For the third time, the Laser Interferometer Gravitational-wave Observatory (LIGO) has detected the elusive gravitational waves, ripples in space-time resulting from the merging of two large stellar-mass black holes.
Designated GW170104, the phenomenon was observed on January 4, 2017, during an observing run that began on November 30 of last year and will continue through this summer.
An international scientific collaboration project, LIGO consists of two detectors, one in Hansford, Washington, and the other in Livingston, Louisiana. Funded by the National Science Foundation (NSF), the detectors are jointly run by Caltech and MIT.
After undergoing major upgrades via a program called Advanced LIGO, LIGO made its first detection of gravitational waves in September 2015 and its second three months later.
In all three cases, the gravitational waves came from the tremendous energy produced by two merging black holes. Such collisions generate more power than the light radiated by all the universe’s stars and galaxies at any given time.
The black holes that generated the spacetime ripples detected on January 4 had masses approximately 49 times that of our Sun. This puts them into an intermediate category between the 62-solar mass colliding black holes that resulted in the first detection and the 21-solar mass black holes that generated the second detection.
At a distance of approximately three billion light years, the most recent observation is the furthest seen to date. The previous two occurred at distances of 1.3 and 1.4 billion light years.
“We have further confirmation of the existence of stellar-mass black holes that are larger than 20 solar masses–these are objects we didn’t know existed before LIGO detected them,” said David Shoemaker of MIT, spokesman for the international group of scientists conducting the research, known as the LIGO Scientific Collaboration (LSC).
According to LIGO data, the spins of the two black holes that produced the January 4 detection were not aligned with one another.
Pairs of black holes spin around each other while also spinning on their individual axes. If they spin in the same direction that the pair is moving, the spins are considered aligned with one another.
Black holes with aligned spins likely originated as binary stars. Because the spins of binary stars are aligned with one another, they remain aligned even after both explode as supernovae, leaving black holes as remnants.
If the spins of two black holes are not aligned, they likely did not originate in a binary star system but came together within a crowded star cluster.
The sensitivity of LIGO’s detectors will be enhanced in another upgrade before its next observing run, scheduled for late 2018.
A paper on this latest detection has been published in the journal Physical Review Letters.