Week 1: Galaxy Density

Today during class, I mistakenly heard Prof. Siana make a comment that the Milky Way was a particularly dense galaxy. Although I misheard (he said that galaxies, in general are dense compared to space), this prompted me to ask him afterward about the measurement of galaxy density. The methods he described to me, in a quick recap, involved using the make-up of stars in the galaxy (by percent of different stars in the galaxy) and the luminosity of the galaxy. From that, astronomers can extrapolate how roughly how many massive stars are in the galaxy. Then, using the size (as determined by parallax measurments), they can determine the density of the galaxy.

There are some major innacuracies in this, of course; some objects in the galaxy are contributing to the overall mass of the galaxy, but are not inherently luminous. The largest of these, it seems, would be dark matter clusters. This can be slightly corrected by gravitational lensing. In my research for this blog, I came across an article from 2013: a paper highlighting techniques used by astronomers at numerous research institutions collaborating to measure data on the density of dark matter distribution among multiple galaxies.What they saw lined up well with current CDM, or cold dark matter, theories.

The methods, which are more comprehensively discussed in the linked article, seem to present improved ways on accounting for the density of dark matter when dealing with galaxy density.

Here is a link to the academic article, and a link to the article that led me to it. Hope everyone is having a good start to school, and good luck on the assignment.

-Aaron

P.S. Just a random occurrence. As I was re-doing problem four tonight (on Comet Lovejoy), I was shuffling through old music, when a song by the same name started playing. I thought it was a weird coincidence. I have it linked here, for any of you who would appreciate random jazz/hip hop instrumentals. I don't think it has anything to do with the comet itself, but it is still a good song. The whole album is pretty good, actually, if you are interested.