LIGO Receives $205 M from NSF – Hobart and William Smith Colleges \
The HWS Update

LIGO Receives $205 M from NSF

Professor Penn’s research at the heart of the new observatory’s design When you jump on a trampoline you will notice the canvas stretch and curve beneath your feet. With each bounce a vibration is created as a ripple in the trampoline fabric. Amazingly, the fabric of space and time is not unlike that trampoline. It curves due to the presence of your mass, and if you jump (accelerate) a small wave, called a gravity wave, is created in the “fabric” of space-time. Unfortunately, the wave you (or any earthbound accelerating object) create in a trampoline-sized piece of space-time is unimaginably small — more than a billion, billion times smaller than a proton. To make a really big gravity-wave you need star-sized masses accelerating at rates that would rip most stars apart. A few events in the universe can create these big waves: the inspiral and collision of black holes or neutron stars, the supernova explosion that annihilates a large mass star, or the first few seconds of the Big Bang explosion that created the universe. These energetic events can produce a gravity wave that, when it reaches LIGO, may be only one ten-thousandth the diameter of a proton. Measuring these waves may seem like an impossible task, but that is exactly what Assistant Professor of Physics Steven Penn and his students are trying to accomplish as part of the Laser Interferometer Gravitational-wave Observatory (LIGO) project. LIGO has two observatories, one in Hanford, Wash. and one in Livingston, La., that each study a large square of space-time with a side measuring 4 km (2.5 miles). These facilities use a laser interferometer to sense tiny vibrations that stretch that space-time by a mere 10-18 m, or one one-thousandth the diameter of a proton. Amazing … but not yet good enough. “From the beginning of the LIGO project, there were plans for an Advanced LIGO,” says Penn, referring to the second stage of the LIGO project. When LIGO was proposed the technology did not exist to measure vibrations as tiny as the largest anticipated gravity waves. Therefore Initial LIGO was the first phase of the project, charged with building the observatories and then operating them for a year at the 10-18 m sensitivity. Those tasks were completed successfully in October 2007. During the Initial LIGO phase, Penn and dozens of other LIGO scientists were busily researching the technologies required to build Advanced LIGO. Penn’s work on low noise optical materials was key to the successful development of the Advanced LIGO test mass mirrors. The relative motion of these mirrors is used to detect the space-time stretching due to a gravity wave. The “standard candle” of gravity waves is the inspiral of two neutron stars, or BNSI event. Initial LIGO can see a BNSI if it occurs within about 50 million light-years. Since galaxies are separated by 3-4 light years, LIGO can see about 100 trillion stars. But BNSI events are extremely rare. “LIGO allowed us to see gravity waves from a BNSI about once every 3 to 10 years,” said Penn. “That is why we need Advanced LIGO. Advanced LIGO has the sensitivity to see 10 times farther. When the observatory reaches full operation in 2015, we predict that we will detect a few BNSI events each week.” “My role in Advanced LIGO along with my four students – Raghuvir Kasturi ’10, Christine Luongo ’10, Paul Stevens ’10 and Matthew Scanlon ’10 – is in three areas,” explained Penn. “First, we are investigating ways to reduce the thermal noise in the test mass mirror substrates. Second, we’re working on reducing the thermal noise in the mirror coatings. Lastly, we’re improving the wire suspension of the current system for a possible intermediate upgrade to the mirror suspensions.” Penn is proud of his research and his students. “Many people assume that high level experimental physics research cannot be done at a small liberal arts college,” says Penn. “But we’re proving that assumption is wrong. Our resources are more limited, but we have the same focus and determination as any large university research group.” “We perform our research on the LIGO mirrors,” said Penn, “but we never lose sight of the real goal: to detect gravity waves. Doing so will verify the last missing prediction from Einstein’s General Theory of Relativity. It will also open a new window on our universe as we see it, for the first time, using gravity waves.” That is an accomplishment of, well, cosmic proportions.