University of Virginia


Last week I visited Jennifer Sobeck and my former Yale-colleague Nitya Kallivayalil at the University of Virginia. Jen is the deputy project manager of APOGEE-2, which is a large spectroscopic survey collecting 300,000 high-resolution spectra of Milky Way stars (and other bright targets). Hence, her head is full of stellar atmospheres and element abundances. Nitya is the go-to person for proper motions of Galactic satellites, which is why there’s tons of overlap between my work and both of theirs. Frequently distracted by great food and stunning weather, we scienced around for a few days. Our brainstorming for low hanging fruits in the APOGEE-2 dataset brought us a few great ideas, which we will hopefully pursue within the next weeks and months. Steve Majewski, PI of APOGEE and also based at UVa, outsourced the same task to all his undergrads. Let’s see who’s first to have some results!

Hubble Fellows Symposium 2016


It was great to visit Baltimore one last time and see the other fellows again. Baltimore has become a major hub for astronomy, even more so since STScI started hiring for JWST and WFIRST. All my friends from Yale seem to live in Baltimore now!

Big in Japan

I get to be on Japanese television!! NHK, Japan’s national public broadcasting organization, asked me for an interview about the evolution of globular clusters and the formation of tidal streams. I’m still excited about it, it was so much fun!


NHK produces a show called Cosmic Front Next, which covers one aspect of astronomy per episode. Each episode is one hour long and features several scientists. Since 2011, they have aired about one episode per week. That’s a lot of astronomy! Surprisingly, they haven’t covered globular clusters yet. So, I’m more than happy that I get to be on this episode of Season 5. Continue reading Big in Japan

Chaos in the Galaxy

N-body simulations of tidal streams formed by Galactic satellites on regular orbits (A & B), a weakly chaotic orbit (C), and a strongly chaotic (D). The orbits of the four satellites are quite similar in terms of eccentricity and apo/pericenters, but the resulting streams show (and amplify) the underlying chaos.

During Adrian Price-Whelan’s dissertation talk today at the winter meeting (AAS227) of the American Astronomical Society in Kissimmee, Florida,  I was reminded that I haven’t mentioned our publication here. Adrian went through a whole lot of effort and characterized regular and chaotic orbits in a typical galactic gravitational potential. Usually, orbits in such a potential can be broadly categorized into chaotic and non-chaotic orbits. Adrian looked at this distinction in terms of the streams that are formed by satellites on such orbits. Continue reading Chaos in the Galaxy

ESO Messenger


An article I just wrote with Steffen Mieske (ESO) about our Satellites and Streams in Santiago meeting earlier this year appeared today in the ESO Messenger. Go, check it out!

Stream Meeting Ringberg Castle

It’s been a while since I’ve found the time to give an update on my activities. The reason is that there are just too many these days! Let me start catching up by telling you about an amazing workshop that took place from July 19-24 in Germany.


Jo Bovy (CITA) and Hans-Walter Rix (MPIA) organized a stream meeting at Ringberg Castle, which is a conference venue owned by the Max Planck Society. It’s not just called ‘castle’, it really is one! And the conference participants are literally locked up on a mountain, giving the meetings up there a very intimate and focussed atmosphere. I was put in the tower – but with a view like that (above) it didn’t occur to me to complain!  Continue reading Stream Meeting Ringberg Castle



On the last Monday of April we had our first meeting of star cluster aficionados in New York: GONYC – Globular, Open, Nuclear and Young massive star Clusters. Together with Nathan Leigh from the American Museum of Natural History I initiated this monthly get-together, because we both felt a bit detached from the rest of the star cluster community. This is mostly due to the fact that star cluster research is significantly underrepresented in the U.S., so we have to connect more actively across institutions. We decided to meet at the AMNH since it is the birthplace of one of the most important conference series in the star cluster community – the MODEST meetings. The long-term goal is to host a MODEST meeting at the AMNH again after the first one in 2002. It’s a great time for GONYC – the rapidly growing fields of nuclear star clusters, young massive star clusters, and super-massive star clusters like UCDs has boosted interest in basic gravitational dynamics and star cluster physics. If you want to join the meetings (next one is on May 20) contact me or Nathan!