Gravitational waves detected

Scientists have detected gravitational waves, ripples in space and time predicted by Albert Einstein a century ago, in one of the biggest discoveries in physics for decades.

The discovery was announced on 11 February by the team working on LIGO, a pair of giant detectors in the United States. Scientists from the University of Birmingham played a major part.

What are gravitational waves?

Einstein's general theory of relativity, published in 1915, describes gravity as a curving of space and time by massive objects. He predicted that violent events, such as the collision of massive stars, would send out ripples in the fabric of space-time, travelling at the speed of light.

But the waves are so faint that Einstein doubted they could ever be detected.

The discovery

The signal was picked up on 14 September last year by both LIGO detectors, in Louisiana and Washington state. It was produced by two black holes, around 29 and 36 times the mass of the Sun, spiralling into each other and merging about 1.3 billion years ago.

In a fraction of a second, the collision gave off more power than all the stars in the observable universe put together, in the form of gravitational waves.

How LIGO works

Each LIGO detector has two arms, four kilometres long, arranged in an L-shape. Laser beams bounce back and forth along the arms. When a gravitational wave passes, it stretches one arm and squeezes the other by a tiny amount, less than a thousandth of the width of a proton.

Birmingham's role

Scientists at the University of Birmingham helped develop the techniques used to identify the signal and work out the properties of the black holes. Researchers from Cardiff, Glasgow and other British universities were also involved, and Britain provided key technology for the detectors.

The Birmingham team is led by Professor Alberto Vecchio, and the university has been involved in gravitational wave research for many years.

A new window

Scientists say the discovery opens a new way of studying the universe. Until now, astronomy has relied almost entirely on light and other forms of radiation. Gravitational waves could reveal events that are invisible to telescopes.

It is also the first direct evidence that pairs of black holes exist and can merge.

Many physicists believe the discovery will be recognised with a Nobel Prize.