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http://www.abc.net.au/news/2016-02-12/first-direct-evidence-of-gravitational-waves-detected/7140750

Einstein’s gravitational waves directly observed for the first time by LIGO scientists

Updated about 2 hours ago

Tiny ripples in the fabric of space-time known as gravitational waves first proposed by Albert Einstein 100 years ago have been directly observed for the first time, an international team of scientists has announced.

After months of speculation, the scientists from the Advanced LIGO project confirmed they had detected gravitational waves caused by two black holes merging just over a billion years ago.

LIGO executive director David Reitze confirmed to a press conference.

“We have detected gravitational waves, we did it.”

“It took us months of careful checking, rechecking, analysis.

“This is not just about the detection of gravitational waves … what’s really exciting is what comes next.

“I think we’re opening a window on the universe.”

“Like Galileo first pointing his telescope upward, this new view of the sky will deepen our understanding of the cosmos, and lead to unexpected discoveries,” France Cordova, director of the US National Science Foundation, which funded the work, said.

The team’s findings have been published in the journal Physical Review Letters.

Gravitational waves are ripples in space-time caused by the movement of objects with large amounts of gravity.

In 1915, Einstein predicted that gravitational waves would be produced in extremely violent events such as collisions between black holes or neutron stars.  But they had never been directly observed until now.

LIGO — which stands for Laser Interferometer Gravitational wave Observatory — uses a laser split into two separate beams which are sent down a pair of 4-kilometre-long perpendicular pipes.

The beams are reflected back by mirrors and cancel each other out unless a gravitational wave causes the detector to contract and stretch putting the beams out of sync.

On September 14 last year, scientists working at LIGO observatories 3000 kilometres apart in Livingston, Louisiana and Hanford Washington simultaneously detected vibrations from two rapidly spinning black holes — one about 29 times the mass of the Sun and the other about 36 times the Sun’s mass — as they spiralled together and merged into a single black hole about 1.3 billion years ago.

The black holes gave out a burst of gravitational waves that travelled through the universe at the speed of light, causing everything in their path to vibrate back and forth.

Signal ‘fits perfectly to gravitational waveforms’

Professor David Blair, director of the Australian International Gravitational Research Centre at the University of Western Australia is one of 56 Australian scientists who are part of the 1000-strong advanced-LIGO team.

He has spent decades working on perfecting the technology that made the discovery possible by the Advanced LIGO project.

“The signal at first seemed too good to be true and for many months mundane explanations were sought,” Professor Blair told RN’s Science Show.

But, he said, the waveforms of black holes are very specific and after extensive analysis all alternative explanations were ruled out.

“The incoming signals fitted perfectly to gravitational waveforms calculated by supercomputers,” he said.

Rumours about the Advanced-LIGO detection first surfaced late last year.

However, doubt remained as three senior engineers at LIGO can send a false or synthetic signal designed to mimic a gravitational wave through the observatory’s systems in order to test the science team.

In March 2014, a separate project called the BICEP2 collaboration claimed they had detected gravitational waves imprinted in the cosmic background microwave radiation — the left over heat from the Big Bang.  This was later found to be artefacts caused by foreground dust in the Milky Way Galaxy.

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