A Summer at the South Pole

Much like bumper cars, galaxies fly about the center
and smash into one another. As a demonstration,
the large blue galaxyon the left, nicknamed
the guitar galaxy,is torn apart as it collides
with another member of the cluster.*In the last two posts, I talked about solar systems and galaxies, you know, the really small stuff. Personally, I'm interested in the cosmological behemoths: clusters of galaxies. In fact, I studied these behemoths for five years in graduate school.

As the name would imply, a cluster of galaxies is a large system of galaxies, much like a solar system is a system of planets and a galaxy is a system of stars. In the largest clusters, there are thousands of galaxies, each trapped by the enormous gravity of the entire cluster. The largest cluster members are among the very first galaxies to have formed in the universe. Living in the rich cluster environment, they’ve had a lot of time to grow through collisions with other cluster galaxies, and are also among the largest galaxies in the universe.

There are probably around 1,000 known galaxy clusters. All of the known clusters have been discovered using well-established techniques, such as just taking pictures through a telescope. However, we’ve only managed to search a small bit of the universe, and we believe there are hundreds of thousands still out there, waiting to be discovered.

For three summers, I searched for new clusters using two California telescopes: the BIMA array in Hat Creek and the OVRO array near Bishop. With all those massive clusters, you'd think it would be a breeze to find them. For better or for worse, I was using a fairly new technique which hadn't really been developed to the point of routine use and I came up empty-handed.

This new technique targets a unique signature of galaxy clusters, the Sunyaev-Zel'dovich effect, or as it is more affectionately known, the SZ effect. The SZ effect describes how a galaxy cluster appears silhouetted against the glow of the big bang known as the cosmic microwave background, or CMB. I'll cover this in a later post, but if you are anxious for more details, feel free to ask.

Construction at the South PoleNow, technology has advanced so far that there are several telescopes dedicated entirely to looking for clusters of galaxies using the SZ effect. One of these is the new South Pole Telescope, located at the very bottom of the planet and just commissioned this year. Using this telescope, scientists from eight different institutions (including my old boss at UC-Berkeley) will outdo my 5-year doctoral thesis project every two and a half minutes. By late 2008, they will have studied 20,000 times more universe and should find more than 10,000 new clusters. Maybe I should have worked harder in graduate school…

Standing seven stories tall with a diameter of over 30 feet, the telescope weighs almost 600,000 pounds. It was constructed in much nicer climates and then flown down to the South Pole one piece at a time on an old military cargo plane. By the time the last nut and bolt arrived at the site, the plane had made over 50 round trip flights.

The telescope was pieced together at the South Pole during the Austral summer, running from December till February at a balmy -30 to -40 degrees Fahrenheit. With a population of 18 scientists for this project and 240 people from other projects, summer is the busy time at the South Pole. However, all of the sane people flee before the sun sets for six months of darkness, leaving only "winter-overs" behind for the cold season (I just looked at the weather and it’s currently -83.9 degrees). This year, there will be 54 winter-overs, two of whom will be running the South Pole Telescope as it searches for new clusters.

After the telescope construction was completed, the last of the summer crew worked like mad to test the instrument before they had to head back home. This in itself is nearly as much work as constructing the telescope in the bitter cold. For example, the camera operates at a temperature of 0.25 Kelvin - any warmer and the sensors don't work. You have to keep an eye on every wire and every cable just to get the camera to be this cold. Then they went through several stages of calibrating the instrument, making sure they could reproduce what they saw when testing the camera in the lab in Berkeley.

As time was running out, they still hadn't actually looked at anything on the sky. They begged and gnashed their teeth for more time. With a little luck from the weather and a soft-hearted commander from the Air National Guard, they got one extra day to observe their first astronomical objects, starting with the planets in our solar system. Now, the next step is to find some of those elusive clusters.

Panoramic view of the South Pole Telescope

As I sit and re-read this posting, I realize that I left out one crucial ingredient - Why the South Pole??? Well, although it is a crazy place to work, there are quite a few advantages of building a telescope there rather than some tropical paradise like Tahiti.

Any ideas what makes all the effort in such a harsh climate worth the hassle?

Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and
development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.

* Credit & Copyright: Jean-Charles Cuillandre (CFHT), Hawaiian Starlight, CFHT Most of the galaxies in this image are part of the massive cluster Abell1185.