It is approaching midnight on September 13th, 2015 at the LIGO facility at the Hanford Reservation. Operators have recently finished the upgrades to LIGO, which has now been dubbed Advanced LIGO, in the hunt for Gravitational Waves. Corey Gray, a lead operator at LIGO who has been with the project since the beginning, helps the operator in control room prepare for an Engineering Test run of Advanced LIGO before heading home to go to sleep. At 2:51am PST or 5:51am EST on the morning of September 14th, while Corey is sleeping, it happens. The LIGO detectors in Livingston, Louisiana and Hanford, Washington detect gravitational waves 7 milliseconds apart.
Immediately after detecting the gravitational waves, the computer system automatically sends notification emails to scientists all over the world, which is standard operating procedures, to signal an event has occurred. The scientists who receive these emails call both LIGO detectors to make sure everything is okay; however, the operators in both locations are clueless. Looking at the data later, it is clear. Gravitational Waves have been detected. At that moment, the world had changed, the final prediction of Einstein’s Theory of Relativity has been proven correct.
It turns out that the signal that was heard during this Engineering Run of Advanced LIGO was the real deal. LIGO at Hanford heard the bigger signal, while the Livingston LIGO heard the signal first. The computers do not analyze the data until the machines are turned off, at which time, the data is sent to supercomputers to process. That would explain why at the time of the detection, the operators at both locations did not realize what they had found. After analyzing, countless double checking the data, and calculating the numbers, the data was clear, LIGO had indeed calculated a Gravitational Wave created by the most powerful force in the universe, 2 black holes colliding. The mass of the 1st black hole was 29 solar masses, with the 2nd black hole having a mass of 36 solar masses, which were both traveling at nearly the speed of light at the time of the merger. The fact that this event was confirmed is amazing considering that the Livingston LIGO was only running for part of the day and in order to confirm a discovery, both LIGO detectors had been running. Therefore, if the team in Hanford had not been running at the time, then the LIGO team would NOT have been able to officially publish the results.
Ever since this discovery of Gravitational Waves, other countries have been scrambling to build their own versions of LIGO to assist in the search. India which will build and turn on a version of LIGO in about 5-7 years time, Italy has a version of LIGO which is being used this run of Advanced LIGO in the spring of 2016. Germany is planning to build a version of LIGO with 500 meter arms. Japan is going to build a version of LIGO inside mine of mountain with 3km arms, which will go online in 2019.
The two instances of LIGO in Hanford and Livingston are separated by 3000 miles, which takes light 10 milliseconds to travel that distance. Therefore, for LIGO to confirm and detect gravitational events, both detectors will have to spot the event within 10 milliseconds or else the event was not a gravitational wave.
LIGO detects Gravitational Waves
It is crucial that noise is minimized as the detectors are extremely sensitive as gravitational waves show up as waves and changes on the scale of 1 x 10 to the -19th power, which is on the scale of protons. Therefore, events like Earthquakes, North Korean Nuclear Explosions, or even semi trucks running over potholes can and have the ability to cause issues with the data. When there is an Earthquake, LIGO will shut down until the Earth stops ringing if the magnitude is 5 or above. (The Earth will ring for a few days after an Earthquake of that magnitude)
This can best be shown by a great story that the tour guide gave, which was that the control room operators of LIGO started noticing spikes in their data during the same time every day in the morning. LIGO will send people to investigate every little disturbance, which was found out to be the employees driving over the LIGO employee parking lot speed bump. The speed bumps were removed so that it wouldn’t disturb the data that the detect was picking up.
Gravitational Waves are so important because it not only confirms what Einstein had predicted, but it also provides an entirely new way to perform astronomy and new ways to study the universe.
The tour was awesome! Hanford LIGO has 2 tours to the public per month, which always occur on the second Saturday of the month at 1:30 pm and on the fourth Friday of the month at 3:00 pm as per their site. The Livingston LIGO tour occurs every 3rd Saturday of the month. The tour in Hanford starts with an operator providing a discussion and slide deck presentation, which was done by the wonderful Mr. Corey Grey. The story above is actually what happened according to what he mentioned. The tour also continues with a walk around the facility to the Control Room and an overview of the concrete tunnel which covers the tunnel. The tour guide said that there was much debate over whether the concrete covering should even be built as the concrete was expensive. However, it has turned out to be a great idea, because there was a driver who wasn’t paying attention and crashed into the concrete slabs. If the concrete was not built, the driver would have crashed right into the experiment itself. That would have been a total disaster if that had happened, as it took 40 day to create the vacuum seal inside the LIGO tubes. At the time that LIGO was built and the vacuum tubes were created, the vacuum tubes were the longest and largest vacuum structure in the world. The Large Hadron Collider in Switzerland, run by CERN, has since taken the top spot as the worlds largest vacuum chamber.
The locations of the initial LIGO experiment started with the 2 LIGO sites in the US, which were determined to be in Hanford and Livingston because of budget and political reasons. Livingston is not in an ideal location because the Livingston version of LIGO is built on softer soil and there are issues with logging and hunting in the area. Livingston is able to constantly run at 20 megaparsecs, whereas the Hanford LIGO can run consistently at a range of 80 megaparsecs. This difference of range of sensitivity, means that the lower sensitivity means fewer findings. Increasing the sensitivity means more findings and more discoveries. The LIGO tubes are 35cm across, and the longer the tubes are, the more sensitive the detectors can be.
There are 2 ways to increase sensitivity, which is either making the arms longer, or to increase the watts of the laser. Being on the Hanford nuclear site, there is enough room to build, with the only limit being as far as the eye can see. However, due to the cost and having to start including the curvature of the earth in the calculations, the LIGO team will start increasing sensitivity by increasing the wattage from 20 watts to 50, and then finally to 200 watts of initial power and increase the number of bounces that the light takes before being recombined. It is worth noting that at the time of discovery, LIGO was not operating at design specifications, nor was the equipment as sensitive as it should have been. It is amazing considering that when fully up to specifications, LIGO will be able to make some additional and numerous findings. With the development of similar observatories in other countries will help scientists triangulate findings and discover astronomical phenomena like Supernova and Pulsars, which would be verified and viewed with the appropriate telescopic equipment.
It was surprising how much data is generated during the running of all of the machinery. LIGO generates a total of 1 petabyte of data per year, which is either dumped or used, because the cost and effort to upkeep the data would not be worth the effort. For example, CERN at the LHC creates 26 petabytes of data a year and uses physical tapes to store the data.
Note, this article is intentionally not technical as this can be easily understood and appreciated by anybody. The original running had a total of 0 Gravitational Wave findings. This had led to the scientists upgrading the technology to become more sensitive, which would lead to the discovery. For a summary of the future of gravitational wave detectors such as this one, check out our article.