Gravitational wave detector LIGO is back online after a 3-year upgrade
By measuring gravitational waves, astronomers can look directly into the heart of some of these amazing phenomena in the universe.
A bird's-eye view of the Laser and Vacuum Instrumentation Area (LVEA) at the Laser Interferometer Gravitational-Wave Observatory (LIGO) Hanford Laboratory near Hanford, Washington, containing pre-stabilized lasers, beam splitters, input test masses, and other equipment. June 8, 2014 Photo by Caltech/MIT/LIGO Laboratory Posted on February 8, 2016 Coupled detectors, a system of two identical detectors, built to detect incredibly small vibrations from gravitational waves, Livingston, Louisiana, and Hanford, Washington. Scientists say that on February 11, 2016, they detected for the first time gravitational waves, motions in space and time hypothesized by physicist Albert Einstein centuries ago, opening a new window into the study of the universe. | Photo credit: Reuters
After a three-year hiatus, scientists in the United States have turned on detectors capable of measuring gravitational waves - tiny bursts of space that travel through the universe.
Like light waves, gravitational waves are almost completely blocked by galaxies, stars, gas, and dust. This means that by measuring gravitational waves, astronomers like me can look directly into the heart of some of these amazing phenomena in the universe.
Since 2020, the Laser Interferometric Gravitational-Wave Observatory — commonly known as LIGO — has been sitting dormant while it undergoes some exciting upgrades. These improvements will significantly increase LIGO's sensitivity and should allow the facility to look at more distant objects that produce small ripples in spacetime.
By identifying more events that produce gravitational waves, astronomers will have more opportunities to observe light produced by those same events. Observing an event through multiple channels of information, an approach called multi-messenger astrophysics, offers astronomers a rare and coveted opportunity to learn about physics beyond the scope of any laboratory experiment.
Ripples in space-time
According to Einstein's theory of general relativity, mass and energy distort the shape of space and time The curvature of spacetime determines how objects move relative to each other—what people experience as gravity.
Gravitational waves are created when massive objects like black holes or neutron stars collide with each other, causing sudden changes in space. The process of space warping and flashing sends ripples through the universe like waves across the pond. These waves travel in all directions from a disturbance, bending momentarily as they do so and slightly changing the distance between objects.
Although the astrophysical phenomena that cause gravitational waves involve some of the largest objects in the universe, the expansion and contraction of space is infinitesimally small. A single strong gravitational wave passing through the Milky Way can only change the diameter of the entire galaxy by three feet (one meter).
First Gravitational Wave Observation
Although predicted by Einstein in 1616, scientists of that era had little hope of measuring the tiny changes in distance postulated by the theory of gravitational waves.
Around 2000, scientists from Caltech, the Massachusetts Institute of Technology and other universities around the world finished building what is actually the most accurate ruler ever built - the LIGO Observatory.
LIGO consists of two separate observatories, one located in Hanford, Washington and the other in Livingston, Louisiana. Each observatory is shaped like a giant L, with two, 2.5-mile-long (four-kilometer-long) arms extending 90 degrees to each other from the center of the facility.
To measure gravitational waves, researchers shine a laser from the center of the facility to the base of the L, where the laser is split so that a beam travels up each arm, reflects off a mirror and returns to the base. If a gravitational wave passes through the arm while the laser is shining, the two beams will always return to the center at slightly different times. By measuring this difference, physicists can tell if a gravitational wave passed through the facility.
LIGO began operating in the early 2000s, but was not sensitive enough to detect gravitational waves. So, in 2010, the LIGO team temporarily shut down the facility to make upgrades to increase sensitivity. An upgraded version of LIGO began collecting data in 2015 and almost immediately detected gravitational waves produced by the merger of two black holes.
Since 2015, LIGO has completed three observing runs The first, Run O1, lasted about four months; the second, O2, about nine months; And the third, O3, ran 11 months before the COVID-19 pandemic closed facilities Starting with Run O2, LIGO has been observing together with an Italian observatory called Virgo.
Between each run, scientists improved the detector's physical components and data analysis methods. Until the end of the O3 run in March 2020, researchers from the LIGO and Virgo collaborations will be able to detect a mixture of black holes and neutron stars.
