Some Stars Chew Up and Spit Out Their Planets — But It’s Not a Death Sentence

That’s some tough parenting.

by Universe Today and PAUL M. SUTTER
The planet's orbit is close to the star. A hot exoplanet orbits a red supergiant.

xAs tragic as it sounds, the engulfment of a planetary object by its stellar parent is a common scenario throughout the Universe. But it doesn’t have to end in doom. A team of astrophysicists has used computer simulations to discover that planets can not only survive when their star eats them — they can also drive their future evolution.

Models of the formation of planetary systems have shown that many planets often end up being consumed by their parent star. It’s simply a matter of orbital dynamics.

Random interactions among newly forming planets and the protoplanetary disk surrounding a young star can send planets on chaotic trajectories. Some of those trajectories drive the planet out of the system altogether, while other trajectories send them hurtling into the star.

Another chance for engulfment happens near the end of a star’s life when it becomes a red giant. This, too, affects the gravitational dynamics of the system and can send some large planets into the atmosphere of their parent star.

Surviving engulfment

To survive engulfment, a planet itself must be relatively large — at least the mass of Jupiter.

NASA, ESA, A. Simon (Goddard Space Flight Center), and M.H. Wong (University of California, Berkeley)

But surprisingly, the planet doesn’t always die when this happens. Astronomers have found many odd systems throughout the galaxy that indicate that planets have survived their journey into the star. For example, there are white dwarf systems orbited very closely by a giant planet, too close for that planet to have formed naturally. There are stars with a surprising amount of heavier metals in their atmospheres, indicating that a rocky object has plunged into it. And some stars are rotating far too quickly, their spin rate amplified by an infalling planet.

All of these systems might result from planetary engulfment, with the planet affecting the further evolution of the star. But can a planet really survive in the intense atmosphere of a star? A team of astrophysicists set out to tackle that question using computer simulations of the interior of a star, tracking the evolution and fate of various kinds of planets that might fall into it. In their simulations, they studied planets of various masses and also brown dwarfs. Their simulations bolster the idea that planets can survive engulfment.

For example, in some cases, the planet can live for thousands of years, swirling around the center of the star within its atmosphere. This orbital action can fling off material from the star, thinning out the outer edges of the atmosphere. In other cases, the exchange of orbital energy drives up the temperature of the stellar atmosphere, making it appear much brighter than it usually would.

But to survive engulfment, the planet itself must be relatively large, at least the mass of Jupiter. Small planets like the Earth cannot last long in those conditions. But if the planet is big enough and depending on the precise evolution, the planet can survive its passage through the star and, in fact, accelerate the evolution of the star so that it ends its life quickly, freeing the planet from its deadly embrace.

This article was originally published on Universe Today by Paul M. Sutter. Read the original article here.

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