A new clue has just been found that could help solve the mystery of a strangely dimming star. KIC 8462852, also known as Boyajian’s Star, appears to have a binary companion that could contribute to its erratic drops in brightness.
If confirmed with more detailed observations, the newly discovered companion star could help astronomers finally solve the ongoing mystery of KIC 8462852.
The star was discovered in 2015 by astronomer Tabetha Boyajian (which is why it was previously Tabby’s Star), and it has since turned out to be a real puzzle. It is a yellow-white dwarf star about 1,470 light-years away and remains irregularly dim. There is no regularity in the timing of the star’s dimming, or depth – some of the dips in the starlight were as deep as 22 percent.
This behavior excludes planets; When an exoplanet passes between a star and Earth while orbiting the Earth, it will dim the star slightly – 1 percent or less – at regular intervals.
Additionally, when Boyajian’s Star dims, some wavelengths are blocked more than others. That rules out a solid object (such as an alien megastructure, as proposed in 2016), which would block all wavelengths equally.
So far, the most likely explanation seems to be optically thin dust and debris, possibly from broken planetesimals or comets in eccentric orbits, in combination with normal brightness variations of the star itself.
The presence of a binary companion star in wide orbit could help explain the presence of all this material, and could create additional gravitational perturbations to disrupt bodies in orbit.
Since 2016, a team of astronomers led by Logan Pearce of the University of Arizona has been trying to confirm the possible connection of a nearby star to KIC 8462852. Their paper has now been accepted in The Astrophysical Journal.
The difficulty of measuring space in three dimensions is what made this work rather difficult. Stars that appear quite close together may be at vastly different distances from the viewer. So Pearce and his team used five years of observations to get accurate astrometric measurements of the faint star that appeared close to KIC 8462852.
“In this work, we use three eras of Keck / NIRC2 astrometry spanning five years to rethink the closest partner status of KIC 8462852, and to demonstrate that they are a common pair of motion and a gravity-bound binary system” , they wrote in their paper.
In addition to the observations from the Keck Observatory, the 2020 release of astrometric data from the Gaia satellite – the most complete and accurate three-dimensional map of the Milky Way to date – also included the faint star, with measurements consistent with the findings of the team.
The two stars are at a distance of 880 astronomical units. Boyajian’s Star, or KIC 8462852 A, is the larger star, about 1.36 times the mass and 1.5 times the size of the sun. Its companion, KIC 8462852 B, is a red dwarf star that is about 0.44 times the mass and 0.45 times the size of the Sun.
With such a wide orbit, KIC 8462852 B probably wouldn’t have a direct effect on the brightness of KIC 8462852 A. But it could still play a role in the larger star’s mystery swings, the researchers said.
“The binary companion can influence the long-term evolution of the system,” they wrote in their paper.
Scientists have previously discovered that widely spaced stellar binaries can be pushed by greater gravitational forces to move very close to their mutual center of gravity several times over the course of about 10 billion years.
This, in turn, can result in the disruption of planets and other small bodies in orbit where they are stretched and ripped apart by gravitational interactions, resulting in clouds of debris.
The scenario has yet to be confirmed. At such a distance, the two stars would have an extremely long orbit and the observations were not enough to characterize this orbit. KIC 8462852 B could be a star thrown from the system; or the two stars could be members of a moving group.
The researchers believe that a binary number is the most likely explanation for their measurements of the two stars, but future measurements of the pair will be needed to better understand their relationship. This could help confirm or rule out KIC 8462852 B’s role in the star’s erratic brightness.
But never fear all mystery lovers. There are other strangely obscuring stars, including one that already has its binary companion accounted for, and a tantalizing collection of 21 stars that could be even stranger.
The team’s investigation has been accepted The Astrophysical Journal, and is available on arXiv.