About 130 million years ago in the distant galaxy, two neutron stars spiraled toward each other and merged. This violent event initiated ripples in the fabric of spacetime — gravitational waves — which propagated through space at the speed of light.
On Aug. 17, 2017, at 5:41 a.m. Pacific Time, those waves arrived at Earth and were picked up by three intricate, kilometers-long gravitational wave detectors, one of which is in Washington state. This gravitational wave signal briefly preceded a faint light signal from the same event, which was picked up by several Earth- and space-based astronomical observatories. This scientific feat was announced Oct. 16 by the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO) and Europe-based Virgo detector, along with partners at approximately 70 observatories.
“Today’s announcement marks the first time that we have detected gravitational waves from the merger of two neutron stars,” said Joey Shapiro Key, assistant professor of physics at the University of Washington Bothell. “In addition, this is the first time that other observatories detected electromagnetic waves emanating from the astronomical event that generated these gravitational waves.”
Key is one of three UW faculty members who are part of the LIGO-Virgo collaboration, along with professor Jens Gundlach and acting assistant professor Krishna Venkateswara, both in the Department of Physics at the UW’s Seattle campus. Gundlach and Venkateswara work on instruments to improve the accuracy of detectors. Key and her group analyze data from detection events.
“This is a huge, collaborative effort — bringing together scientists from across the globe to measure events predicted by Einstein’s theory,” said Gundlach. “Einstein, however, was wrong in claiming that it would be technically impossible to detect gravitational waves.”
Previously confirmed detections of gravitational waves in 2015 and earlier this year all came from mergers of black holes, events that emit no visible light. But since the neutron star merger detected on Aug. 17 also emitted electromagnetic waves, Earth- and space-based observatories picked up signals such as light emissions and gamma ray bursts. It marks the first time that a cosmic event has been detected using both gravitational waves and electromagnetic waves.
LIGO consists of two ultrasensitive detectors in the United States, one at Hanford, Washington and the other in Livingston, Louisiana. Gundlach joined the LIGO team to help those detectors pick up the fantastically small movements caused by gravitational waves, which is no small task given the dynamic environment on our planet.
“Anything that causes drag on the instruments in the detector or affects their precision in any way creates ‘noise,’ which can obscure the tiny signals left by gravitational waves,” said Gundlach.
Gundlach’s group studied subtle disturbances to the LIGO detectors — which would limit the sensitivity of the detectors — and appeared to be caused by residual air molecules in the vacuum chambers or interference from electrostatic sources. Venkateswara joined Gundlach’s team as a postdoctoral researcher in 2011 to develop methods to reduce interference caused by wind, which could blow against the building and obscure signals from gravitational waves.
“The LIGO detectors have had this long-standing problem related to ‘tilt’ from wind action,” said Venkateswara. “The instrumentation within the detectors is so sensitive that — even though they operate indoors and in a vacuum — wind blowing outside the building caused the detector to malfunction.”
Venkateswara, Gundlach and doctoral student Michael Ross invented novel devices that could accurately pick up imperceptibly small tilt of the ground. From 2014 to 2016, Venkateswara and Ross then installed, maintained and tested these sensors at the LIGO detector at Hanford, ensuring that ground tilt could be filtered out of detector measurements. These efforts improved the accuracy and efficiency of observations at Hanford. Now, Venkateswara is preparing to install similar sensors at the Livingston detector.
That will mean more data to analyze for Key and her group at UW Bothell, which includes researcher Matt DePies and students Andrew Clark, Holly Gummelt, Paul Marsh, Jomardee Perkins and Katherine Reyes.
The Bothell team works on estimating the physical parameters of gravitational wave data from the detectors, helping to determine their origin in the universe, strength and other properties. They also develop analysis tools to filter out noise from the detectors to improve data quality. Marsh spent this past summer at the Hanford LIGO detector working with the control systems on site.
“These are incredibly precise instruments, but they require a great deal of maintenance, calibration and upkeep,” said Key. “And even after the data come out, there is more work to be done before we can understand the observations themselves.”
These observations add new dimensions to astronomical events that were previously only observable by electromagnetic waves, said Key. Direct — and increasingly precise — detections of gravitational waves also give scientists new opportunities to measure phenomena that, up until recently, were only theories on paper or indirect observations, added Gundlach.
“These collaborations are an ongoing and expanding process,” said Gundlach. “More detectors, better instruments and improved analysis tools — it all gives us so much more insight into figuring out our universe.”
