For a couple of years, gravitational waves are the central topic of numerous discussions. What do the physicists find so interesting on them is a combination of four factors, two of them very big and two very small:
1. Usually, gravity is a very weak force. You might find this slightly counter-intuitive since we feel its presence at every moment of our lives, but recall that a small electric charge of a balloon can make your hair stand – even though the gravity of the entire planet tells them otherwise.
2. In contrast to it, a black hole merger is an extremely energetic event. Two black holes, usually weighing like tens of suns, merge into a new black hole – which is lighter than the sum of two. The difference is turned into a colossal amount of energy and radiated in form of gravitational waves.
3. Fortunately, this happens very far away – usually around a billion of light years. It took the signal around one-tenth of the age of the Universe to reach us!
4. This mitigates the effect of gravitation waves by many orders of magnitude – so much that it is nearly impossible to notice them. In the result, they make the 4 km long arms of the LIGO and Virgo detectors periodically shorter and longer by a fraction of a nucleus size. Only the genius design makes the detection possible.
The detected signal is not just a simple beep, it has a rich structure which allows us to extract valuable information about the cataclysmic event.
It was a long journey, that began with the Einstein’s prediction back in 1916. The construction of the LIGO experiment began in 1994, but the first run between the years 2002-2010 lead to no success.
It was only shortly after starting the improved run in 2015 when the first detection exhilarated the team of LIGO/Virgo collaboration. Three of the most dominant figures: Barry C. Barish, Kip S. Thorne and Rainer Weiss were today awarded the Nobel prize (for decisive contributions to the LIGO detector and the observation of gravitational waves).
This prize does not conclude the story of gravitational waves though. There have been 4 detections officialy announced, all of them originating from a black hole merger. However, there is a gossip that this August gravitational waves from colliding neutron stars have been observed. A neutron star is nearly as extreme as a black hole, but not completely – light can still escape it. This means that might not have only captured the gravitational signal, but also its optic counterpart.
We are all eagerly anticipating what the near future will bring.
Dr. Samuel Kovacik – School of Theoretical Physics, DIAS