The study of planets beyond the solar system has led to some astounding discoveries, many of which have defied astronomers’ expectations and challenged our notions of the forms planetary systems can take. For example, the discovery of Jupiter-sized planets orbiting close to their stars (“Hot Jupiters”) defied what astronomers suspected about gas giants. Previously, the general consensus was that gas giants form outside the “Frost Line” – the boundary above which volatile elements (such as water) freeze solid – and remain there for the rest of their lives.
Interestingly, this will happen when our sun exits the main sequence phase and enters the red giant branch (RGB) phase. This raises the question of what happens to hot Jupiters when their parent stars expand into Red Giants. Using advanced 3D simulations, a team of researchers led by the Compact object mergers: population astrophysics and statistics (COMPAS) consortium simulated how red giants will expand to engulf Hot Jupiters. Their findings could answer another mystery facing astronomers, which is why some binary systems have one rapidly rotating star with strange chemical compositions.
The research was led by Mike Lau, a Ph.D. student at Monash University’s School of Physics and Astronomy, and other members of the COMPAS consortium, a collaborative effort to study the evolution of binary systems. They were joined by members of The ARC Center of Excellence for Gravitational Wave Discovery (OzGrav), the Center for Computational Astrophysics at the Flatiron Institute, Princeton University, and the Harvard & Smithsonian Center for Astrophysics (CfA). Their newspaper, “Hot Jupiter engulfment by a red giant in 3D hydrodynamics”, recently appeared in the Monthly Notices from the Royal Astronomical Society.
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As Lau explained to Universe Today via email, the topic of hot Jupiter engulfment is of interest to astrophysicists because they believe it may explain some of the “strange” stars observed in our galaxy — rapidly rotating and chemically enriched giant stars. . The recent explosion of exoplanet discoveries has allowed several theories to be tested, including the possibility that when stars expand to become red giants, planets that used to orbit at a safe distance will spin toward the star’s center, causing stellarity. material is stored. . Said Lau:
“This is therefore one way to explain observed fast-rotating giant stars”. Also, any planetary material released during the in-spiral could alter the chemical composition of the star’s surface. This may help us understand why a small fraction of the stars are abnormally rich in lithium. Finally, we may be able to directly detect this process by looking for stars that have swelled and brightened by eating a planet, although we would have to be very lucky to catch them in the act.“
The ability to directly observe engulfments and the resulting effect on stars will be possible thanks to next-generation space telescopes such as the James Webb and ground-based telescopes with 30-metre (~98 ft) primary mirrors. This includes the Extremely large telescope (ELT), the Giant Magellan Telescope (GMT) — both of which are under construction in Chile’s Atacama Desert — and the Thirty meters telescope (TMT), currently built at Mauna Kea, Hawaii. Using a combination of adaptive optics, coronagraphs and spectrometers, these observatories instantly detect exoplanets orbiting close to their stars.
In the meantime, Lau and his colleagues ran a series of 3D hydrodynamic simulations that mimicked the engulfment process. As he described it:
“We used a method called flattened particle hydrodynamics. This represents the giant star and hot Jupiter as collections of particles that follow the movement of the liquid, like a ball pit but with millions of balls. This technique has also been used to visualize liquids in video games and animations. An important result of our simulation is that the hot Jupiter may lose most of its material due to friction as it spirals into the star.”
In the future, Lau and his colleagues hope that further advances in computer science will enable higher-resolution simulations. If confirmed, their results could explain rapidly rotating stars with abnormal chemical compositions in binary systems. They also provide a preview of what future studies will show when they examine these systems and their exoplanets and can obtain spectra from them directly.
Read further: arXiv