“Don’t tell your friends, I think we might have found those waves,” MSU physicist Neil Cornish told his son James in September 2015. He was referring to gravitational waves, a phenomenon predicted by Einstein’s theory of general relativity in 1915 but never determined empirically. On Thursday, Feb. 11, Cornish announced to a packed Procrastinator Theatre that the international team of researchers that he works with succeeded in detecting gravitational waves for the first time on Sep. 14, 2015.
The gravitational wave detected was the result of two black holes merging to form a single black hole 1.3 billion years ago. The event created a ripple in spacetime, which continued outward until it reached the team’s Laser Interferometer Gravitational-wave Observatory detectors in Hanford, Washington and Livingston, Louisiana. While the two detectors are located at opposite sides of the country, they detected the wave only seven milliseconds apart. According to Cornish, the detectors are “the most sensitive measuring devices ever built by man” and are able to detect a wave that only changed the distance between the Earth and the sun by the width of an atom.
Both black holes were exceptionally large; while all previously measured black holes had a mass 5-15 times that of the sun, these two were measured to have 36 and 29 solar masses. After merging, the resulting black hole was 62 times the mass of the sun, indicating that the energy from three solar masses was emitted in the form of gravitational waves. This means the event was the most energetic ever observed in the universe. In comparison, gamma ray bursts, the previously most energetic events observed, are at least 1,000 times less energetic. The mass of the black holes was determined by entering collected data into a computer model and altering 15 parameters until one combination provided a good fit. “We’ve figured out the language of black holes. We can decode the message that black holes deliver,” Cornish said. Previously, the mass of black holes could not be determined by observing it directly but only by analyzing the mass’ effect on surrounding objects.
The observed situation was also unique in that it was a binary system of black holes, where two black holes came together rather than just one black hole colliding with a star. “In our wildest dreams, we never thought that the first one we found would be so spectacular,” Cornish said.
One of MSU’s roles in the research was creating an analysis method of the gravitational wave. Cornish and his team created the BayesWave algorithm and used it to extract the coherent part of the wave. This analysis is unique in that it can isolate a gravitational wave signal without making any assumptions based on a model. The detected waves matched those created by a model which made assumptions based on Einstein’s theory by 94 percent.
There are currently three gravitational wave detectors being used for the project: two in the US and one in Germany. The device in Germany was not operational during the event. During the next two decades, three more detectors will be added, which Cornish anticipates will allow the observation of more gravitational waves and give scientists the ability to determine a more precise location where the observed cosmic events took place. “This is the beginning of gravitational wave astronomy, not the end,” he said.