Tag Archives: aifa

Signs of hidden matter

4U182030
Comparison of different observational data (rows) to three different cluster models (columns) of the globular cluster NGC 6624. The observed accelerations of a low-mass X-ray binary and of three pulsars (bottom row) tell us that the density of matter (top row) in the center (small radius R) has to be higher than what we see in the form of stars.

When we look into the night sky we are fooled by the bright and sparkling stars, and we think they make up most of the matter in the Universe. Among astronomers that’s commonly believed to not be true, since observations tell us that a significantly larger amount of mass fills the Universe in the form of dark matter. What dark matter is, and whether it exists at all, is difficult to answer and no one has found a definite answer yet. However, there are other forms of matter that hide from our naked eyes, or even from our large armada of telescopes. Planets, brown dwarfs, low-mass stars, neutron stars, white dwarfs and black holes are all emitting barely any electromagnetic radiation (a.k.a. light). Thus, only in very few, and nearby cases we can actually observe these objects. For most parts of the Universe, this hidden matter remains unseen and we have to add a certain amount of dark mass to the mass we see in stars based on the best of our knowledge.  Continue reading Signs of hidden matter

Advertisements

MODEST14

IMG_4039_small

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.

Universität Bonn

20140526-120117-43277257.jpg

It was fun to come back to my Alma Mater in Bonn and give a colloquium at the Argelander-Institut für Astronomie. After my talk, I got great feedback from Andreas Brunthaler: the maser people from Harvard and the Max-Planck-Institut für Radioastronomie apparently get the same results for the Galactic center distance as me! This makes it an agreement between three independent methods.  Continue reading Universität Bonn

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