The mystery of a star that seemed too small to exist has been solved – by the detection of another star hiding in the same system.
In 2019, astronomers announced the discovery of an unusual system called KIC 8145411 in which a white dwarf – the dull, compact remnant left behind after certain stars exhaust their nuclear fuel – was orbiting a sun-like star every 450 days. The system is a rare example of a self-lensing binary, where the gravitational heft of the compact white dwarf magnifies the light of its companion star relative to us very slightly, allowing astronomers to measure the dwarf’s mass.
They found that the white dwarf was just a fifth the mass of our sun, which is extremely low for such a star, and was previously only seen in systems where the dwarf tightly orbits another star that saps mass from it. In KIC 8145411, the white dwarf orbits at a distance slightly greater than that between Earth and our sun (1 astronomical unit, or AU), which is too far for the larger star to chip away at the dwarf. Astronomers had just one conclusion: this impossible star shouldn’t exist.
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Now, at the California Institute of Technology and her colleagues have taken another look at the system, using the Palomar Observatory in California, and have a solution. The researchers discovered that the system contains another sun-like star, orbiting the other two far away, at a distance of about 700 AU. Factoring this new star into the calculations, the team determined the mass of the white dwarf to be more agreeable, at about half that of our sun. “It’s no longer impossible,” says Yamaguchi.
While three-body systems are common in the universe, the discovery of the hidden star in KIC 8145411 suggests that other supposed binary systems may also host additional, unseen stars, confusing some of our calculations for working out stellar masses. “This situation where you have two bright stars but you think it’s one is probably not that uncommon,” says Yamaguchi.
Any planet in a system with three stars would potentially have wild and unusual seasons as it travelled around its orbit. Unfortunately, however, such worlds are unlikely to be found in KIC 8145411, as they would have been incinerated when the white dwarf originally formed. “If there was a planet, it probably would have gotten destroyed,” says Yamaguchi.
arXiv
