Eccentric Dynamics

My group studies all things eccentric (hover over image for names). We are particularly interested in relativistic stellar and gas dynamics near massive black holes, with applications to our Galactic center, the Andromeda (M31) nucleus, and post-starburst galaxies. We're also working on the strange orbits of icy bodies in the outer solar system, the dynamics of dark matter in disk galaxies, gravitational wave recoil kicks of black holes, and white dwarf pollution.

              (Spring 2024) Graduate student Constanza Echiburú-Trujillo joins our group.
              (Aug 2023) I am the Undergraduate Associate Chair of the APS department!
              (Spring 2023) Graduate student Jane Bright (University of Arizona) joins our group.
              (Aug 2020) Graduate student Tatsuya Akiba joins our group.
              (Aug 2019) New postdocs Angela Collier & Maria Tiongco join our group.
              (Aug 2018) I am a Packard Fellow!
              (Sept 2018) I gave a TEDx Boulder talk.
              (Aug 2018) Aleksey Generozov joins our group as a JILA Postdoctoral Research Associate.

In 2016, I joined the Department of Astrophysical and Planetary Sciences (APS) at CU Boulder as an Assistant Professor of Astrophysics and a JILA Fellow. Before this, I was a NASA Einstein & Theoretical Astrophysics Center Postdoctoral Fellow at UC Berkeley. I received my Masters and PhD (2012) in Astronomy at Leiden Observatory in the Netherlands, and my undergraduate degree in Physics & Astronomy at the National University of Ireland, Galway.

A Note for Prospective Graduate Students

If you are interested in working in my research group, please apply to the APS (distinct from Physics) department at CU Boulder. No need to email me; admissions are managed by a separate internal committee. If you are admitted you will be invited for a department visit in the spring when we can discuss more science. I don’t yet know if I will have openings starting next Fall but I'm interested in bringing in 1-3 new students into my group over the next few years.
Need more information? Click here! Best of luck with your applications!

Research Highlights

Instability in the outer solar system

The orbits of icy minor planets beyond Neptune are doing something very strange: they all tilt and pitch in similar ways, and maybe even cluster together on the sky. In a 2016 paper, my collaborator Mike McCourt and I show that when gravitational forces between minor planets on eccentric orbits are included in N-body simulations, the orbits incline rapidly off the disk plane, and tilt and pitch in exactly the same way. This gravitational instability is something that a disk of eccentric orbits does on its own -- we don't need to invoke an external reason (like a planet 9) for it. We do, however, predict a lot of minor planets in the outer Solar System, a "new Kuiper Belt" (with an order of magnitude more mass!), to defend the orbital clustering against the precessing effects of the giant planets.

We now have a whole series of papers on this topic, including an explanation of the dynamics behind the collective gravity mechanism and the discovery of eccentricity oscillations when we include a spectrum of minor planet masses.

We recently (April 2020) submitted a paper on the effects of the giant planets on a primordial scattered disk and a letter showing that the collective gravity of extreme Trans-Neptunian Objects can result in apsidal clustering.

Gas clouds plunging through an accretion disk

The physics of how gas accretes onto supermassive black holes is hugely important in astrophysics. It is a difficult topic of research however, involving three-dimensional, hot, magnetic plasmas. In a 2017 study, we used the G1 and G2 gas clouds in the Galactic center as probes of the accretion flow around SgrA*. As they plunge through the background gas, their orbits change due to dynamical friction. By analyzing these changes, we showed that the rotation axis of the accretion flow points along that of the Galaxy and of a putative jet! We also found that the pericenter passage date of G2 was delayed, due to precession of its eccentricity vector. It likely occured in August 2014, several months after the G2 observing campaign ended. Interestingly, this coincided with an increase in both the rate and luminosity of X-ray flares from SgrA*.

Eccentric stellar disks orbiting massive black holes

The double nucleus of the Andromeda galaxy has been a puzzle since its discovery by balloon-borne experiments in the early 1970s. It is best modeled as a single eccentric disk of stars, which orbits a massive black hole. But how is such an old (Gyr) disk stable? The orbits should differentially precess with respect to one another on Myr timescales! In collaboration with Andrew Halle and Mackenzie Moody, I've discovered that the stability mechanism works like a pendulum - perturbed orbits oscillate about the mean body of the disk due to gravitational torques which changes their eccentriticies and hence their precession rates. Many orbits reached very high eccentricities and the stars are vulnerable to being tidally disrupted by the massive black hole. Check out our original 2018 paper, plus our explorations on the effects of general relativity and mass segregation!


Spring 2024

Black Holes
Undergraduate course (ASTR 2030)
Students can access all course materials on Canvas.
Interested in the CU Honors Program?
Students please read the info here (forms located here), and get in contact with the current APS Honors representative you have any questions.

Current and Former Group Members & Collaborators


Graduate Students

Undergraduate Students

  • Lucy Walton (CU Boulder)
  • Selah Mcintyre (CU Boulder)
  • Alexandra (Sasha) Gladkova (CU Boulder)
  • Karin Roley (CU Boulder)
  • Allie Christensen (CU Boulder)
  • Emma Lieb (CU Boulder)
  • Alexander Rodriguez (CU Boulder)
  • Andrew Halle (UC Berkeley)
  • Jacob Fleisig (CU Boulder)
  • Hayden Foote (CU Boulder)
  • Gwendalynn Roebke (CU Boulder)