Discovering Gravitational Waves

Challenge

As an undergraduate, David Blair’s mentor at UWA challenged him to look out for the most difficult problems around. David chose gravitational waves and whilst it didn’t take the predicted year or two to discover, he was never deterred by critics. Sustained by optimism, 40 years later the dream was realised.

Professor Blair and his team started building a detector consisting of a huge bar of niobium at UWA in 1976 in the hope of detecting these waves. It operated with four others in the Northern Hemisphere from 1993 – 2000. They were the most sensitive detectors in the world. It was realised that a new type of detector could become much more sensitive. By then, the Laser Interferometer Gravitational-Wave Observatory (LIGO) had been designed in the Northern Hemisphere in the USA and these could make the next step in sensitivity.

In 2005, the team predicted the new LIGO laser detectors would be disrupted through light bouncing off sound waves. They commenced researching the phenomenon at UWA’s Australian International Gravitational Research Centre (AIGRC), Gingin. 10 years later the UWA group’s predictions were proved at the LIGO detectors. Carl Blair, a PhD student in Physics and David’s son, was sent to the LIGO Livingstone observatory, to help solve the problem.

For the last 40 years that I’ve been working on gravitational waves we’ve had people coming to us saying this is impossible, you’ll never detect gravitational waves. We’ve had to persist against this current of scepticism and these people who said it was impossible. We pursued the impossible and we succeeded.

Professor David Blair

Solution

On 14 September 2015, Carl was working at LIGO Livingstone. He finished working at 2.00am and left his post to an operator. Two hours later a dramatic signal appeared. It was morning in Germany and Marco Drago, a young physicist from the collaboration alerted the LIGO community. The signal seemed too good to be true and no one quite believed it. After months of effort everyone was convinced.

There were two black holes; one 36 times as massive as the sun, and the other 29 times as massive as the sun. Each spiraled together at incredible speed, initially around 50 times per second, then at 100 times per second until they finally merged into a single black hole, giving out a vast gravitational wave explosion; the biggest burst of energy in the universe ever observed by mankind. What is incredible was that the ripple of gravitational waves travelled for a billion years before it reached the solar system. By the time it reached us the ripple was less than the size of a proton!

The new black hole was 62 times as massive as the sun. A mass of three times the mass of the sun had been turned into pure gravitational waves in less than one tenth of a second.

LIGO has recognised the importance of their international collaborators in the discovery including the AIGRC’s role in controlling the instability of the LIGO laser, enabling the increase in power and sensitivity to bring these first signals.

The Australian International Gravitational Research Centre (AIGRC), Gingin was always planned to become a large scale observatory in the Southern Hemisphere to help triangulate the signals and pin point where the ‘sounds’ are coming from. When that happens, the improved sensitivity will enable to physicists to determine:

• How many black holes are out there in the universe?
• How much of the mass of the universe has already been lost into black holes?
• How fast is the universe expanding?

The research by Professor Blair and his team at UWA and AIGRC has been heavily funded by an Australian Research Council grant with further support from the University of Western Australia.

Impact Pathway

The technologies developed by the team are superbly sensitive and go way beyond equivalent technologies. They are adaptable to other industries and applications such as in searching for underground minerals and for airborne instrumentation. The team has just announced a new technology that they call Cat-flap resonators which they designed for improving gravitational wave detectors, but which are likely to have many other practical applications.

For the general public, the discovery provides us the opportunity to listen to the universe and understand the messages we hear. Professor Blair and his team are also exploring the musical properties of gravity waves and the opportunity to collaborate with musicians on new and different forms of music.

Professor Blair is passionate about teaching Einsteinian physics and alongside the Gravity Discovery Centre has been promoting its inclusion in the school curriculum. Their Einstein First program which can be taught in primary or secondary school places focus on the frontiers of physics rather than the history, as is traditionally taught.

So how does this discovery affect astronomers? Professor Blair recalled that astronomers would say “You guys (physicists) won’t be astronomers until you have detected gravity waves.” “Now that they have been detected astronomers really can’t stop talking about gravity waves.” Professor Blair said.

How would Einstein feel?

In 1916 Albert Einstein predicted the existence of gravitational waves. However in the 1930’s he wrote a paper claiming they did not exist. It was confirmed that Einstein’s theory predicted real waves but by this time Einstein had died. It was his healthy scepticism mixed up with his genius that earnt Einstein the respect of future physicists. 100 years after Einstein’s prediction, we can only imagine his astonishment and excitement at this discovery.

What does a gravitational wave sound like?

Professor Blair described walking through the bushland on his way over to our interview. He could hear chirping coming from within the woolly bushes. “It just sounds like gravity waves”, he described. Physicists expected the first sound to be long slow chirp, taking a minute or two to reach the final crescendo. In fact, the first sounds they detected was a very brief chirp . He believes that before long, we will be deluged with more and more sounds from the universe.