Astronomers have found strong evidence that TOI-5882, a sun-like star about 1,300 light-years from Earth, may have devoured one of its own planets.
A research team led by University of Michigan astronomer Brooke Cotten has discovered important clues to the star’s chemical composition. TOI-5882 contains far more lithium than researchers typically expect to find in stars of this type.
“You’re what you eat, right?” said Cotten, a graduate student researcher in UM’s astronomy department and lead author of the new report. astrophysical journal. “We know that planetary material contains much more lithium than stars. So when a star eats a planet, it ingests a lot of lithium.”
This research was supported in part by federal funding from NASA and the National Science Foundation.
How stars swallow planets
Astronomers use the term engulfment to describe what happens when a star swallows a planet. These events unfold very rapidly on the cosmic time scale, sometimes lasting only days or weeks.
This process is so short that scientists are unlikely to catch a star in the process. Instead, we must look for chemical traces and other evidence that will remain after Earth disappears.
“That’s the fun of this field: you’re really solving mysteries,” said Cotten, who began her research as an undergraduate as part of the Ramat program at the University of California, Santa Cruz. “You can’t just watch a crime happen, so you have to use all the clues you’re given to uncover the culprit.”
Learning how to identify these phenomena could help astronomers determine how often stars consume planets and under what circumstances this happens.
Our solar system is expected to experience a similar fate in the distant future. In about 5 billion years, the Sun will reach the later stages of its life and expand into a red giant. As it grows, it will swallow Mercury, Venus, and perhaps Earth.
Brown dwarfs may play a role
TOI-5882 has not yet expanded enough to explain how it swallowed a planet based on its size alone. So the researchers decided to consider another possibility.
Star may have had some help.
A large gaseous object also orbits TOI-5882. Although it has more than 20 times the mass of Jupiter, it is still too small to ignite and become a true star. Astronomers classify this type of object as a brown dwarf.
The brown dwarf may have disrupted the missing planet’s orbit, causing it to crash into TOI-5882. Cotten said the possibility will be investigated in a separate study.
Lithium provides a chemical fingerprint
Lithium provides astronomers with a valuable way to investigate planetary engulfment. Seth Jacobson, lead author of the study and an assistant professor at Michigan State University, said that while stars naturally contain some lithium, planets typically contain much higher concentrations of the element.
“Lithium atoms delivered to a star by a planetary swallow are similar to sports fans arriving at a stadium,” he said. “There may already be some early-arriving fans representing the initial amount of lithium in the star’s atmosphere, but they will soon outnumber them.”
Judging by the amount of lithium detected in TOI-5882, researchers estimate that the engulfed planet may have been somewhere between the mass of Earth and that of Neptune.
“The fact that we can look at a star 1,300 light-years away and confidently say, ‘This star has more lithium than we expected’ is a testament to both the precision of modern instruments and the difficult interpretive work that goes into understanding that signal,” said Melinda Soares Furtado, the study’s senior author and assistant professor at the University of Wisconsin.
Compare TOI-5882 with similar stars
The project brought together 14 researchers from the United States and Chile. The research team searched for signs of lithium in TOI-5882 using spectroscopy, a method that reveals a star’s chemical composition by analyzing its light.
Observations revealed that this star contains a large amount of elements. The next challenge was to prove that its lithium levels were indeed abnormal, rather than normal for a star with similar properties.
To test it, the researchers assembled a comparison group of 62 stars with similar ages, masses, and temperatures. They then evaluated TOI-5882 against those stars using several different methods.
“And it’s not like you have to cherry-pick the data to make it stand out. The data is robust,” Soares Furtado said. “No matter how you slice it, we find that TOI-5882 is very rich in lithium, at least in the 97th percentile.”
A rare star that left behind evidence
The study builds on previous work by Soares Furtado, which identified the types of stars most likely to preserve evidence of planetary engulfment.
Many stars are poor candidates because chemical signatures from engulfed planets can disappear or become difficult to distinguish. However, TOI-5882 appeared to be one of the rare stars for which evidence could still be detected.
Several stars in the comparison group also showed unexpectedly high lithium levels. The discovery suggests that planetary swallowing may not be the only process by which stars can concentrate lithium, raising new questions for astronomers to investigate.
For Cotten, uncertainty is part of the appeal.
“When I was a kid, I dreamed of being a private investigator,” she said. “I think that explains a lot about where I ended up. I feel like a detective.”
