The LIGO collaboration won the Nobel Prize in 2017 for the detection of ripples in spacetime (gravitation waves) from two black holes merging about one billion light-years away. This measurement has been elusive since Einstein predicted it a century ago as the experiment must be sensitive to distances one part in 1021; that’s one atomic nucleus per mile! Recently, this collaboration observed the merger of two neutron stars. Neutron stars are the extremely dense, and their merger has a completely different gravitational wave profile than the previous black holes. Another collaboration called ‘Virgo’ was able to detect the signal. Due to the three points of detection, scientists were able to make a much tighter estimate on where in the sky the merger happened.
There are a lot of exciting implications from this experiment, even for particle physics. The merger came with a burst of light that was detected simultaneously with the gravitational waves. This suggests that gravity propagates at the speed of light, something physicists theorized but lacked strong evidence. This observation will then tighten the bound on how massive a graviton, the particle representation of gravity, can be. Only massless particles can travel at the ‘speed of light,’ the relativistic limit on how fast anything can travel in the universe.
This observation has confirmed and supported several existing theories, and future detections certainly will teach us more about physics at the astronomical and infinitesimal scale.
Managing Correspondent: Cari Cesarotti
More: https://physics.aps.org/articles/v10/114