Tag Archives: star clusters



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!

Satellites and Streams in Santiago 2015


What a week! The ESO workshop ‘Satellites and Streams in Santiago’ is over now, and I am still amazed by how flawless this meeting was. As announced here a while ago, I’ve been organizing this conference with Steffen Mieske (ESO) for the last few months. In the end we were 107 registered participants plus some 10 guests. The line-up was absolutely amazing, ESO Director General Tim de Zeeuw gave an opening address, and we heard keynote presentations from the who-is-who in the fields of satellites (Jorge Peñarrubia, Michelle Collins, Pavel Kroupa, Rodrigo Ibata, Vasily Belokurov, Gurtina Besla), streams (Steven Majewski, Amina Helmi, Aaron Romanowski) and the star-cluster/dwarf-galaxy interface (Oleg Gnedin, Jay Strader, Dougal Mackey, Michael Hilker, Anil Seth).  Continue reading Satellites and Streams in Santiago 2015

MODEST15 in Concepción

One of my favorite conference series is “Modeling and Observing Dense Stellar Systems” (MODEST). This year, MODEST15 took me to Concepción in the beautiful south of Chile. Flying into Santiago over the Andes is already a spectacle.


But once landed in the south, the beauty of the landscape is breathtaking, and a few hours drive brings you to the most amazing places in the Andes, full of outdoor activities and gorgeous views.  Continue reading MODEST15 in Concepción

How Mass Segregation affects the Expansion of Star Clusters

Orange points show the observed radii (r_h) of Milky Way globular clusters plotted against their distance from the Galactic center (R_G). Globular clusters in the outer halo of the Galaxy tend to be significantly more extended than the ones nearby. Lines show different models for the sizes, star clusters can expand to at a given radius within the age of the Universe.

Recently, my Iranian collaborators and I published another paper on mass segregation in outer-halo globular clusters. This time we looked at the effect that primordial mass segregation can have on the size evolution of these clusters (i.e., what happens if heavy stars are preferentially born closer to a star cluster’s center). The problem is the following: if you look at the globular clusters in the outer halo of our Galaxy, you find them to be significantly more extended (i.e., with a radius larger than 5-6 pc) than their counterparts that are closer to the Galactic center (orange points in the Figure above; but see also my previous posts [1] [2]).  Continue reading How Mass Segregation affects the Expansion of Star Clusters