Gravitational Waves

Imagine someone cannonballs into a pool, what happens? Ripples are created and run through the entire pool. Now instead of a pool think about spacetime, and instead of someone canon-balling, think about two major stars colliding. Those ripples are gravitational waves. First discovered in Albert Einstein's general theory of relativity, gravitational waves are the disruptions in space-time that two accelerating objects create. These disruptions take place in the form of waves of space-time that disseminate in all directions away from the source. Gravitational waves travel at the speed of light and have many different causes, including black holes, supernovas, and colliding stars.

The first proof of gravitational waves was found in 1974 when two astronomers reported a change in the radio emissions from two stars and that the stars were getting closer and closer to each other at the rate of general relativity, proving Einstein’s theory. In 2015, scientists detected gravitational waves themselves from a collision of two black holes for the first time using an instrument called LIGO (Laser Interferometer Gravitational-Wave Observatory). While the collision of two black holes that LIGO detected happened 1.3 billion years ago, the ripples didn’t make it to Earth until 2015. LIGOs detect the squeezing and stretching that gravitational waves create. Each LIGO machine has two arms that are around 4 kilometers long, and a gravitational wave will cause the length of the arms to change marginally. The LIGO machine uses lasers, mirrors, and other tiny instruments to detect these tiny changes. While gravitational waves are initially very strong and dangerous, by the time they reach Earth they are much smaller. This is because the waves get smaller and smaller the farther away they are from the source, just as the ripples made by the cannonball decrease by the time they reach the edge of the pool. In fact, by the time the gravitational waves hit Earth from that collision of two black holes 1.3 billion light years away, the amplitude generated was 10,000 times smaller than the nucleus of an atom. While gravitational waves don’t have a large effect on Earth, they give scientists a new way to explore the universe. Scientists are able to learn more about black hole mergers, supernovas, and the birth of the universe all through gravitational waves. 

References

What are gravitational waves?. Caltech. (n.d.). https://www.ligo.caltech.edu/page/what-are-gw 

NASA. (2020, June 4). What is a gravitational wave?. NASA https://spaceplace.nasa.gov/gravitational-waves/en/