Princeton researchers describe ‘Kronos’ star

University researchers have recently discovered twin stars, one of which has shown signs of ingesting a dozen or more of its own rocky planets, according to a University release. As a nod to ancient mythology, the researchers have named the newly discovered stars after Kronos and his lesser-known brother Krios.

The punchline? In mythology, the Titan Kronos devoured his own children, including Poseidon, Hades, and three of his daughters.

The paper describing the new stars and their discovery was authored by Semyeong Oh, Adrian Price-Whelan, John Brewer, David Hogg, David Spergel ’82, and Justin Myles.

Oh GS, a graduate student in astrophysical sciences who is the first author on a new paper describing Kronos and Krios, could not be reached by the “Prince” for comment by the time of publication.

Price-Whelan is a Lyman Spitzer, Jr. postdoctoral fellow in astrophysical sciences. Brewer is a postdoctoral associate in the Department of Astronomy at Yale University. Hogg is a professor of physics and data science at New York University. Spergel is a University astronomy professor and director of the Flatiron Institute’s Center for Computational Astrophysics. Myles is currently a graduate student at Stanford University.

Price-Whelan, Brewer, Hogg, Spergel, and Myles could not be reached by the “Prince” for comment by the time of publication.

According to the University's statement, the researchers have noted that, though other co-moving star pairs have had different chemistries, none are as dramatic as Kronos and Krios.

Most stars that are as metal-rich as Kronos "have all the other elements enhanced at a similar level,” Oh said. She explained that Kronos instead has volatile elements suppressed, making the star stand out in the general context of stellar abundance patterns.

The press release and paper outline Kronos' unusually high level of rock-forming minerals, including magnesium, aluminum, silicon, iron, chromium, and yttrium, without an equally high level of volatile compounds — those that are most often found in gas form, like oxygen, carbon, nitrogen, and potassium.

In her research, Oh immediately observed that Kronos was low in all of the minerals that solidify below 1200 degrees Kelvin, while all the minerals that solidify at warmer temperatures were abundant.

“Other processes that change the abundance of elements generically throughout the galaxy don’t give you a trend like that,” said Price-Whelan. “They would selectively enhance certain elements, and it would appear random if you plotted it versus condensation temperatures. The fact that there’s a trend there hinted towards something related to planet formation rather than galactic chemical evolution.”

According to the press release, this revelation marked Oh's “Eureka!” moment.

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“All of the elements that would make up a rocky planet are exactly the elements that are enhanced on Kronos, and the volatile elements are not enhanced, so that provides a strong argument for a planet engulfment scenario, instead of something else," she said.

Following this revelation, Oh and her colleagues calculated that it would require engulfing roughly 15 Earth-mass planets to gain this many rock-forming minerals without many volatiles.

Eating a gas giant wouldn’t give the same result, Price-Whelan explained. Jupiter, for example, has an inner rocky core that could easily have 15 Earth masses of rocky material, but “if you were to take Jupiter and throw it into a star, Jupiter also has this huge gaseous envelope, so you’d also enhance carbon, nitrogen — the volatiles that Semyeong mentioned,” he said. “To flip it around, you have to throw in a bunch of smaller planets.”

This research has implication for stellar formation models, noted Price-Whelan.

The Flatiron Institute is the intramural research division of the Simons Foundation. The Simons Foundation could not be reached for comment by the time of publication.