The New-Age Telescope

Conquering a feat long thought to be impossible, the scientists and engineers of the Laser Interferometer Gravitational-Wave Observatory (LIGO) have a lot to be proud of. Their recent detection of gravitational waves for the first time ever has opened up many doors for astrophysics as a whole. Because the effects the waves create are so minimal, a very precise and well-designed piece of equipment was needed to be built, and that's exactly what the people at LIGO accomplished. By exploiting certain properties of the waves they were able to sense when these waves were passing through their apparatus.

For my post today I will be discussing:

• The main characteristic of gravitational waves that scientists use to detect them
• How the Laser Interferometer Gravitational-Wave Observatory functions

 

Behavior of Gravitational Waves 

A ring of particles influenced by a gravitational wave

Like mentioned previously, Gravitational waves have the ability to pass through matter unchanged. This means that the waves are same when they reach us as they are when they left the source of the waves. However, even though the wave is not altered by the matter, the matter is in fact affected by the wave. When a gravitational wave passes through a plane, that plane is periodically stretched and squeezed. This process is illustrated in the graphic to the right. It is this behavior that allows us to analyze and detect them.

Laser Interferometer Gravitational-Waves Observer

 

So how would one exploit this property? Well in order to detect when these waves pass through you would need to measure when the distance between two points in space has been stretched. Sounds fairly simple right? Well it's actually quite difficult. Intuitively, when you want to measure the distance between two objects you could just use some sort of ruler. The problem with applying this idea is that even though the distance between the points is stretched, so is the "ruler", and to an observer nothing will seem to have changed. To measure this type of change we must use something that remains constant no matter the outside influences: the speed of light in a vacuum. With a system of lasers and mirrors, LIGO was able to use the constant speed of light to their benefit.

The LIGO observatory is made up of two vacuum-sealed tunnels, each four kilometers long and positioned so they are perpendicular with one another. A laser is split down each tunnel, and reflected back and forth many times between mirrors until recombining at a light detector. The apparatus is set up such that when the tunnels are at their normal unstretched length, the waves will recombine and cancel each other out. However when a gravitational wave passes through, the tunnels are stretched and compressed and the distance each beam of light travels will be different. This change in distance will make the beams no longer cancel each other out when recombining.

One of the biggest problems with these machines is isolating the system so that no outside sources might create false readings. Because the system is making such precise measurements, some of the most light vibrations from the outside world can cause these problems. Vibrations were initially to much of a problem to make accurate readings at LIGO, but with improvements made to their equipment in 2010 it is no longer an issue. As a fail-safe to ensure that the detector didn't make a false detection, two different observatories were built in locations far away from one another. Having two different locations also helps us to trace where the wave originated from.

If you're interested in learning more, Brian Greene joined the Late Show with Stephen Colbert to do an entertaining, hands-on experiment for how these observatories function.

Thanks to the amazing pieces of equipment at LIGO we were able to detect gravitational waves for the first time ever. However, just because we have come up with with the first functional design does not mean the innovation stops here. Similar to how we have improved on the telescope since it's invention, scientists are continuing to look for better ways of designing gravitational wave detectors. What the future holds for these detectors is unknown but certainly exciting.

Sources:

Schilling, Govert. "Gravitational Waves Hit Prime Time." Sky & Telescope (2015): 26-31. Ebsco Academic Premier. Web. 27 Apr. 2016.

Harry, Gregory M. "Advanced LIGO: The next Generation of Gravitational Wave Detectors." Classical and Quantum Gravity 27.8 (2010): n. pag. Web. 27 Apr. 2016. 

Daw, Ed. A ring of particles influenced by gravitational wave. Digital image. PHYS ORG. N.p., 11 Feb. 2016. Web. 27 Apr. 2016. <http://phys.org/news/2016-02-ligo.html>. 

"Gravitational Waves Hit The Late Show." YouTube. YouTube, 25 Feb. 2016. Web. 27 Apr. 2016. <https://www.youtube.com/watch?v=ajZojAwfEbs>.