Astronomers on Maunakea have discovered a planet that has seemingly survived some of the universe’s most extreme conditions.
In a study published Wednesday in “Nature” magazine, astronomers from the University of Hawaii’s Institute for Astronomy reported that a planet has potentially survived the expansion of its host star into a red giant.
Stars such as our own sun expand to hundreds of times their size at the ends of their lives, engulfing any planets unfortunate enough to be orbiting too closely — when our sun dies, Earth will be one such casualty.
But using the W. M. Keck Observatory and the Canada-France-Hawaii Telescope, researchers discovered that one distant planet appears to have withstood such an event.
The planet Halla was discovered in 2015 by Korean astronomers, and orbits the star Baekdu. But the IFA team, led by NASA researcher Marc Hon, discovered that Baekdu is burning helium in its core, indicating that it has already undergone the red giant expansion process and has shrunk back to a smaller size.
Based on their observations, Hon’s team determined that the star should have expanded to up to 1.5 times the orbital distance of Halla, which would have engulfed and presumably destroyed the planet. And yet Halla persists in defiance of its star’s infernal heat.
“Planetary engulfment has catastrophic consequences for either the planet or the star itself — or both,” said Hon in a statement. “The fact that Halla has managed to persist in the immediate vicinity of a giant star that would have otherwise engulfed it highlights the planet as an extraordinary survivor.”
But astronomers’ theories for how the planet could have survived such an event suggest that Halla might never have been in danger of being engulfed. One theory posits that Baekdu is actually the remnants of a binary star system that merged into a single star, which may have prevented either star from expanding sufficiently to engulf Halla.
Another theory is that Halla is a “second generation” planet, having been formed from gases left behind by the collision of two stars.
“Most stars are in binary systems, but we don’t yet fully grasp how planets may form around them,” said Hon. “Therefore, it’s plausible that more planets may actually exist around highly evolved stars thanks to binary interactions.”
