If you’ve been paying attention to the news this year, you may have heard about the discovery made by the Laser Interferometer Gravitational-Wave Observatory (LIGO). A “normal” astronomical observatory looks at light coming from distant objects- this one looks for expansions and contractions of physical space caused by gravitational waves. This phenomenon is explained in the theory proposed by Einstein, the General Theory of Relativity. This theory sounds scary, I know, but it states that space and time are interwoven into a “fabric”. From this, we can understand gravitational waves and how LIGO eventually detected them earlier this year.
Einstein’s theory, as stated before, says that space and time act as a fabric. This means that it can be pushed and pulled, squeezed and stretched, just like a piece of spandex. But instead of your hands pulling and squishing the fabric, objects with very large masses cause the deformation. This is why smaller objects orbit larger ones in systems in space; take the Earth and moon for example. This can be pictured with the Earth as a bowling ball sitting on a piece of stretchy fabric: the bowling ball causes a large dip in the fabric and if you were to place a marble, which represents the moon, into motion around the bowling ball, it would move in circles around the bowling ball. Planets orbiting stars work the same way!
Now, knowing that massive objects can bend space, two massive objects orbiting each other should cause gravitational waves- exactly what LIGO was looking for. Gravitational waves can be thought of as ripples in the spacetime fabric with distances in space being stretched and others being squished (see image below). This is measured by LIGO using several laser interferometers. Each device looks at a laser split into two beams of light and compares how the beams of light match up. If one of the distances the beams travel is expanded or contracted due to the gravitational waves changing space, the way the beams line up will not be the same and can be detected by the observatory! LIGO did exactly this in late 2016. Unfortunately, it was not able to be confirmed through a visual observatory since both objects in the orbiting pair were blackholes.
Image of gravitational ripples from LIGO simulation
In June of 2017 though, a detection of gravitational waves was able to be confirmed through observational astronomy as well. A pair of neutron stars (very dense stars that are late in their lives) were observed spiraling into each other and colliding and the resulting ripples of gravitational waves were detected by LIGO. Other gravitational observatories were able to confirm that the source of the gravitational waves was the neutron star collision. This is the first time an astronomical event of this scale was observed in both light and gravitation.
This detection along with the others made by LIGO mean big things for Einstein’s Theory of Relativity and astronomy in general. This evidence corroborates the predictions made by the theory and makes it that much stronger. Einstein’s theory of relativity has withstood any test put to it, making it even stronger. We also now have an entirely new “pair of glasses” that can be utilized in astronomy that will make our understanding of the universe that much better.
This article was written by Contributor Mikayla Cleaver ’19.