3/23/2023 0 Comments Closest black hole to earth“It is a missing link in binary star evolution,” says astrophysicist Maxwell Moe of the University of Arizona in Tucson, who was also not part of the new study.Īstronomers for years have seen binary systems where one star is actively pulling gas off the other, and they’ve seen systems where the donor star is just a naked stellar core. Once the researchers unraveled the system’s details, they realized this system is a unique one, showing astronomers a phase not seen before among systems with massive stars. It originally appeared as though this star was orbiting something massive but invisible - a black hole. This siphoned star’s core color and brightness could fool astronomers looking at the older data into thinking it was a young star with 10 times as much mass. El-Badry was not involved in the new study, but he suggested in 2021 that HR 6819 is a binary system. “It’s already gone through its main life, but because the outside has been stripped off, and you only see the exposed core, it has similar temperature and luminosity and radius to a young star,” says Kareem El-Badry, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. That companion star now has little gaseous atmosphere left. The scientists think one of the stars is a massive bright blue star that has been siphoning material from its companion star’s bloated atmosphere. “It allowed us to disentangle that original signal definitively, which is really important to determine how many stars were in it, and whether one of them was a black hole,” Frost says. To nail down HR 6819’s true nature, Frost and colleagues turned to the Very Large Telescope Array, a network of four interconnected telescopes in Chile that can essentially see the separate stars. Previous observations of HR 6819 showed it as a unit, so astronomers couldn’t differentiate the objects in the system nor their masses. “Ultimately, it was the binary system that best explains everything,” says astronomer Abigail Frost of KU Leuven in Belgium. The new data can make out finer details on the sky, allowing the astronomers to definitively see how many objects are in the system and what type of objects they are, the teams report in the March Astronomy & Astrophysics. Now, the original team and one of the follow-up teams have joined forces and looked at HR 6819 with more powerful telescopes that collect a different type of data. But over the following months, other teams analyzed the same data and came to a different conclusion: The system hosts only two stars and no black hole. At about 1,000 light-years from Earth, that would make this black hole the nearest to us ( SN: 5/6/20). In May 2020, a team of astronomers reported that the star system HR 6819 was probably made up of a bright, massive star locked in a tight, 40-day orbit with a nonfeeding, invisible black hole plus a second star orbiting farther away. Instead, what scientists thought was a stellar triplet - two stars and a black hole - is actually a pair of stars caught in a unique stage of evolution. The nearest black hole to Earth isn’t a black hole at all.
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