"Tails" of Close Encounters Between Red Giants and Brown Dwarfs

Near the end of their lives, Sun-like stars become luminous red giants – they expand over a hundred times in radius and their outer layers cool. These red giants pulsate, changing in brightness periodically, and they lose mass through thick, dusty winds. Planets and brown dwarfs (objects bigger than planets but smaller than stars) orbiting nearby can be strongly affected by these dramatic changes. This project will use supercomputer simulations to explore what happens to close-in planets and brown dwarfs as their host stars evolve. Can these companions survive in such extreme red giant environments? If so, how do their properties, such as mass, temperature, and composition, change over time? The project will also examine how planets and brown dwarfs, in turn, affect the red giants and their dusty outflows. In carrying out the research, PhD and undergraduate students will be mentored and trained not only in astrophysics, but also in high performance computing, data science, analysis and visualization. The research team will also build connections with the local community, creating opportunities to enhance public understanding of science. This project will advance understanding of how planets and brown dwarfs may influence, and be influenced by, their evolving stellar hosts. A key question to be addressed is whether the presence of planets and brown dwarfs can explain the mysterious "Long-Secondary Periods" (LSPs). LSPs are periodic dimming events that may be caused by low-mass companions with dusty, comet-like tails that block the stars’ light as they orbit. LSPs have been seen in tens of thousands of red giants. If planets and brown dwarfs are indeed responsible for these brightness changes, it would open a new window into a vast population of distant planetary systems in the late stages of evolution —systems that would otherwise be difficult to detect and study. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.