What Happens to Hot Jupiters when their Star Becomes a Red Giant?

The study of extrasolar planets has led to some amazing discoveries, many of which have surprised the experts. The discovery of Jupiter-sized planets that were close to their stars was contrary to what they had thought. The general consensus was that gas giants form beyond theFrost Line and stay there for the rest of their life.

When our Sun leaves its main sequence phase, it will enter the red giant branch phase. What happens to hot Jupiters when their parents become Red Giants? A group of researchers led by the Compact Object Mergers: Population Astrophysics and Statistics (COMPAS) consortium simulations how red giants will expand to hot Jupiters. Some systems have one rapidly-rotating star with strange chemical compositions that could be answered by their findings.

The research was led by Mike Lau, a PhD student at the school of physics and astronomy at the university. They were joined by members of several other organizations. Their paper was published in the Monthly Notices of the Royal Astronomical Society.

According to Lau, the topic of Jupiter Hot engulfment is of interest to astrophysicists because they believe it may explain some of the "odd" stars that have been observed in our universe. The recent explosion in exoplanet discoveries has allowed for various theories to be tested, including the possibility that when stars expand to become Red Giants, planets that used to be at a safe distance will spiral toward the star. Lau said, "Yes."

One way of explaining fast rotating giant stars is this. Any planetary material that comes off during the in-spiral could change the makeup of the stars. We may be able to understand why a small fraction of stars have high levels of the substance. We might be able to detect this process by looking for stars that have swollen up and brightened from eating a planet, though we will have to be very lucky to catch them in the act.

The ability to directly observe stars will be possible thanks to next- generation space telescopes. The ELT, the Giant Magellan Telescope, and the Thirty Meter Telescope are currently being built in Hawaii, and are part of this. The telescopes will be able to detect exoplanets that are close to their stars.

Lau and his colleagues recreated the engulfment process in a series of simulations. He described it that way.

“We used a method called smoothed particle hydrodynamics. This represents the giant star and hot Jupiter as collections of particles that follows the fluid’s motion, like a ball pit but with millions of balls. This technique has also been used to visualise fluids in video games and animations. A key result from our simulation is that the hot Jupiter may lose most of its material due to friction as it spirals into the star.”

Lau and his colleagues hope that higher-resolution simulations will be possible in the future. Their results could be used to account for stars with strange chemical makeups. They give a preview of what future surveys will show when they look at these systems and their exoplanets.

ArXiv is further reading.