I have had the opportunity to work with a number of students on various topics. Advising serves as a fantastic opportunity to both expand upon topics with which I am already well-acquainted and to pick up something new. I am always keen to work with new students on a variety of subjects. I list several below.
Mark is a rising Senior in Astrophysics at Princeton. His work seeks to understand the long-term fate of planetary systems after the parent star has ended its life. That is, the Sun will exhaust its nuclear fuel in about 8 billion years. It will then expand, engulfing the planets Mercury and Venus, potentially stopping close to Earth. After this invasion of the inner Solar system, it will shed its bloated exterior and shrink to the size of Earth, while weighing 200,000 times as much. This exotic, dense object is called a white dwarf.
Here’s the mystery–about half of detected white dwarfs seem to have rocks raining onto their surfaces. This is perplexing, given that these objects must have also gone through a “red giant” phase and cleared out any close-in pieces of planetary debris (or planets). Thus, the source of these raining rocks is unknown. Mark’s research tests the idea that moons around extrasolar planets might be the culprits. He models the evolution of systems of moons resembling Jupiter’s to ask where those moons end up–in the star or in the planet?
The Sun’s spin axis is roughly aligned with the orbits of the planets. However, a large number of exoplanetart orbits appear to be misaligned with their stars, with many orbiting the opposite direction. How did these “upside-down” planetary systems come to be?
Rob, a graduate student at Princeton, is looking into whether the planet-forming disk might have been tilted with respect to the host star’s spin axis. His work is providing further tests of a hypothesis proposed in 2012 that suggests that stellar companions might have gravitationally torqued planet-forming disks out of alignment with their host stars.
In our Solar System, all the planets orbit in roughly the same plane, like a giant celestial vinyl record. Are alien planetary systems similarly “flat”? In many cases, they are, but perhaps half of the time planets in a given system are not orbiting in the same plane. How did this happen?
Katee is exploring our hypothesis from 2016 that he central star is the culprit. To elaborate, our Sun spins around its axis about once every month. As it turns out, this is rather stately compared to its youth, when it likely made a full rotation every 3 days or so. This fast rotation would cause the young Sun’s equator to bulge out, changing the Sun’s gravity in just such a way as to pull orbiting planets out of a common plane.
Katee’s work has shown that the aforementioned mechanism correctly predicts that the closer planets live to their stars, the wonkier their orbits get. Moreover, she finds that the squashed star can totally disrupt planetary systems in about 10% of cases.
Henry is a Junior in Astrophysics at Princeton. His work examines the orbital history of Saturn’s largest moon Titan in order to understand the anomalous “eccentricity” of the moon’s orbit. (I.e., its orbit deviates from a perfect circle by a few percent).
Noah’s work from 2018 modelled several planetary systems where the resident planets are known to reside in approximately the same plane. What we found, though, was that if the host star was just a little bit tilted away from the plane of the orbits, the systems would not retain their coplanarity. What this means is that the very existence of some multi-planetary systems places strong constraints upon the orientations of their host stars, a measurement that’s otherwise very difficult to obtain.