BATON ROUGE – Scientists who study black holes and their impact on the universe are making strides in their research at Louisiana's Laser Interferometer Gravitational-Wave Observatory (LIGO).

After several months of thorough analysis, the LIGO Scientific Collaboration and the Virgo Collaboration have released an updated catalog of gravitational wave detections.

The catalog contains 39 new signals from black-hole or neutron-star collisions detected between April 1-Oct. 1, 2019, which more than triples the number of confirmed detections. The new set includes some of the most interesting systems seen so far, and will lead to additional research related to the new findings. 

The sharp increase in the number of detections was made possible by significant improvements to the instruments used. Improvements included increased laser power, better mirrors and, perhaps most significantly the use of quantum squeezing technology.

According to a July 2020 article in Physics World, when physicists make measurements on a laser signal, uncertainties arise from quantum fluctuations in the numbers of photons detected and the times at which the photons arrive at the detector. The relationship between this pair of uncertainties is described by the uncertainty principle, which dictates that a decrease in uncertainty in photon number must be accompanied by an increase in uncertainty in timing and vice versa. Reducing the uncertainty of one measurement at the expense of increasing the other can be advantageous in some experiments — and is called quantum squeezing.

So, use of quantum squeezing tech and other innovations resulted in a roughly 60 percent improvement in the range to which signals can be detected. The detectors were also able to operate without interruption more often than in the past, with an improved duty cycle of about 75 percent, versus about 60 percent previously.

“As an instrument scientist, your focus is on making the instrument better all the time. So even when the instrument is observing, we’re looking at the data coming out of it to see if there is noise somewhere we don’t expect there to be,” said LSU Department of Physics & Astronomy PhD candidate Corey Austin. 

The new signals pave the way for members of the scientific community to implement research projects that will lead to a better understanding of the populations of black holes and neutron stars.

LIGO says that by analyzing the entire population of binary black hole mergers simultaneously, astrophysical information extracted is maximized. It is inferred that the distribution of black hole masses does not follow a simple power-law distribution. Measuring the deviations from this power law will improve the ability to learn about the formation of these black holes, either as the result of stellar deaths or previous collisions.

Considering the entire population together also helps make stronger measurements of difficult-to-measure properties such as black hole spin. Some merging black holes have spins which are misaligned with their orbital angular momentum. This will help probe the regimes in which these binaries formed.

LIGO says the many signals in the updated catalog will put Einstein’s theory of gravity to the test in more and better ways than before. This was done by comparing the data against predictions from the theory and constraining possible deviations. The results from multiple signals were combined using new statistical methods to obtain the tightest constraints so far on the properties of gravity in the strong, highly-dynamical regime of black hole mergers. With the new catalog, LIGO and Virgo were also able to directly study the properties of the remnant objects produced during the mergers: by measuring the vibrations of these objects, and by ruling out potential “echoes” after the main signals, LIGO and Virgo confirmed that the remnants behaved as expected from black holes in Einstein’s theory.

“We still need to know more about the universe. Just think of how we discovered new elements, which are now common knowledge,” said LSU Post-doctoral Researcher Guillermo Valdes, who works at LIGO Livingston as part of the team, led by LSU Boyd Professor Gabriela González, constantly improving the sensitivity of the instrument.

The results reported in the new catalog at ligo.org correspond to only the first six months of LIGO and Virgo’s third observing run. Results from the remaining five months are currently being analyzed.

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