In 1916, Albert Einstein predicted the existence of ripples in the very fabric of space-time, though he lacked the technology to test his theory. These gravitational waves have been extremely difficult to detect – until now.
Researchers for the Laser Interferometer Gravitational-Wave Observatory (LIGO) recently announced that they had finally detected such waves, proving Einstein’s hypothesis to be true a full century later.
The discovery will likely change the way we do astronomy forever, and scientists are excited.
What are gravitational waves and what causes them?
Einstein’s reimagined gravity in his Theory of Relativity. He hypothesized that it was not merely a force pulling objects toward one another.
Space can be thought of like a gigantic, rubbery sheet. This sheet can be bent by the movement of literally anything with mass – you can distort space just by jumping up and down.
The more mass an object has, the greater the distortion it causes. For example, the sun is a very massive object, and it produces a large amount of distortion in a ring shape around it.
Smaller objects, like the planets in our solar system, cannot move straight through this field of distortion. Instead, they end up getting pulled around the sun in elliptical orbits. This bending of space is the effect that gravity has on objects.
How to detect gravitational waves
Because gravity is such a weak force, detectable ripples can only be produced by very massive objects moving through space at incredible speeds.
Using pre-existing knowledge of relativity, scientists can predict what gravitational waves should look like when emanating from objects including black holes or neutron stars. The signal found by LIGO researchers matches one predicted for a black hole binary system consisting of a pair of black holes – 36 times and 29 times more massive than our sun, respectively – orbiting one another exponentially faster as they get closer together and finally merge into one giant black hole. All of this occurred 1.3 billion light-years away.
In order to detect a stretch or compression of space, scientists need a device that can measure the length of space itself. Normal rulers are useless for this – gravitational waves stretch objects the same way they stretch space.
Instead, LIGO researchers built a sort of ruler that uses the speed of light to measure distortion with the incredible precision needed to do so.
LIGO has two massive detectors separated by thousands of miles: one located in Livingston, La. and the other at the Hanford site in Washington.
Each detector consists of two perpendicular tunnels in the shape of an L, each four kilometers in length. If a gravitational wave passes by, the space inside of one tunnel will be stretched and the space inside of the other will be compressed.
Gravitational waves are just the beginning
The discovery of gravitational waves opens up the doors for scientists to do a new kind astronomy that doesn’t rely on the electromagnetic spectrum.
Until recently, what we can observe thanks to different types of radiation – such as visible light, infrared, and x-rays – is all that we have been able to see of the universe.
LIGO’s discovery made history in two respects – not only did we detect gravitational waves for the first time, but we also directly observed black holes for the first time. Black holes are invisible, detectable only by the movement of matter around them.
Black holes are still largely mysterious to astronomers. How they grow to such massive sizes is still up for debate. The discovery of gravitational waves has given us direct evidence of two black holes merging, which could help to eventually unravel the mysteries behind how black holes grow.
Reading gravitational waves offers us a completely new way to explore the cosmos, which will allow us to test current theories about how the universe works and will likely lead to more discoveries we never expected.
Featured Image: https://www.ligo.caltech.edu/news/ligo20160211
Guest post written by Megan Ray Nichols, who loves discussing the latest scientific discoveries with others on her blog, Schooled By Science. You can also follow her on twitter @nicholsrmegan