Stars like the sun don’t last forever—they eventually expand and envelop the inner members of their planetary systems. But the sun isn’t the only thing going out with a bang—the planets might too. A new study suggests that as a star begins to die and slowly expands outward, it would temporarily light up as it eats the worlds it hosts. If this turns out to be the case, we could potentially catch a star in the act of planetary cannibalism.
“All these planets that were mostly safe for most of the star’s lifetime are now in jeopardy,” says at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, who led the study.
Someday, the sun will expand and devour its children. Mercury and Venus will be toast, and the Earth may be a goner too, enveloped in the dying star.
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A planet like Earth wouldn’t create much of an observable fuss for its star. But in other solar systems, the larger, gas giants that orbit near their star could cause a more pronounced change in brightness. However, it would be short-lived, says at Princeton University, who collaborated on the study.
Speeding towards death
One other potential method of finding a cannibalistic star is to look for disturbances in a star’s rotation. As it feasts on the planet, the star could begin to spin faster. “This ‘spin up’ effect is observable and lasts longer than the luminosity ingestion signature,” Soares-Furtado says.
There are a few hurdles toward confirming their model – MacLeod doesn’t have a full set of criteria for how to confirm that a change in brightness is an act of an aging star eating its children as opposed to the natural variability in some stars. But there are some known acts of stellar cannibalism that could serve as a guideline, including RZ Piscium, an infant star devouring a protoplanet.
Kristina Punzi at the Rochester Institute of Technology in New York, has studied RZ Piscium. She says, “I believe the planets would add their potential energy to the total luminosity of the star as they’re being consumed,” as opposed to being ripped to shreds and left in clouds of chunk matter like the younger system, where clouds of dust burn bright in infrared.
“Our RZ Piscium observations and the models described in this paper are very different, but maybe complementary, methods to investigate the planetary cannibalism phenomenon.”
So, there’s some work to do before we know precisely how this will work, but we may soon know what the other side of the death of the sun will look like. If we identify systems about to evolve to a giant stage, we might be able to witness the system’s destruction, further helping identify candidate cannibals. A better understanding of the mechanics of a star eating its children could also help rule out jumping to the immediate conclusion that aliens are afoot in the phenomenon.
The Astrophysical Journal Letters
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