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Listening to the cosmic buzz of 100,000 black hole mergers

It has only been a few years since astronomers made the first innovative detection of gravitational waves, which are waves in space-time that propagate outward from especially violent cosmic events, such as the fusion of black holes. And since then, a total of six gravitational wave events have been confirmed. But despite the novelty of this new method to investigate the universe, some astronomers are already getting anxious.

Specifically, two researchers have moved away from detecting individual gravitational wave events, and now they are focusing on a larger picture. In an article published in the journal Physical Review X the researchers describe a new and highly sensitive technique to detect the faint hum of the more than 100,000 gravitational wave events that are believed to occur in the universe each year. . Although the new technique will not allow them to focus on individual events of gravitational waves (such as LIGO and Virgo), it will give them the information they need to put restrictions on both the distribution and the rate of fusion of black holes throughout the universe.

According to the document, "Approximately every 2-10 minutes, a pair of stellar mass black holes merge somewhere in the Universe." A small fraction of these mergers are detected as gravitational wave events that can be resolved individually by Advanced detectors like LIGO and Virgo. "However, the rest of the waves mix, creating a weak cosmic buzz called gravitational wave background.

"Measuring the background of the gravitational wave will allow us to study populations of black holes at great distances," said co-author Eric Thrane, an astrophysicist at the ARC Center of Excellence for Gravitational Wave Discovery (OzGrav) and Monash University. in a press release. "Someday, the technique will allow us to see the gravitational waves of the Big Bang, hidden behind the gravitational waves of black holes and neutron stars."

The new method for detecting the long-desired hum of countless gravitational waves depends on checking seas of noisy data and unraveling any signal from previously hidden black holes. But to do this, researchers need an extremely powerful supercomputer.

Fortunately, that's exactly what they have in the form of the new $ 4 million supercomputer known as OzStar. According to a statement from Matthew Bailes, director of OzGrav, "in a second, the machine can perform 10,000 calculations for each of the 100 billion stars in our own galaxy." In addition, he said: "It is 125,000 times more powerful than the first supercomputer I built in the institution in 1998." By combining their innovative technique with such a powerful device, the researchers estimate that the new method to detect gravitational waves will be 1,000 times more sensitive. than other detectors.

However, at this point, the researchers have only tested their new technique on data generated through computer simulations of weak black hole signals. But within those simulated data, they found unequivocal evidence of black hole collisions that arise from background noise.

Although the technique still needs to be tested with real data, co-author Rory Smith, an astronomer at OzGrav and Monash University, is confident that the method will make a true detection. According to Smith, recent advances in high-speed data analysis will allow astronomers to finally detect "what people have been looking for for decades": the weak but persistent buzz of the gravitational wave background.

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