Gravitational waves detected at last as black holes collide

Jubilant scientists have made one of their most important discoveries ever by detecting gravitational waves from two colliding black holes, they announced today.

Black holes colliding
An artist’s impression of a pair of black holes closing in for a merger. Image credit: SXS

The colossal collision occurred 1.3 billion light-years away from Earth. But it produced ripples across space and time like the ripples in a pond. And one washed across us last year, causing a tiny distortion in reality.

Two separate and incredibly sensitive detectors that are part of a UK-backed experiment measured a gravitational wave from the event. They have never been observed before but were predicted by Albert Einstein, 100 years ago in 1916.

The discovery, much anticipated in recent days, also marks the first time that two black holes have been observed to collide.

Einstein, famous for his Theory of General Relativity that describes how the Universe works, said that space and time are part of one fabric holding it all together, called a continuum.

He said that objects like planets and stars distort the shape of the spacetime continuum, like weights that cause a trampoline’s surface to flex. The more massive the object, the greater the distortion it causes.

But the effect is almost imperceptible, and Einstein did not believe we would ever be able to spot them. Scientists had to build the most precise measuring machine ever and then wait for a cataclysmic event somewhere in the Universe to identify the ripples it would cause.

LIGO Hanford
One of the LIGO observatories, the L-shaped facility at Hanford, Washington. Image credit: Caltech/MIT/LIGO Lab

The gravitational waves were produced in the final fraction of a second of the merger of the two black holes, and with the power of all the billions of galaxies of stars combined.

The detection was made on September 14 by twin detectors called LIGO—short for Laser Interferometer Gravitational-wave Observatory—in Livingston, Louisiana, and Hanford, Washington. They were specially built to look for gravitational waves.

The tiny ripple in space and time would usually be imperceptible against the interfering effects around us, which is why it was vital for it to be confirmed by two stations. Each comprises two tubes in an L-shape, with each tube two and a half miles long. The detection was made by shining lasers through a vacuum in the tubes and onto a mirrors.

By constantly measuring the precise distance of the mirrors, and with the laser beams travelling at the fixed speed of light, a shift in the distance of the mirrors can reveal there has been a warp in the spacetime continuum.

The distortion revealed today was so tiny that it was equal to one thousandth the width of an atomic particle.

Astronomers had previously observed effects in the orbits of a pair of massive stars which demonstrated the existence of gravitational waves. But the waves themselves had never been detected. Scientists say it opens ups a whole new window in observing the Universe and discovering how it formed.

Building LIGO to detect gravitational waves was the brainchild of Professor Rainer Weiss, of Massachusetts Institute of Technology, and Professor Kip Thorne and Professor Ronald Drever, both with Caltech.

Weiss said: “The description of this observation is beautifully described in the Einstein theory of general relativity formulated 100 years ago and comprises the first test of the theory in strong gravitation. It would have been wonderful to watch Einstein’s face had we been able to tell him.”

Thorne commented: “With this discovery, we humans are embarking on a marvelous new quest: the quest to explore the warped side of the universe—objects and phenomena that are made from warped spacetime. Colliding black holes and gravitational waves are our first beautiful examples.”

UK scientists played leading roles in designing the LIGO experiments and making the discovery. Professor Sheila Rowan, Director of the University of Glasgow’s Institute for Gravitational Research, said: “This is a monumental leap forward for physics and astrophysics—taking Einstein’s predictions and turning them into an entirely new way to sense some of the most fascinating objects in our Universe.”

Professor Alberto Vecchio, of the University of Birmingham, helped develop the techniques to tell what event caused gravitational waves recorded. He said: “This observation is truly incredible science and marks three milestones for physics—the direct detection of gravitational waves, the first observation of a binary black hole, and the most convincing evidence to-date that Nature’s black holes are the objects predicted by Einstein’s theory.”

Paul Sutherland

Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.
Paul Sutherland

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Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.

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