Michael Petersen

I am an astronomer at the Royal Observatory Edinburgh, University of Edinburgh.

My research focuses on galactic dynamics, using stellar motions and structure to probe the nature of dark matter—particularly in the Milky Way. I combine theory, simulations, and observations, with an emphasis on developing high-precision numerical techniques.

Previously, I was at the Institut d’Astrophysique de Paris and studied at the University of Massachusetts Amherst.

Contact: michael.petersen@roe.ac.uk

Research Focus

I study how gravitational interactions shape galaxies, with a particular focus on the Milky Way. My work treats the Galaxy both as an isolated dynamical system and as one undergoing ongoing interactions, notably with its most massive satellite.

If you are a student at the University of Edinburgh and are interested in a project, please get in touch. I maintain a list of project ideas at a range of levels.

The Large Magellanic Cloud as a Dynamical Probe

The Large Magellanic Cloud provides a uniquely powerful laboratory for dynamical modelling, spanning analytic theory, numerical simulations, and observational interpretation.

With Jorge Peñarrubia, I predicted a dipole signature in the Milky Way’s stellar halo arising from the reflex motion of the disc induced by the LMC. We subsequently detected this signal in distant halo tracers, providing direct evidence of the LMC’s ongoing dynamical influence. Further details and press coverage are available here.

I am also interested in the origin of the LMC and what it reveals about galaxy assembly. In a recent paper, I used simulations to guide a search for stellar tracers in the LMC’s leading arm, identifying candidate stars at large Galactocentric distances.

Model of the LMC moving through the Milky Way halo, shown in density and tangential velocity for concentrated and extended tracers.

Methods: Basis Functions and Time-Series Analysis

Much of my work relies on basis function expansions (BFE) to model collisionless systems. This has motivated methodological advances, described in this paper. A summary of related projects can be found here.

I have also developed applications of Multichannel Singular Spectrum Analysis (MSSA) to isolate coherent dynamical signals in simulations and data. More details are available on this page.

Barred Galaxies and Dark Matter Response

Bars are the most common non-axisymmetric structures in disc galaxies. My thesis combined simulations and analytic calculations to examine the physical mechanisms governing bar formation and evolution.

This work led to the identification of a resonantly trapped component of the dark matter halo that mirrors the stellar bar—the “shadow bar.” A detailed overview is available here, or see the MNRAS paper.

Stellar bar (top) and shadow bar (bottom).

The coupled stellar and shadow bars induce non-axisymmetric structure in the dark matter halo at the solar radius, with implications for terrestrial direct-detection experiments. See Phys. Rev. D for details.