Gravitational waves have been observed for the fourth time bringing new insight into the fabric of the universe. The discovery has an important “first” too. It was the first time gravitational waves were detected by three observatories instead of two.
Having three detectors reduced the area of sky where the signal could originate from by about 10 times. It also gave scientists a new way to test relativity.
The gravitational waves were produced by a 30.5 solar masses black hole merging with a 25 solar masses one. This merger happened about 1.8 billion light-years from Earth and the resultant black hole has a mass equivalent to 53 times our Sun. Therefore energy released by the cosmic collision is about 3 times the mass of the Sun.
The merger is the second largest ever detected and provides more confirmation that medium-size black holes, bigger than those produced in supernovae, are common in the universe. But gravitational waves help us understand more than just black holes. The detection provided the opportunity to test more predictions of Einstein’s general relativity.
For example, are gravitational waves polarized? Polarization describes how space-time is stretched in three dimensions by the propagation of gravitational waves. The researchers looked at two extreme scenarios: the polarization predicted by Einstein versus the polarization forbidden in general relativity. So far, the data agree with Einstein, but further analysis might provide a more nuanced picture.
This sort of analysis wasn't possible using the two LIGO detectors, one located in Hanford, Washington and the other in Livingstone, Louisiana. The Virgo detector, however, is located in Italy and has a different orientation with respect to the Earth, allowing for this new test of general relativity.
“The Virgo collaboration and the LIGO Scientific Collaboration have been working together for many years to analyze the data and extract precious information from the observed signals. A three-detector network opens up a new potential, allowing further fundamental tests of theoretical predictions,” said Frédérique Marion, a senior scientist who worked on the analysis, in a statement.
A lot of people were hoping that the detectors had caught gravitational waves from neutron stars and that the team was able to catch a bright flash of light from the collision. This wasn’t the case. But the three detectors are better at triangulating so if this chance arises they will probably be ready.
The next run of observations is planned to start in the fall of 2018. The three detectors will now undergo some tweaking that will hopefully improve their sensitivity by a factor of two.
