ISIMA 2014 Toronto

Lonely moose guarding the gate of the University of Toronto

I spent all of August in beautiful Canada at the University of Toronto for the International Summer Institute for Modeling in Astrophysics (ISIMA).

Trinity College

ISIMA is organized by the Theoretical Astronomy and Astrophysics department of UC Santa Cruz. It takes place on a regular basis every few years, and was this time hosted by the Canadian Institute for Theoretical Astrophysics (CITA) at the University of Toronto.

View from the Canadian Institute for Theoretical Astrophysics (CITA)

The University of Toronto was Canada’s first university and was founded in 1827. I literally didn’t expect anything of this place, so I was more than pleased to find a beautiful university in the heart of this fascinating city! Both university and city made this year’s edition of ISIMA a fun adventure.

View from CITA on downtown Toronto

Each ISIMA has a different modeling theme, and this year’s topic was gravitational dynamics. Chair of the summer institute was Pascale Garaud, professor in applied mathematics at UCSC.

Interesting architecture of the University of Toronto

The first week of the six-week program she laid out more like a conference. In the morning we heard lectures, and in the afternoon we had talk sessions.

Interesting architecture of the Royal Ontario Museum

Pascale organized four renown senior lecturers, Scott Tremaine, Douglas Heggie, Doug Lin, and David Merritt, who all gave great introductions to several aspects of gravitational dynamics.

Random downtown building

Less senior people like me, and many other of my gravity friends (yes, we’re gravity friends), were given the opportunity to present their current research and advertise our student projects, which we had to design before coming to Toronto.

Downtown Toronto

The main purpose of ISIMA is bringing  students and advanced researchers from all over the world together to do research together on new and interesting projects. 15 grad students attended the summer institute, and within the first week they had to chose a project with one of the postdocs, junior or senior faculty. For the rest of the six-week program, they then worked on these projects and in the last week presented their results. Many of the projects were designed such that they could be finished within the 5 weeks. Some may need some more work back home, but all of them may end up in actual publications! A win-win for all participants.

The waterfront

Fortunately, it was not just all about work. It was summer at last, and Toronto turned out to be absolutely amazing. I shared an apartment with Shangfei Liu, Mark Gieles and Florent Renaud. Our neighbors within the student dorm were Pascale, Sukanya Chakrabarti, Allice Quillen, Elena d’Onghia and Anna-Lisa Varri.

Kensington Market: alternative/hipster/hippie part of town right next to the University

We went out together, had potluck dinners in the dorm, or joined the students on a few of their numerous excursions to the fun parts of town.

Colorful Kensington Market

Most of these excursions went to Kensington Market, a colorful neighborhood right next to the University of Toronto.

Everything is artsy in Kensington
And political/critical
Chinatown is right next door

One group excursion took us to Niagara Falls, which is about 1 hour drive from Toronto – or 4 hours if you stop at the flower clock, the ice-wine winery, Niagara by the Lake, the hydroelectric and the cable car. We even did the Maid of the Mist tour.

Niagara Falls

Anyways, it was great fun, and we all enjoyed the splendid summer weather. Toronto has presented itself as a gloriously open-minded city full of people from all over the world, with lots of recreational possibilities, tons of shopping opportunities, and a kick-ass restaurant & coffee scene.

Toronto, not only multicultural, but also super LBGTx friendly
It’s a life. Working on a Sunday afternoon in Toronto

I mainly focused on Toronto’s coffee, food and park infrastructure, which I thoroughly explored with the help of bike sharing and my best friend yelp.

It’s a life. Shopping on a Sunday afternoon in Toronto
Random encounter with weird looking Canadian
Boat trip with Florent & sunset over the Toronto skyline

Towards the end of our stay, Florent and I were bold enough to go for a dinner in the 360 Restaurant on top of the CN tower. We were absolutely stoked by the food, the wine and the view from the rotating restaurant 351 m (1150 ft) above the ground!

Symbol of Toronto’s virility, CN Tower
…where they actually serve most delicious food!
…with a view (and a prize)!
Boston Red Sox visiting (and winning)
ISIMA people standing in line for ramen!

Before heading out, Pascale and I initiated a trip to Toronto’s best ramen place: Sansotei Ramen. Look at us, casually standing in line like some New York hipsters waiting for a Ramen Burger at Smorgasburg. It’s been said that Toronto is New York in the movies – not just there, I’d say, also in our hearts. It’s been a great ISIMA 2014. I’d do it again, anytime.

Cambridge, MA


Cambridge is really beautiful in summer – but it’s also full of tourists! Cohorts of eager parents are walking around MIT and Harvard, many with a sparkle in their eyes, fantasizing that their children may one day be one of the very few kids that actually make it there. Nevertheless, I enjoy spending time in this quirky university town: Kayaking on the Charles River, coffee and sticky buns at Flour Bakery, or Asian-food shopping at H-Mart, always make it worth a trip!

Mass segregation in Palomar 14

The mass function slope is shown as it changes with radius of Palomar 14 (measured from the cluster center). A low value of this slope means that we detect more massive stars at this radius than further out, where the slope is larger. Such a signature is called mass segregation, and is usually a consequence of dynamical evolution of a star cluster.

