The nearest black gap to Earth isn’t a black gap in any respect. Instead, what scientists thought was a stellar triplet — two stars and a black gap — is definitely a pair of stars caught in a novel stage of evolution.
In May 2020, a staff of astronomers reported that the star system HR 6819 was most likely made up of a brilliant, huge star locked in a good, 40-day orbit with a nonfeeding, invisible black gap plus a second star orbiting farther away. At about 1,000 light-years from Earth, that might make this black gap the closest to us (SN: 5/6/20). But over the next months, different groups analyzed the identical knowledge and got here to a distinct conclusion: The system hosts solely two stars and no black gap.
Now, the unique staff and one of many follow-up groups have joined forces and checked out HR 6819 with extra highly effective telescopes that acquire a distinct sort of information. The new knowledge could make out finer particulars on the sky, permitting the astronomers to definitively see what number of objects are within the system and what sort of objects they’re, the groups report within the March Astronomy & Astrophysics.
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“Ultimately, it was the binary system that best explains everything,” says astronomer Abigail Frost of KU Leuven in Belgium.
Previous observations of HR 6819 confirmed it as a unit, so astronomers couldn’t differentiate the objects within the system nor their plenty. To nail down HR 6819’s true nature, Frost and colleagues turned to the Very Large Telescope Array, a community of 4 interconnected telescopes in Chile that may basically see the separate stars.
“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.
The scientists assume one of many stars is an enormous brilliant blue star that has been siphoning materials from its companion star’s bloated ambiance. That companion star now has little gaseous ambiance left. “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 on the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. El-Badry was not concerned within the new examine, however he prompt in 2021 that HR 6819 is a binary system.
This siphoned star’s core shade and brightness may idiot astronomers trying on the older knowledge into considering it was a younger star with 10 occasions as a lot mass. It initially appeared as if this star was orbiting one thing huge however invisible — a black gap.
Once the researchers unraveled the system’s particulars, they realized this method is a novel one, displaying astronomers a section not seen earlier than amongst methods with huge stars. “It is a missing link in binary star evolution,” says astrophysicist Maxwell Moe of the University of Arizona in Tucson, who was additionally not a part of the brand new examine.
Astronomers for years have seen binary methods the place one star is actively pulling fuel off the opposite, and so they’ve seen methods the place the donor star is only a bare stellar core. But in HR 6819, the donor star has stopped giving mass to the opposite. “It still has a little bit of envelope left but is quickly contracting, evolving to become a remnant core,” Moe says.
Frost and her colleagues are utilizing the Very Large Telescope Array to watch HR 6819 over a 12 months to trace exactly how the celebrities are shifting. “We want to really understand how the individual stars in the system are ticking,” she says. The staff will then use that info in pc simulations of binary star evolution. “[It’s] exciting to now have a system that we can use as kind of a cornerstone to investigate this in more detail,” Frost says.
Even although HR 6819 doesn’t have the closest black gap to Earth, it seems to have one thing extra helpful to astronomers.
