The Gravity Signature at LIGO/VIRGO at Quarter Century


Gravitational-Wave Hunt Restarts—with a Quantum Boost

“Detailed data on space-time ripples are set to pour in from LIGO and Virgo’s upgraded detectors”


Inside the LIGO gravitational-wave detector in Hanford, Washington, engineers install hardware upgrades necessary for the facilities latest observing run. Credit: Jeff Kissel, LIGO, Caltech and MIT

The hunt for gravitational waves is on again—this time assisted by the quirks of quantum mechanics.

Three massive detectors—the two in the United States called LIGO and one in Italy known as Virgo—officially resumed collecting data on April 1, after a 19-month shutdown for upgrades. Thanks in part to a quantum phenomenon known as light squeezing, the machines promise not only to spot more gravitational waves—ripples in space-time that can reveal a wealth of information about the cosmos—but also to make more detailed detections. Researchers hope to observe as-yet undetected events, such as a supernova or the merging of a black hole with a neutron star.

The run, which will last until next March, also marks a major change in how gravitational-wave astronomy is done. For the first time, LIGO and Virgo will send out public, real-time alerts on wave detections to tip off other observatories—and anyone with a telescope—on how to find the events, so that they can be studied with traditional techniques, from radio- to space-based X-ray telescopes. The alerts will also be available through a smartphone app. “Astronomers are really hungry,” says David Reitze, a physicist at the California Institute of Technology in Pasadena and director of the Laser Interferometer Gravitational-wave Observatory (LIGO), which made the first historic detection of gravitational waves in 2015.


The increased sensitivity will enable the detectors to better distinguish signals from the constant background of noise—providing physicists with more detail on the waves. This could in turn allow for precise tests of Albert Einstein’s general theory of relativity, which predicted the existence of gravitational waves.

Future detections should reveal secrets about black holes that are in the process of merging, such as how fast they spin and in which direction, says Ilya Mandel, a theoretical astrophysicist at Monash University in Melbourne, Australia. “Maybe we can start teasing out some information about whether they preferentially align,” he says.

If the black holes’ rotational axes are parallel, that would suggest they have a common origin and started out as two stars orbiting together. Conversely, spins that are randomly aligned imply that the black holes formed separately and then began to orbit each other later on.


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