A Seven Billion-Year-Old Signal from Merging Black Holes Reaches Earth

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A Seven Billion-Year-Old Signal from Merging Black Holes Reaches Earth

This cosmic signal rattles Earth after 7 billion years

The BBC reported a fascinating scientific story about signals created from merging black holes traveling for 7 billion years to be picked up on Earth. Detected by laser technology, specifically three super-sensitive gravitational wave-detection systems, the signals were picked up in the United States and Italy in May 2019.

"It's astounding, really," said Prof Nelson Christensen from the Côte d'Azur Observatory in France. "This signal propagated for seven billion years. So this event happened 'just before halftime' for the Universe, and now it's mechanically moved our detectors here on Earth," he explained to BBC News.

And that, believes Prof Martin Hendry, from Glasgow University, UK, has implications for how the Universe evolved. "We're talking here about a hierarchy of mergers, a possible pathway to make bigger and bigger black holes," he said. "So, who knows? This 142-solar-mass black hole may have gone on to have merged with other very massive black holes - as part of a build-up process that goes all the way to those supermassive black holes we think are at the heart of galaxies."

This data will help astronomers and astrophysicists better understand the gravitational waves generated by black holes. A black hole is a region of space where matter has collapsed in on itself. They're called black holes because the gravitational pull is so strong that nothing, not even light, can escape. Often created during the explosive demise of large stars, they can be gigantic, even up to billions of times the mass of our own sun. Though hard to spot, they're detected by the gravitational pull they exert on objects around them.

“If someone does a cannonball dive on the other side of the pool, it takes a while for the waves to reach you,” said Dr. Joshua N. Winn, Professor of Astrophysical Sciences at Princeton University. “Likewise, when black holes crash into each other, there’s a delay before the resulting distortions in space reach us. But, while a water wave might travel a few meters per second, gravitational waves travel at 300 million meters per second—the same speed as light.”

“One way to visualize the effect is to imagine a series of circular rings, arranged to make a cylinder,” he said. “Send in a gravitational wave along the axis of the cylinder [and] each ring gets alternately stretched one way, then the other. The result is a traveling pattern of distortions.”

The Laser Interferometric Gravitational-Wave Observatory (LIGO) helped detect the waves using using the wave nature of photons to sense these incredibly small distortions. Dr. Joshua N. Winn, one of the team, described the technology.

“At the end of each tunnel is a highly reflective mirror, which bounces the light back to the beam splitter, and from there the light either goes back toward the laser or bounces to a photo detector,” he said. “If the two laser beams arrive at the detector in phase—that is, if each crest arriving from the west is met by a crest arriving from the north—then the beams interfere constructively.

“If, on the other hand, the two optical paths differ by half a wavelength, then the waves interfere destructively.”

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