Tag Archives: yale

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!


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

Tidal streams in an evolving dark matter halo


2014 has been a great scientific year for me, in which I had the opportunity to contribute to many exciting projects. I’m very fond of the paper that came out of my collaboration with Ana Bonaca and Marla Geha, which we started back in 2013 when I was at Yale. Ana, who is a PhD student at Yale and who got famous for discovering the Triangulum stream in the southern part of the Sloan Digital Sky Survey, put a lot of effort into this project, and I’ve learned a lot from working with her.  Continue reading Tidal streams in an evolving dark matter halo



Quick stop in Oxford on the way to Liverpool. Gorgeous town with inevitable Harry-Potter feeling. The architects must have been inspired by J.K. Rowling and by the much more authentic colleges of Yale and Harvard.

Johns Hopkins


Last night I arrived in Baltimore, Maryland, which PR agents in the 70’s tried to dub as Charm City. Anyone who has seen The Wire knows that this is nothing but a bold face lie. Nevertheless, I’ve enjoyed a nice and sunny Sunday walking across the campus of Johns Hopkins University, through some sketchy neighborhoods of Baltimore, all the way down to the nicer and more gentrified parts of town. I must admit, Baltimore got its charm. Especially the independent coffee shops far off the touristy parts around the Inner Harbor area appealed to me. The next few days will give me some more time to make up my mind about this city: the 2014 Hubble Fellows Symposium is being hosted by the Space Telescope Science Institute until Wednesday. Almost all of the about 50 current Hubble Fellows are getting together to enjoy each other’s science and company. A first trip to a local bar with my former Yale colleagues Rachel Bezanson and Erik Tollerud started off sciency with a discussion of the premier of the new COSMOS earlier this evening, but ended up in watching the finale of True Detective on HBO, and talking over drinks with random townsfolk. Quite a day.



Steffen and I just got back from our trip to New Haven, where we’ve been for the last three days. Going to Yale is always a bit like coming home. So many people to meet and greet, so much to catch up on. One reason why it feels so much like home is because you randomly meet people in the street. That clearly doesn’t happen in New York very often.  Continue reading YCAA



After a busy but very successful week, Alejandro and Mathieu took me out for a pre-weekend drink. We ended up in a place in their neighborhood in Harlem called “Bier International”, and it turned out to be a fountain of joy and delight. I had great German beer – Reissdorf and Jever – which came with a classy selection of hearty Wurst and tasty Brezel. No doubt this place is going to be my second home in summer when you can sit outside on Frederick Douglass Boulevard. By the number of coffee shops, bars and restaurants opening up in this area you may think “this is going to be the new SoHo” (wishful thinking of Mathieu).  Continue reading Bier