The LIGO observatory is finally back, now with double the sensitivity

LIGO is back for its fourth observation run

Gravitational waves, also known as ripples in space-time, are created by events such as black hole mergers, clashing neutron stars, and supernovae. They reverberate throughout the cosmos and can teach us a great deal about these cosmic events that play a great role in shaping the universe.

LIGO is composed of two detectors, one in Hanford, Washington, and the other in Livingston, Louisiana. Each one is made up of two concrete pipes connected at the base two to form a large L-shape. They extend perpendicular to each other for roughly 4 kilometers (2.5 miles).

Welcome to the fourth observing run! #O4IsHere

O4 will last 20 months, with @ego_virgo and @KAGRA_PR joining us in the run. We expect the detection rate will be roughly twice in our past observing run

More news linked from https://t.co/kHnyuP8I2I #ObservingRun4 pic.twitter.com/B9fhEG96r0

— LIGO (@LIGO) May 24, 2023

Inside these pipes, two powerful laser beams bounce off mirrors that extend the entire length of each arm. When a gravitational wave disturbs the laser, it allows the system to measure it with extreme precision.

Since 2015, LIGO has completed three observation runs. The first, four-month, run made history by making the first direct detection of gravitational waves in history. Each one has lasted longer than the last, with the third one going on for a total of 11 months. Now, the current run will last almost double that time.

LIGO upgrades will allow us to "learn more about black holes and neutron stars"

Unlike the previous runs, this one will also be enhanced by observations from both Virgo in Europe and KARGA in Japan. Virgo has observed alongside LIGO since the second run, but KARGA is new.

By the end of the third run in March 2020, researchers at LIGO and Virgo had detected about 90 gravitational waves from a black hole and neutron star mergers.

In an interview with The Conversation, LIGO team member Chad Hanna explained that the new quantum squeezing upgrade required 300 meters (1,000 feet) of the optical cavity. Hanna explained that the reduced noise, as well as improvements to the detection software, should now allow the team to detect much weaker gravitational waves.

"Thanks to the work of more than a thousand people around the world over the last few years, we'll get our deepest glimpse of the gravitational-wave universe yet," Jess McIver, the deputy spokesperson for the LIGO Scientific Collaboration (LSC) explained in the press statement.

"A greater reach means we will learn more about black holes and neutron stars, and increases the chances we will find something new," McIver continued. "We're very excited to see what's out there."