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Gravitational Waves – A Crash Course

With the recent Nobel prize announcements and the ongoing Nobel Week in Stockholm, gravitational waves are back in the public spotlight. The 2017 Nobel Laureates for Physics this year are Kip Thorne, Rainer Weiss, and Barry Barish, “for decisive contributions to the LIGO detector and the observation of gravitational waves”. But what are gravitational waves? If you are asking yourself the same question, here is a crash course on gravitational waves.

What are gravitational waves?

Imagine space-time as being a mesh, much like a fishing net. When you place a heavy object such as a cannonball on the mesh, the mesh deforms under the weight of the object. Just like this, heavy objects deform space-time. When there is another, a lighter object placed on the mesh next to a heavier object, the lighter object’s movement is determined by the deformation caused by the heavier object. A ping-pong ball placed near the cannonball on the mesh would naturally move towards the dent created by the cannonball. However, if two heavy objects are placed on the mesh close to each other, they both affect each other’s movement. This leads to the apparition of ripples on the mesh; similar to ripples you would see appear when you drop something in still water. This would be the analogue of gravitational waves. Gravitational waves are ripples in space-time caused by two massive objects orbiting around each other and accelerating through space. An example of such massive objects may be a binary system of neutron stars (two neutron stars orbiting each other) or a black hole collision.

Detection of gravitational waves

Gravitational waves were predicted by Einstein’s Theory of General Relativity, and they have finally been directly observed thanks to the LIGO facility. Before this, their existence was only indirectly predicted due to certain behaviors of pulsars. Early in 2016, it was announced that LIGO had detected gravitational waves originating from a black hole merger i.e. when two black holes that are orbiting each other collide and merge. LIGO has gone on to detect more gravitational waves, stemming from different phenomena, such as a neutron star merger. You can read more about this recent discovery here, as well as how the LIGO detector actually works.

Impact on Astrophysics

This detection of gravitational waves opens a new window to how we can observe astronomical phenomena. So far, the only detection method was electromagnetic radiation and, thanks to LIGO’s discovery, we will be able to detect gravitational interactions from now on as well. Apart from that, there are other missions to detect more gravitational waves that will be launched, such as the LISA mission, which is a collaboration between NASA and ESA. Read more about it on NASA’s website. All in all, last year was an amazing year for astrophysics, and scientists are looking forward to studying the implications of this discovery and make progress.

Edited by Briana Fannin