Upgraded LIGO hears new tones in the gravitational wave song
For the first time, scientists have managed to pick up higher harmonics accompanying the cosmic song that rings out through the universe. The LIGO and Virgo gravitational wave detectors have been listening to this song for years, and after a round of upgrades they’ve extended their range, revealing new details about the events that cause them.
When massive objects collide in space, they send waves rippling through the very fabric of spacetime. These gravitational waves were a prediction of Einstein’s Theory of General Relativity, but we weren’t able to pick them up until 2015. Since then, signals have come in so regularly that they’ve almost become mundane – to reiterate, measuring distortions in reality itself is no longer news.
That is, unless there’s something special about a given event. And in this case, observers have detected higher frequency waves than ever before.
Last year the LIGO and Virgo observatories began their third observation run, called O3, after a lengthy upgrade process to make them more sensitive. And less than two weeks into O3, they picked up a strange new signal designated GW190412. This detection featured higher harmonics, which are waves with frequencies two or three times higher than the fundamental frequency usually heard.
From this, the researchers were able to infer that the source of the signal was a collision between two black holes with very different masses. One has eight times the mass of the Sun, while the other has 30. In all other black hole collisions detected to date, the mass of the two objects is roughly the same.
“For the very first time we have ‘heard’ in GW190412 the unmistakable gravitational-wave hum of a higher harmonic, similar to overtones of musical instruments,” says Frank Ohme, a researcher on the study. “In systems with unequal masses like GW190412 – our first observation of this type – these overtones in the gravitational-wave signal are much louder than in our usual observations. This is why we couldn’t hear them before, but in GW190412, we finally can.”
The researchers say that the unequal masses are clear in the way the gravitational waves ripple through the cosmos, and this can help scientists measure certain properties more accurately, such as how far away the objects are, what angle we’re looking at them from, and how they’re spinning.
The team is now looking at 54 other candidate detections that were spotted over the past year, for further clues.
The research is available on the pre-print server ArXiv, and an animation of the black hole collision can be seen in the video below.
Source: Max Planck