A Sun-like star swallowed a planet. Lithium does not deceive

Lithium tends to have a low concentration in stars and higher concentration in planets. The discovery of a twin star to the Sun with a large concentration of lithium indicates that the star swallowed a planet.

A team of astronomers, led by Brooke Kotten of the University of Michigan, has demonstrated that TOI-5882 – a Sun-like star located about 1,300 light-years away – is likely swallowed one of your planets.

While a star may seem like the perfect incinerator for destroying evidence, the team still found revealing clues in TOI-5882’s chemical makeup, specifically its unusually high concentration of lithium.

“We are what we eat, right?”said Kotten, a researcher in the Department of Astronomy at the University of Michigan and lead author of the new scientific article in The Astrophysical Journal. “We know that there is much more lithium in planetary material than in stars. So if a star swallows a planet, it will absorb a lot of lithium.”

When a star consumes a planet, astronomers call it “engulfment.” In astronomical terms, the process is incredibly fasttaking weeks or even days. This means that astronomers cannot count on observing an engulfment event as it occurs, Kotten explained, which is why it is important to develop methods that help researchers study such events after they have occurred.

“That’s what makes this area so exciting. We are truly solving a mystery“, said Kotten, who began working on this study while a college student at the University of California, Santa Cruz. “We can’t just watch the crime, so we have to work with every clue we are given to find out who did it.”

By working to solve these cases, astronomers can better understand how common planetary engulfment is and the different ways it can occur. For example, about 5 billion years from nowour Sun will enter the final stages of its life and will transform into what is called a red giant. As it swells, it will swallow Mercury, Venus and perhaps Earth.

But TOI-5882 has not yet swelled to the point where its expansion is a likely explanation for why it swallowed a planet. However, the team came forward with an intriguing alternative: the star may have had an accomplice.

Also orbiting TOI-5882 is a giant ball of gas more than 20 times the mass of Jupiter, but not yet large enough to grow into a star. This object, called a brown dwarf, may have helped direct the swallowed planet to TOI-5882but testing that theory will be the subject of a separate study, Kotten said.

Investigating the case

Lithium is powerful forensic evidence because although stars naturally possess it in small amounts, planets have a much higher concentration of this elementsaid Seth Jacobson, one of the study’s lead authors and an assistant professor at Michigan State University.

“Lithium atoms delivered by planetary engulfment to a star They are like fans arriving at a stadium“, he said. “There may already be some early adopters, representing the initial amount of lithium in the stellar atmosphere, but they are quickly outnumbered.”

Based on the amount of lithium that researchers observed, they suspect that the planet that TOI-5882 swallowed had a mass somewhere between twice that of Earth and that of Neptune.

“The fact that we can look at a star 1,300 light years away and say with confidence, ‘This star has more lithium than you would expect,’ is a testament to both the precision of modern instrumentation as well as the hard work of interpretation necessary to make sense of this signal”, said Melinda Soares-Furtado, senior author of the study and assistant professor at the University of Wisconsin.

Fourteen experts from the US and Chile came together for this project. A technique known as spectroscopy allowed the team to analyze the light coming from TOI-5882 for signs of lithium. From the star’s spectra, researchers were able to determine that it had a high lithium content, but then had to prove that this level was abnormally high.

Therefore, they gathered a set of 62 control stars comparable across several criteria, including age, mass and temperature. The team then compared, in several ways, TOI-5882 to this control group.

“And it’s not like you need to choose the data in a biased way to make it stand out. It’s a robust result“, said Soares-Furtado. “Regardless of how you analyze it, TOI-5882 is so rich in lithium that it is at least in the 97th percentile”.

The study was also based on previous work by Soares-Furtado which indicated that TOI-5882 could, in fact, be analyzed to detect signs of engulfment. She had explored the characteristics that a star would need to possess to show signs of engulfment events, and unfortunately, many stars do not fit these criteria, he said. But TOI-5882 was one of the rare exceptions.

Interestingly, some of the other stars in the control sample also showed high concentrations of lithium, suggesting there may be other enrichment mechanisms at work that researchers could explore. As is often the case in science, answering a question can create mysteries, which is exciting news for astronomers like Kotten.

“When I was a child, I dreamed of becoming a private detective,” she said. “I think that explains very well where I ended up. I really feel like a detective“.