Hot on the heels of the first detection of a gravitational wave, a second has been recorded by scientists at the twin Laser Interferometer Gravitational-Wave Observatory (LIGO).
Gravitational waves or ripples, are a form of radiation — ripples in space-time that travel at the speed of light. They were first proposed by Albert Einstein in his theory of general relativity in 1916. But because these ripples are so subtle, and precise instrumentation is needed to record them, they had gone undetected until observed on Sept. 14, 2015.
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Gravitational waves are created by cataclysmic events in our universe, such as two merging black holes. In the case of the first detection, two black holes about 30 times the mass of our own sun, moving at the speed of light, merged taking 1.3 billion years to arrive at the LIGO detectors.
The LIGO detectors are incredibly sensitive: they can measure a ripple in space-time down to as little as 1/1,000 the diameter of a proton.
The detection was a breakthrough in cosmology. These waves help cosmologists understand the nature of gravity that can’t otherwise be observed.
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The second gravitational wave — named GW151226 — was observed on Dec. 26, 2015.
Scientists believe that the waves were created as two black holes — one 14 times the mass of the sun, the other eight times the mass — merged about 1.4 billion years ago. Specifically, the waves were detected during the final 27 orbits of the black holes. Out of that merger came a larger black hole about 21 times the mass of our sun.
“It is very significant that these black holes were much less massive than those observed in the first detection,” says Gabriela González, LIGO Scientific Collaboration (LSC) spokesperson and professor of physics and astronomy at Louisiana State University. “Because of their lighter masses compared to the first detection, they spent more time — about one second — in the sensitive band of the detectors. It is a promising start to mapping the populations of black holes in our universe.”
The first direct detection of a gravitational wave rocked the scientific community when it was announced in February. In 1993, Russel A. Hulse and Joseph H. Taylor Jr. won the Nobel Prize in Physics for indirect detection.