In my first year at Columbia I worked with grad student Sarah Pearson on an idea that Kathryn Johnston had while trying to find an orbit for Palomar 5 in a Law & Majewski potential. Wait what? Who’s Sarah, who’s Palomar 5, and what is a Law & Majewski potential?
Palomar 5 is a globular cluster in the halo of our Galaxy, the Milky Way. It is about 12 billion years old and consists of roughly 30,000 stars. The star cluster can be seen within the footprint of the Sloan Digital Sky Survey. But even more fascinating is that we can also see a stream, consisting of at least as many stars, stretching out from the cluster along its orbit. This stream – there are actually two, one in the leading direction and one in the trailing direction – spans about 23 degrees on the sky, while being on average half a degree wide. That’s about the size of 50 full moons! Continue reading Stream fanning→
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→
During Steffen’s time at Columbia in February this year, we were talking a lot about erosion of globular clusters by the gravitational field of their host galaxy. Steffen came up with the great idea that this erosion process may be responsible for the observed variations of the number of globular clusters around different kinds of galaxies. In general, you see that galaxies with a small total mass will have a small number of globular clusters. But if you divide the number of a galaxy’s globular clusters by the mass of the galaxy, you will not get a flat distribution as naively expected. Instead, you get a U-shaped distribution, telling you that very low-mass galaxies and very high-mass galaxies have more globular clusters than average, whereas intermediate-mass galaxies have suspiciously few clusters. Why should those galaxies be any special?? Continue reading Specific Frequency of Globular Clusters→