Einstein's Cosmic Symphony

Building a LIGO Supercomputer

Five years ago, Professor Duncan Brown joined the physics department. As a graduate student at the University of Wisconsin-Milwaukee (UW-M), Brown wrote a major piece of the gravitational-wave search software used by LIGO. He subsequently spent three years working with Caltech’s Kip Thorne who, alongside Weiss, is a key player in gravitational-wave research and in the LIGO collaboration. Brown, an NSF CAREER award recipient and Cottrell Scholar, was the principal investigator in a project to build a LIGO supercomputer at SU. Funded by the NSF and The College of Arts and Sciences, the cluster is housed in the new Green Data Center on South Campus. Collaborating on the project were co-principal investigators Tomasz Skwarnicki, professor of physics; and Christopher Sedore, associate vice chancellor for academic operations. The SU supercomputer is one of three LIGO computing centers that join with the LIGO Laboratory's main computing center to provide resources for LIGO scientists worldwide. The other two are located at UW-M and the Albert Einstein Institute for Gravitational Physics in Germany.

The SU group is also taking the lead on projects to improve the gravitational-wave search software for Advanced LIGO (see related story: Clangs and Bangs) and develop new technologies that will increase the sensitivity of LIGO instruments beyond what is currently possible. In addition to Saulson and Brown, the group includes physics professor Stefan Ballmer, who is building a mini-LIGO prototype at SU to explore new ways to enhance the sensitivity of LIGO instruments (see related story: Squeezing Light). Computing specialist Peter Couvares, two postdoctoral researchers, seven graduate students, and two undergraduates are also involved in SU’s LIGO research group.

About Mirrors and 'Jiggle'

At the core of LIGO technology is the laser interferometer, which uses a beam of light and a photodetector to sense gravitational waves. Specifically, it measures the distance light travels in a vacuum between suspended mirrors located at either end of four-kilometer-long, L-shaped “arms.” Gravitational waves and other vibrations and noise cause the mirrors to move a tiny bit—less than the diameter of a proton. The movement changes the distance light travels between the mirrors, which is measured by the photodetector and converted into an electrical signal—the musical notes of the cosmos.

One noise that plagued the initial LIGO instruments was a barely perceptible jitter in the glass mirrors caused by friction from the movement of silicon and oxygen atoms in the glass. The jitter was invisible to the naked eye—and most instruments—but loud enough to cover the sound of gravitational waves. “We needed to significantly reduce this noise, but the only trick we knew was to replace the glass with sapphire, which has very low friction,” Saulson says. “I spent my first 10 years at SU trying to learn whether there was any way you could buy, treat, or hold a form of glass that would have the friction level of sapphire yet retain the properties we required—and we found it.”

Saulson’s team discovered an extremely pure form of silicon dioxide that has a very low internal friction. It was a significant accomplishment that required the team to develop a way to measure internal friction before they could begin to analyze different types of glass. Saulson has now moved to new areas of LIGO research, one of which is to improve the gravitational-wave search software for Advanced LIGO. “As cool as the glass stuff is, I really want to find gravitational waves in the data,” Saulson says. “SU is one of the leading institutions in the country in LIGO. We should all take pride in our role in building very important pieces of the LIGO effort.”