Tag Archives: lmxb

Signs of hidden matter

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

Universität Bonn


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