When Stars eat Their Planets, the Carnage can be Seen Billions of Years Later - by BrianKoberlein
Astronomers use this effect to distinguish between high-mass brown dwarfs and low-mass stars. If there is plenty of lithium present in the atmosphere, then fusion isn’t happening, and it’s a brown dwarf. Not much lithium and you have a star. But some stars have atmospheric lithium. They are clearly large enough and hot enough to undergo fusion, and they haven’t burned lithium out of their atmosphere.
Modeled abundances for a star that consumes a planet vs one that does not. Credit: Savilla, J., et al The common hypothesis has been that these unusual stars must undergo some unusual internal mixing that somehow prevents lithium from being cycled into the star’s interior where it can be consumed. This latest study proposes an alternative. Perhaps these stars happened to consume their young planets instead.
Since planets don’t burn lithium when a planet is eaten by a star its lithium is added into the star’s mix. The team simulated how that added lithium would behave in a star’s interior, and how long it would take to fade from the star’s upper layers. They found that smaller red dwarf stars are fairly effective in burning the new lithium. Because a small star has large convection zones that mix its interior really well, within a few hundred million years the new lithium is depleted.
So if we see an old Sun-like star with lithium in its atmosphere, it’s quite possible it once had planets. Stellar lithium seems to be a good sign of a sated star after a planetary meal.
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