Tag Archives: hpc

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


Palomar 4

This website was never intended to be a science blog, but since science is an essential part of my life – with all its ups and downs, kinks and quirks, bores and funzies – I shouldn’t neglect it here! Today, a paper of me and my dear collaborators from Iran, Elham Hasani Zonoozi and Hosein Haghi appeared on astro-ph.

Mass function slope versus cluster radius
Slope of the stellar mass function versus projected radius from the cluster center for the observations of Palomar 4 (red) and for our best-fitting model (black). The goal was to find a model that reproduces the observed trend of the massive cluster stars being more centrally concentrated, which can be seen from the slope being below its nominal value (dashed line) in the center, while being above that line in the outer parts of the cluster.

Continue reading Palomar 4



Blue hour’s sweet light was looming over Riverside Church when I left the astronomy department yesterday. Meanwhile, New York was turning into a huge slush puppie as the temperatures got milder. I felt like I had earned myself an afterwork beer with fellow Columbia astronomers and visiting ex-Columbiast Taka Tanaka. After being super productive during the last weeks, my Palomar 5 project is finally coming to an end! All I have to do now is wait for Yeti to deliver results. No, I did not hire Jaroslav Haas to compute likelihoods for me. Yeti is Columbia’s new >1600 core supercomputer, which has been inaugurated end of last year. I’ll post some results as soon as I get them, which will be in about one week. I’m excited, it all looks very, very promising.