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LIGO cranks up the sensitivity to sniff out gravitational waves

The instrument that proved Einstein right is back

The US ultra-sensitive space science project, which first proved the existence of gravitational waves, is back after three years of upgrades and maintenance made it 30 percent more sensitive.

Astroboffins behind the LIGO – or Laser Interferometer Gravitational-Wave Observatory – say the increased sensitivity means the detectors will pick up gravitational wave signals at a higher rate, detecting a merger every two or three days.

The project kicked of a new run of observations, dubbed O4, this week, with Japan's KAGRA detector set to join in months and Europe's Virgo detector to become part of the data gathering later this year.

The US LIGO team has two detectors, one in Hanford, Washington, and another in Livingston, Louisiana. It is led by physicists at Caltech.

Albert Lazzarini, deputy director of the LIGO Laboratory, said: "Our LIGO teams have worked through hardship during the past two-plus years. Our engineering run leading up to the official start of O4 has already revealed a number of candidate events, which we have shared with the astronomical community. Most of these involve black hole binary systems, although one may include a neutron star. The rates appear to be consistent with expectations."

LIGO's upgrade was expected to cost around $35 million and allow scientists to get more detailed physical information from the data in the hope of offering a better test for Einstein's general theory of relativity.

The first gravitational wave signals were detected in 2015, with the results first published in 2016. The 15-year experiment required incredibly sensitive apparatus to pick up tiny fluctuations in spacetime caused by distant cosmic impact.

Since then, around 90 gravitational wave events have been observed by LIGO, Virgo and KAGRA, including the merger of a black hole and a neutron star – not once but twice in the same month in 2021.

The 2015 discovery was just the start of a new field of research, Professor Mark Hannam, part of the Cardiff University team involved in that important breakthrough, explained in a lecture for The Register in 2018.

In the widely accepted theory of general relativity (1915), Einstein proposed that space-time would be warped by large masses. The theory also leads to the prediction that collisions between massive objects would cause ripples or waves in space-time, but for decades many scientists thought them too weak to detect. The LIGO detectors have been able to prove them wrong by splitting laser beams over separate right-angled paths of 4km, to be reflected by mirrors, after which they are recombined and the interference patterns measured. ®

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