One of the most remarkable experiments in history – a pair of giant machines observing wave-waves, known as gravitational waves, in space-time, will wake up from a half-year nap on Monday. And it will be about 40% stronger than before.
This experiment is called the Laser Interferometer Gravitational Wave Observatory (LIGO). It consists of two huge, L-shaped detectors, which together have solved a 100-year-old puzzle by Albert Einstein.
In 1915 Einstein predicted the existence of waves in the tissue of space. He did not believe, however, that these gravitational waves would ever be discovered – they seemed too weak to catch in the midst of all the sounds and vibrations of the earth. For 1
Even when hundreds of scientists worked on LIGO from 2002 to 2015, they have "heard" no waves. This was despite the predictions that collisions of two black holes should produce gravitational waves at detectable levels. However, the 13-year slump ended in September 2015, when an upgraded "advanced" LIGO discovered its first gravitational waves: signals from the fusion of two black holes about 1.3 billion light-years away. The following December, the team discovered a second collision event. By 2017, three researchers who worked on the concept of LIGO received a Nobel Prize for physics.
Science has not been the same since then. LIGO's global research team today made eleven discoveries of severe collisions in space. However, gravitational-wave astronomy is still in its infancy, and the teams behind each observatory are constantly trying to improve the sensitivities of their machines.
Actually, LIGO wakes up after a series of hardware upgrades from his second big sleep. The scientific collaboration estimates that the devices are 40% more sensitive than in the previous run, which lasted from November 2016 to August 2017.
"We will certainly detect even more gravitational waves from the previously known sources," said Peter Fritschel, LIGO's chief investigator at MIT, in a press release. "We are also looking forward to new events, such as the fusion of a black hole and a neutron star."
This third run of the observatory is expected to take a full year.
How LIGO Works According to an animation created by researchers behind the experiment and how the improvements made by LIGO became even more sensitive.
How LIGO detects gravitational waves
] LIGO are actually two different but almost identical instruments that work together.
The two L-shaped detectors – each with 2.5-mile arms – are separated by nearly 1,900 miles. One is located in Hanford, Washington (where the Cold War nuclear weapons production took place) and the other in Livingston, Louisiana.
Together, the detectors searched for gravitational waves for years without luck, until 2015 when a new and improved "advanced" and improved LIGO system went online.
One of the notable collisions it has since observed called "GW170817" and announced in October 2017, came two neutron stars together. Astronomers who saw the signal alerted telescopes around the globe to bring the event to zero. The resulting multi-messenger observations indicated that the disaster spewed unimaginable quantities of silver, gold, platinum and other new elements of the periodic table into space.
Read more : Astronomers have discovered that gold worth 100 Earth or so has been forged in space – so much is worth it.
Each LIGO detector fires a laser beam and makes its observations split into two parts. One beam is sent down a 2.5-mile tube, the other one an identical but vertical tube.
The rays bounce off the mirrors and converge near the beam splitter.
The light waves return the same amount of time and align themselves so that they cancel each other out.
As a result, the light detecting part of the instrument does not see light.
But when a gravitational wave comes through, it shortens space-time – one tube gets longer and the other shorter. This rhythmic stretching and pinching distortion continues until the wave is over.
When this type of interference occurs, the two light waves are not the same length when they return, so they do not line up and neutralize each other. So the detector would take a few flashes of light.
A physicist who measures these brightness changes would measure and observe gravitational waves.
This setting is extremely sensitive. When a wave passes, the length of the arm after LIGO changes by less than 1/10 000 of the width of a subatomic proton particle.
This also means that a detector can be disturbed by the vibration of trucks driving on nearby roads, or even a light breeze.
That's why there are two LIGO instruments: if they detect a signal that occurs at exactly the same time, it is likely that a large gravitational wave will go through the Earth.
The events that cause these waves in space must be unimaginably strong. So far, LIGO has confirmed that black holes have been fused. When two black holes merge, the collision can immediately transform the mass of several suns into pure gravitational wave energy, which is why we can detect them on Earth more than a billion miles away.
Strogner laser beams, better mirrors and "squashed" light
Yet such events are relatively rare and their signatures are exceedingly weak.
The last upgrade of LIGO lasted 10 months in 2016 and increased its sensitivity by about 25%. The latest upgrade lasted six months and ends on April 1st. The sensitivity has been increased by 40%, in addition to the last upgrade of LIGO.
This increased sensitivity was intended to help scientists determine the location of neutron collisions, for example, up to 550 million light-years away, or about 190 million light-years away.
This jump is based on doubling the power of each LIGO laser. Each machine also received five out of eight mirrors and new hardware to capture and reduce stray light. It can now also "squeeze" photons of light (to resolve noisy data) using quantum physics.
"We had to break the fibers that hold the mirrors and carefully remove and replace the optics," said Calum Torrie, head of Caltech's LIGO mechanical-optical design department, in a press release. "It was an enormous technical task."
Vicky Kalogera, astrophysicist at Northwestern University and LIGO, previously told Business Insider that the experiment could ultimately detect 100 collisions a year – that is, using a third detector called Virgo, a new facility called KAGRA Japan, and other gravitational wave detectors.
"This has opened a new window to what we can see in the universe," said Imre Bartos, a physicist at Columbia University and LIGO, previously told Business Insider. "We can see that, now we can see gravitational waves, but we discover the really exciting things with these gravitational waves."
This is an updated version of a story published on November 30, 2016.