Matthias Frank, Eva Grebel (both in Heidelberg), and I have recently published another paper on one of our Milky Way’s outer-halo globular clusters. Using archival data from the Hubble Space Telescope and Matthias’ sophisticated photometry tools, we measured the masses of stars within one of the most controversial globular clusters known to us: Palomar 14. With a distance of about 70 kpc (or 230,000 light years) from the Galactic Center, it is one of the most distant star clusters of our Galaxy. It is also one of the least massive clusters, and, rather surprisingly, it is the most extended stellar system without dark matter in the nearby Universe. As such, it has been the subject of numerous observational and theoretical studies since its discovery half a century ago by Sidney van den Bergh. According to Sidney, it was nothing more than a faint smudge on one of the photographic plates of the Palomar Observatory Sky Survey. This unusual fuzziness is due to its large extent: compared to regular globular clusters of the same mass, which show a characteristic radius of 3 pc (10 light years), Palomar 14 has a radius of 46 pc (150 light years)! This was also the motivation for our investigation: in such a loosely bound system you don’t expect the stars to interact much – they stay together as a system, but they don’t exchange energy through fly-bys like all these NASA satellites do with planets when they swing by an inner planet to gain velocity in order to reach a more distant planet/comet/whatever. However, consequences of this energy-exchange process are clearly visible in Palomar 14: the most massive stars tend to sit in the center of the cluster, whereas the least massive ones preferentially orbit further out (summarized in the plot above). This means that either Palomar 14 must have been more than a factor of 10 denser in the past, or it was born with this very unusual configuration. Both scenarios give us a headache, since we haven’t been able to reproduce them in simulations. Even more so, since its distant companion, Palomar 4, has exactly the same issues!

Summer in the City


Apparently, traveling has become an integral part of my life. Coming back from Baltimore early June, however, I managed to stay at home in New York for almost 3 weeks in a row before heading out again. It was amazing! The weather was great, and the City did not reek of trash and rotten rat yet. Of all the fun things I did, cycling around Central Park at sunset was certainly one of the most impressive and most rewarding things to do. Can’t wait to get back on the 6 mile loop!

Hubble TAC


In the first week of June, I went once more to Charm City Baltimore to attend the Hubble Space Telescope Time Allocation Committee meeting. This exclusive event takes place once a year at the Space Telescope Science Institute (STScI), and is meant to sort the wheat from the chaff among the many, many applications for observing time on the Hubble Space Telescope (HST). Since HST is NASA’s flagship satellite and since it’s by far the most successful and powerful telescope available to professional astronomers, demand for observing time is >10 times higher than there’s actually time available (about 5500 orbits of HST around earth per year). To decide who gets to observe with HST, STScI makes a call for proposals once a year. This time we’re in Cycle 22 of this process, and demand is higher than ever (only one year has seen slightly more proposals). After receiving the 1135 applications, STScI invited about 150 American and European astronomers to review and rank them. I’ve been on one out of 14 panels in total, and each panel got to review about 70-80 proposals, i.e. a lot of work. But STScI treats you well. Participants stay in a comfortable hotel close by the institute, they get fed well, and there’s a nice social dinner. Also, you get to meet many people from all across astronomy – new acquaintances as well as old friends. It’s an experience and I’d do it again anytime. Let’s hope HST gets to live another couple of years. But according to the exclusive update on HST’s status we got after the welcome reception, HST will stay in operation until its successor, the James Webb Space Telescope (JWST), is in orbit and fully operational – rumor is that it may even get to see the next decade!



The grande finale of my Euro trip 2014 was the MODEST14 conference in Bad Honnef. MODEST, standing for Modeling and Observing Dense Stellar Systems, is a very specific conference series focussing on my prime field of study: stellar dynamics. The MODEST meetings are always my favorite get-togethers as you get to meet all your friends in this small community, and within a week you have a fresh and complete overview on the current state of the field. This specific edition of the conference series was organized by Sambaran Banerjee who works in the stellar dynamics group of Pavel Kroupa at the University of Bonn. Together with his scientific and local organizing committees he did an amazing job, turning the old mansion of the DFG Physikzentrum into a club house of a debating society. The conference picture above and many more were taken by Fabian Lüghausen. The next big MODEST meeting will be in Concepción, Chile, from March 2-6.



From Heidelberg I went straight to Paris for the weekend. I visited Francesca, my former Italian roommate at Yale, who just moved to Paris for her PhD in biology at the reputable Institut Pasteur. I was shocked to hear that just two weeks ago a post-doc at this institute completely cracked, and went berserk in the lab. In his frenzy, he ruined several mice experiments, and even burnt 600 lab mice! I guess that’s how crazy the pressure in science can get. You get a career or you fail in life, that’s the mentality. Anyways, the weekend was lovely and I got to see Paris again from a stress-free point of view. Especially in Paris it’s so much more relaxed when you’ve seen all the major sights and can focus on the more enjoyable sides of the city. Clearly, I’m talking about the boulangeries here, which are kind of the independent coffee shops of Paris. Croissants, baguettes and macarones, je vous aime!