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!

How to weigh the Milky Way

The Northern Hemisphere of the sky as seen by the Sloan Digital Sky Survey. Stellar streams stick out from the vast number of stars in this view, of which most lie within the Milky Way disk. The Palomar 5 stream is the densest of the stellar streams discovered so far and turned out to be a perfect scale and yardstick for our understanding of the Milky Way. (Credit: Ana Bonaca, Marla Geha and Nitya Kallivayalil with data from the Sloan Digital Sky Survey.)

The Milky Way consists of roughly 100 billion stars like our Sun, which form a huge stellar disk with a diameter of 100-200 thousand light years. The Sun is also part of this structure, hence, when we look into the sky, we look right into this gigantic disk of stars. The vast number of stars and the huge extent on the sky make it hard to measure fundamental quantities for the Milky Way – such as its weight.  Continue reading How to weigh the Milky Way

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

Hubble Fellows Symposium 2015

2015 Hubble_Fellows_Symposium_GroupPhoto 2

Right after getting back from Chile I headed straight to Baltimore for this year’s Hubble Fellows Symposium at the Space Telescope Science Institute. Every year most of the 51 Hubble fellows (three years with each 17 fellows) get together at these meetings to present their work to each other. It is quite a fun meeting, since you get exciting updates on nearly all major fields of astronomy within three days. Last year we criticized, though, that the schedule left no time for chatting, schmoozing and collaborating. This year the organizers relaxed the schedule  a bit, so every talk was only 20 minutes long. It made the meeting much more enjoyable and put the fun back into the symposium.

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

Stream fanning

streamfanning In my first year at Columbia I worked with grad student Sarah Pearson on an idea that Kathryn Johnston had while trying to find an orbit for Palomar 5 in a Law & Majewski potential. Wait what? Who’s Sarah, who’s Palomar 5, and what is a Law & Majewski potential?

Palomar 5 is a globular cluster in the halo of our Galaxy, the Milky Way. It is about 12 billion years old and consists of roughly 30,000 stars. The star cluster can be seen within the footprint of the Sloan Digital Sky Survey. But even more fascinating is that we can also see a stream, consisting of at least as many stars, stretching out from the cluster along its orbit. This stream – there are actually two, one in the leading direction and one in the trailing direction – spans about 23 degrees on the sky, while being on average half a degree wide. That’s about the size of 50 full moons!  Continue reading Stream fanning