All is quiet on the LIGO front.
Following the detection of gravitational waves in September 2015, the thousand or so scientists who make up the Laser Interferometer Gravitational-Wave Observatory—or LIGO—collaboration probably deserved a rest. The groundbreaking discovery confirmed Albert
Einstein’s long-standing theory of general relativity and resulted in several scientists on the team receiving the 2017 Nobel Prize in Physics.
The silence is strategic: the twin billion-dollar LIGO detectors in Louisiana and Washington (along with LIGO’s European companion, Virgo) are undergoing upgrades. When the detectors are back in business a year from now, LIGO will have the capability “to see events in a roughly eightfold larger volume of space,” says Carleton physics professor Jay Tasson, who joined Carleton’s LIGO cohort in September 2016. “These major observations may become quite routine. How are we going to streamline our processes for analyzing these events? What are the new things we can test and learn about general relativity and astrophysics? We’ve got less than a year to get ready.”
After a series of headlining achievements—from the first gravitational wave detection in 2015 to last year’s observations of gravitational waves caused by colliding neutron stars and a binary black hole merger—it’s hard to fathom that LIGO could become even more productive after its upgrade. “I’ve never worked so hard in my life,” says Carleton physics professor Nelson Christensen. “On the other hand, I’ve never been so excited. [The LIGO scientists] have worked our entire lives on these concepts and we never thought we’d get to this point.”
Carleton has been a member of LIGO since 1999. However, LIGO’s recent discoveries owe a lot to Carleton physics professor Joel Weisberg, whose 1980s research on binary pulsars provided the first observational evidence for the existence of gravitational waves as predicted by general relativity. Carleton also is a leader among undergraduate liberal arts colleges for the number of its professors, alumni, and students who are working in the collaboration—with around 20 of them contributing authorship to published papers.
“I always talk to Carleton students about being on the front lines of science, and with LIGO, we really are,” says Christensen, who has spent the past year in France working with LIGO and Virgo. “The results are among the most exciting things to ever happen in science and physics. We’re literally figuring out the universe.”
Laser Interferometer Gravitational-Wave Observatory (LIGO)
Origin: Completed in 1999; first search for gravitational waves began in 2002
Claim to fame: The world’s first direct detection of gravitational waves on September 14, 2015. The gravitational waves were generated by two black holes colliding and merging into one nearly 1.3 billion light years from Earth.
Locations: Livingston, Louisiana, and Hanford, Washington. The two locations, some 2,000 miles apart, were chosen because of their isolation from sound and people. LIGO also collaborates with Virgo, a detector near Pisa, Italy.
Measurements: Two L-shaped detectors—the largest precision optical instruments ever built—feature 2.5-mile-long vacuum chambers. Each chamber encloses as much volume as 11 Boeing 747-400 commercial airliners.
Sensitivity: Can identify a change in distance between its mirrors 1/10,000th the width of a proton, or the equivalent of measuring the distance to the nearest star to an accuracy smaller than the width of a human hair
Operated by: California Institute of Technology (Caltech) and Massachusetts Institute of Technology (MIT)
Funded by: National Science Foundation
Membership: More than 1,000 scientists from nearly 100 institutions and 18 countries
LIGO Detector in Livingston, Louisiana
LIGO’s two massive L-shaped detectors—or interferometers—are located in remote, sparsely populated areas in Louisiana and Washington. Since LIGO doesn’t need to collect light from stars or other objects in the universe, it doesn’t have the “eyes” typical of astronomical observatories. The 2.5-mile-long detectors essentially act as antennae and are so sensitive that they can “feel” vibrations from thousands of miles away. The tubes are protected by a 10-foot-wide, 12-foot-tall concrete enclosure.
Laser and Vacuum Equipment Area in Hanford, Washington
As explained in Science magazine, a passing gravitational wave will generally stretch the interferometers’ two 2.5-mile-long tube arms by different amounts. So scientists bounce a laser beam back and forth in the arms to detect the slight stretching. To be confirmed as real, the resulting signal must show up in both detectors, which filter out any earthly vibrations that might affect the detectors. This photo shows a bird’s-eye view of LIGO’s laser and vacuum equipment area, which houses the prestabilized laser, beam splitter, input test masses, and other equipment.
Spiraling Black Holes
LIGO scientists have discovered that black holes merge more often than previously thought. They’ve used gravitational wave detections to confirm the existence of binary black holes and to measure the masses of black holes 30 times larger than our sun. This artist’s conception shows two merging black holes similar to those detected by LIGO.
Gravitational Wave Model
Historically, scientists have relied primarily on electromagnetic radiation (visible light, X-rays, radio waves) to make observations. Gravitational waves—ripples in spacetime—are “an entirely new tool used to get information about remote events in the universe,” says Carleton physics professor Jay Tasson. They help astrophysicists confirm—and acquire more details about—what they’ve been seeing with traditional telescopes. This illustration shows the merger of two black holes and the gravitational waves that ripple outward as the holes spiral toward each other. In reality, the area near the black holes would appear highly warped and the gravitational waves would be difficult to see directly.
Colliding Neutron Stars
Thanks to gravitational wave detections, LIGO scientists have confirmed that when binary neutron stars merge, they cause bursts of gamma radiation, as shown in this illustration. Scientists speculate that neutron star collisions could be the origin of some common heavy elements, such as gold and silver.
Photos courtesy of the California Institute of Technology