A star 320 light-years from Earth appears to be eating some of its planets, which may explain why it’s quite different from its sibling star.
Led by Semyeong Oh from Princeton University, the study announcing the finding is available on arXiv. The team used data from ESA’s Gaia telescope, which is busy looking at 1 billion stars in our galaxy, to investigate this phenomenon.
The researchers looked at a binary pair of stars, called HD 240430 and HD 240429, separated by 2 light-years. While they were both born about 4 billion years ago, probably from the same interstellar cloud, they appear to have strangely different chemical compositions.
The reason, according to Oh and her team, may be that the former star has eaten some of its planets, or some of the planetary material that gives rise to them. This has given it a different composition from its companion star, for example it has a higher amount of lithium. The researchers have thus nicknamed the star “Kronos”, after the Greek god who ate his own children.
“We therefore suggest that the star HD 240430, ‘Kronos’, accreted 15 [Earth masses] of rocky material after birth,” the team wrote. Kronos and its companion, dubbed Krios after the lesser-known brother of Kronos, are both Sun-like stars.
Three other theories for their different compositions are proposed, including the difference in age (Kronos is slightly older by about 300 million years), the possibility they were not born from the same cloud, and non-uniformity in the initial cloud itself.
However, the researchers favor the planet idea. Quite why this would have happened around one star but not the other isn’t clear, though. It’s possible a passing star could have disrupted the orbits of Kronos’ inner planets, while Krios was unaffected.
“If this did happen to Kronos, any remaining outer giant planets around it might have stretched-out orbits, suggesting they participated in the same cataclysm that led to the demise of their siblings,” New Scientist noted. “To test this, the team has begun looking for giant planets around both Kronos and Krios.”
This result would be unusual, but not unheard of. We’ve actually found quite a few stars eating planets before, including one spotted by NASA's Hubble telescope in 2010. Here, an extremely hot planet called WASP-12b, in a tight orbit, was seen being ripped apart. A similar world was found in 2016.
What’s more, planet eating has also been considered a possible cause of the “alien megastructure” star, which has been seen dramatically dipping in light on repeated occasions. The debris being released from such a cosmic meal could be blocking the star's light.