however, the origin of Gaia BH1 needs to be clarified. According to the theories we currently know, the star that would have originated it should have had a mass about 20 times that of the Sun. This should have somehow altered the star’s behavior that still gravitates around it, which instead seems to behave in an entirely predictable way. These observations “also leave a mystery to be solved,” says Martin Still, NSF Gemini program officer: despite its shared history with its exotic neighbor, why is the companion star of this binary system so typical? El-Badry concludes that there are still many open questions about how this system could have formed and how many black holes remain to be discovered.