Globular Clusters

Globular clusters are large (>100 ly diameter), spherical groups of stars that are bound to one another by a very strong gravitational attraction. They are fairly commonly found (at least 150 are known in our galaxy) and contain many dense, old stars (10 billion+ yrs). The stars within a globular cluster have highly eccentric orbits with high radial velocities. Some clusters are close enough that we can study individual stars within them; a great asset indeed!

Globular clusters are found in the part of the galaxy with hot, ionized gas, known as the halo. What makes globular clusters interesting is the sheer amount of stars (10,000+), all of which are about the same age and all located within a fairly condensed region of space. The stars range from variable, white dwarfs, neutron stars, pulsars, etc. though most are variable. Generally, the stars in globular clusters are not giants or supergiants due to their age (giants and supergiants have fairly short lifespans, as far as stars go). This also explains the presence of neutron stars in globular clusters, indicating that perhaps at one time, giants or supergiants did exist in the clusters but died out (this is just my guess). Most of the stars in the cluster are comprised of mainly hydrogen and helium, which is also a clue to indicate the star's age (the older a star is, it will have a great composition of hydrogen and helium, as opposed to a younger star which will be composed of a greater diversity of elements).

(Photo taken from sciencephoto.com)

(H-R diagram for the globular cluster M5. Notice the values for the luminosity and B-V, putting these stars well out of the main sequence range. Photo source)

Additionally, all globular clusters are of about the same age and tend to contain about the same amount of stars.  It is thought that globular clusters have survived early galaxy collisions due to their high gravitational attraction, disallowing for the stars to be destroyed by the changing gravitational forces that occur during galaxy collision. This means that while other stars and star clusters were being destroyed because they couldn't handle the changing gravitational forces, globular clusters were able to survive because their collective gravitational force with one another left them relatively unaffected by the changing conditions.

Globular clusters are great for astronomers to study because of their age and number of stars present. It helps give an idea about how stars evolve and also tells us what stars were like in the early universe, as well as giving us and indication about the age of the universe itself. Additionally, some globular clusters may contain black holes; these black holes give us information about all sorts of things, including star and galaxy formation, as well as black hole formation (whether they are formed all at once, or slowly over time). Also, since globular clusters are so old, this indicates that the black holes are rather ancient as well.

Globular clusters are a fascinating and important part of our universe and we are lucky to have them around!

What Astronomers Do

I have a hard time explaining my understanding of what astronomers do when I am asked by family or other people I know. The first and most obvious answer I give is that they observe things, usually stars, in the sky so they can later study them. Most people, when I say this, probably don't realize that there are a lot of different kinds of stars that are formed and behave differently. The differences in these stars make them interesting for study. Why should one star form one way and another star form a completely different way? Learning about the forming conditions are just one jobs of the astronomer. Other astronomers are interested in how things first started billions of years ago. Learning about how other galaxies were formed and how they work gives us insight about our own galaxy. Then there is the question of what is space itself made of? Before the 20th century or so, astronomers thought space was made up of the aether but that was found to be false. The constant inquiry of astronomers has lead to a more accurate understanding about the very nature of space itself.

Those are just a few of the things that come to mind immediately when I am asked about what astronomers do. Of course, one can't think about astronomy without thinking of telescopes and pretty pictures as well. If most people don't really know what astronomers do then they also have less of an idea about how the telescopes work as well. So knowing how to operate the telescope is also a part of what astronomers do, at least if they want to collect any data.

Astronomers also employ math to come to conclusions about their data, or to support new ideas that are in the process of becoming theories. I always have to remember not to overlook this aspect when describing astronomy to other people, that astronomy is not just collecting data with a bunch of cool technology.

Although for me, the hardest part about trying to explain what astronomers do is to try and put it in some sort of context that most people will care about or be able to relate to. For most people, understanding how stars form and such is rather useless knowledge; it's (most likely) not going to cure cancer and it doesn't help run a business. To me though, learning and developing a better understanding of our universe is more important than managing a business. After all, we are all living in this giant expanse of space and to limit our interests to the mundane, everyday activity of ourselves is to miss the point of what it means to be inquisitive beings trying to expand our knowledge.