UO scientist boosts search for Crab Pulsar's gravitational waves

Robert Schofield in his lab on the UO campus

Mug shot also available                      (Photo by Jim Barlow)

EUGENE, Ore. -- (June 2, 2008) -- Detecting elusive gravitational waves from a rapidly spinning neutron star 6,500 light years away involves narrow fine-tuning here on Earth -- not much different, conceptually anyway, from tuning in a faint radio station.

Complicating that problem, the spinning pulsar produces gravitational waves at 59.6 hertz (cycles per second), very close in frequency to large 'static' produced by common 60-hertz electrical systems.

The work of a University of Oregon scientist helped eliminate the interference and pave the way for today’s announcement by the international LIGO (Laser Interferometer Gravitational-Wave Observatory) Scientific Collaboration.

The LIGO researchers report that gravitational signals from a neutron star known as the Crab pulsar in the distant Crab Nebula are too faint to play an important role in slowing the pulsar. (See the LIGO news release) The Crab pulsar's rotation rate is decreasing rapidly compared to most pulsars, indicating that it is radiating energy at an enormous rate. The mechanism for this decrease is unknown, but gravitational radiation is now eliminated as the leading contributor.

UO physicist Robert Schofield's 'crab-protection' techniques were a critical element of this measurement. To get the desired sensitivity, scientists had to eliminate 60-hertz interference, or noise, disturbing LIGO's huge interferometer. "The solution came in the form of Schofield's techniques," said LIGO scientist and UO particle physicist James E. Brau, the UO's Knight Professor of Natural Science.

"We try to detect the crab by observing the motion of test masses," Schofield said. "If some noise source associated with 60 hertz causes our test masses to move around by more than about one one-thousandth of the diameter of a proton, then this motion obscures any smaller motion produced by the crab and so makes us less sensitive."

Such movement can occur when circuits are turned on and off, producing magnetic transients that push the magnets just enough to alter sensitivity. Another source is the vibration of many electric motors, such as those in air-conditioning systems and sump or vacuum pumps, Schofield said. They can shake the ground and move test masses by just enough to throw off measurements.

"My crab-protection job was a lot of detective work, finding out what was causing the noise that reduced crab sensitivity, and shutting down, mitigating or modifying the frequency of the source," he said. "Sometimes offending motors were in buildings hundreds of meters away. Even transients in 500-kilovolt power transmission lines two kilometers away affected us via magnetic fields."

For the project, Schofield worked at the LIGO facility in Hanford, Wash., where he spends two weeks of each month on physics projects. Back on the UO campus, he pursues research related to biology. Schofield is part of UO's LIGO group, which is led by Brau and physicist Ray Frey.

Schofield, Brau and Frey are members of the UO's Center for High Energy Physics.

About the University of Oregon
The University of Oregon is a world-class teaching and research institution and Oregon’s flagship public university. The UO is a member of the Association of American Universities (AAU), an organization made up of 62 of the leading public and private research institutions in the United States and Canada. Membership in the AAU is by invitation only. The University of Oregon is one of only two AAU members in the Pacific Northwest.

Media Contact: Jim Barlow, director of science and research communications, 541-346-3481, jebarlow@uoregon.edu

Sources: Robert Schofield, physics senior research associate, 541-346-4783, rmss@conch.uoregon.edu; Jim Brau, professor of physics, College of Arts and Sciences, 541-346-4766, jimbrau@uoregon.edu