The Laser Interferometer Gravitational-Wave Observatory (LIGO) has detected gravitational waves produced by two merging black holes that were three billion light-years distant. This is the farthest distance from which LIGO has detected gravitational waves produced by an event like this. The detected gravitational wave appears to be undiminished, which provides further proof that gravitational waves travel at the speed of light.
Before merging, one black hole measured 31 times the mass of our sun and the other measured 19 times our sun’s mass. When they merged, the resulting, larger black hole became 49 time the mass of our sun. The “missing” one percent was converted into the gravitational wave, following Einstein’s famous equation, E = MC2.
Observing the gravitational waves from merging black holes may help solve some mysteries about how mid-sized black holes form. Small black holes usually form when stars that are massive enough to collapse into a black hole die. However, until LIGO, scientists didn’t know much about the formation of mid-sized black holes that aren’t big enough to provide a centerpoint for spiral galaxies like ours.
Chad Hanna, a LIGO scientist from Pennsylvania State University, mentioned that they had only been working with a few weeks’ worth of data when the discovery was announced. “We plan to run until August. … We might still detect more events,” she said.
LIGO has two detectors. One is located in Hanford, Washington, and the other is located in Livingston, Louisiana. The two detectors picked up the gravitational wave only a fraction of a second apart. Only extreme events such as supernovas, neutron stars and the merging of two black holes are capable of producing gravitational waves that LIGO can detect. This isn’t a weakness in the instrument. Rather, gravity is the weakest of the four fundamental forces and that makes gravitational waves difficult to detect.
Further upgrades to the instrument may make it more sensitive. Scientists also hope to use LIGO to detect the collision of binary neutron stars. These collisions are believed to have created heavy elements like gold. If a collision is detected, an alert will be sent out to the scientific community so that interested scientists can point their telescopes at that spot in the sky and observe the event.
The detection of gravitational waves like the ones produced by the merger of black holes and collisions between neutron stars may improve our understanding of gravity and its related particle, the graviton. It may also help physicists refine theories that have withstood experimental testing for more than 100 years. LIGO may help with the refining of these theories by detecting more events like the merging of these two black holes.