Science

Gravitational waves detected from more colliding black holes

The ground-breaking detection of gravitational waves, ripples in space and time postulated by Albert Einstein 100 years ago, that was announced in February was no fluke. Scientists said on Wednesday that they have spotted them for a second time.

2nd detection confirms that pairs of black holes are relatively common

This image depicts two black holes just moments before they collided and merged with each other, releasing energy in the form of gravitational waves. The newly detected waves were from black holes 14 and 8 times the mass of the sun that merged to form a new black hole 21 times the mass of the sun. ( S. Ossokine, A. Buonanno, T. Dietrich, R. Haas/Max Planck Institute for Gravitational Physics)

The ground-breaking detection of gravitational waves, ripples in space and time postulated by Albert Einstein 100 years ago, that was announced in February was no fluke. Scientists said on Wednesday that they have spotted them for a second time.

The researchers said they detected gravitational waves that washed over Earth after two distant black holes spiralled toward each other and merged into a single, larger abyss 1.4 billion years ago. That long-ago violent collision set off 
reverberations through spacetime, a fusion of the concepts of time and three-dimensional space.

These gravitational waves were observed by twin observatories in the United States late on Dec. 25, 2015 (early 
on Dec. 26 GMT). The detectors are located in Livingston, Louisiana, and Hanford, Washington.

The first detection of gravitational waves was made in September and announced on Feb. 11. It created a scientific sensation and was a benchmark in physics and astronomy, transforming a quirky implication of Einstein's 1916 theory of gravity into the realm of observational astronomy.

The waves detected in September and December both were triggered by the merger of black holes, which are regions so dense with matter that not even photons of light can escape the gravitational sinkholes they produce in space.

Upgraded sensitivity

The merging black holes that set space ringing in December were much smaller than the first pair, demonstrating the 
sensitivity of the recently upgraded Laser Interferometer Gravitational-wave Observatory, or LIGO, facilities.

U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO) has two detectors - one in Hanford, Washington, and the other in Livingston, Louisiana (above). (LIGO)

"We are starting to get a glimpse of the kind of new astrophysical information that can only come from gravitational-wave detectors," said Massachusetts Institute of Technology researcher David Shoemaker.

The black holes that triggered the newly detected gravitational waves were eight and 14 times more massive than 
the sun, respectively, before merging into a single, spinning black hole about 21 times more massive than the sun. The 
equivalent of one sun's worth of mass was transformed into gravitational energy.

The Louisiana site detected the waves first and the Washington state detector picked up the signal 1.1 milliseconds 
later. Scientists can use the timing difference to calculate a rough idea of where the black holes merger occurred.

Scientists say the second detection confirms that pairs of black holes are relatively common.

"Now that we are able to detect gravitational waves, they are going to be a phenomenal source of new information about our galaxy and an entirely new channel for discoveries about the universe," Pennsylvania State University astrophysicist Chad Hanna said.

The research, presented at the American Astronomical Society meeting in San Diego, will be published in the journal Physical Review Letters

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