Black hole detector to get major upgrade

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The LIGO Louisiana lab that detected gravitational waves is in line for an upgrade

The UK and US governments have announced a £25m upgrade to the machines that detected gravitational waves three and a half years ago.

The improved instruments will be able to detect collisions of black holes nearly twice as far away.

By 2024 they will be able to observe in unprecedented detail more than three such cataclysmic events each day.

Details were announced at the American Association for the Advancement of Science meeting in Washington.

Prof Sheila Rowan of Glasgow University, who will be among those leading the project, said the upgrade will help us understand more about black holes, gravity and neutron stars.

“We have already learned so much from the ten black hole and one neutron star collisions we have observed,” she said.

“We are still at the very start of what (the instrument) can deliver for us across a number of areas of science.”

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Ligo labs fire lasers through long tunnels, trying to sense ripples in the fabric of space-time

What are Gravitational Waves?

Gravitational waves are ripples that are sent across the Universe when the gravity in a certain point in space suddenly changes, caused by the collision of two black holes, for example. The process is similar to the ripples caused by a pebble thrown into a pond, but in the case of gravitational waves, space and everything in it is the pond.

Like water ripples, everything in the path of the waves: stars, planets, houses, even people, get fractionally taller and slimmer and then shorter and fatter, as they pass through. But the distortions are tiny – much less than the width of an atom.

Einstein predicted the existence of such waves in 1916, but is reported to have said that they were too small to ever be detected. But he was proved both right and wrong 100 years later, when an international team discovered them using a pair of 4km-long L-shaped machines called Advanced Ligo.

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Media captionPallab Ghosh explains the sound of the gravitational wave and a computer visualisation

How does Advanced Ligo work?

Extremely well, say the researchers involved. In fact, the machine detected gravitational waves soon after it was turned on.

The Ligo team went on to detect nine more black hole collisions and one collision of two dead stars called neutron stars in the next two years. This suggested that we live in a violent Universe, where such cataclysmic events are the norm.

The L-shaped instrument is essentially made up of two highly accurate rulers at 90 degrees to each other. Each arm has a laser beam which bounces off a mirror at the other end. The time it takes to return is a measure of the length of each arm.

When a gravitational wave from space hits, the L-shape is first stretched and then squashed by a tiny amount for a fraction of a second, but it’s enough of a change to be detected.

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What will the upgrade be called?

Unimaginatively, it will be called Advanced Ligo Plus, but that does mean it can be given the acronym of A+, which the marketing people are sure to like.

Much of the “plussing” will be carried out by a UK team led by researchers at the Institute for Gravitational Research at Glasgow University, which has the expertise to build the high precision instruments needed to measure the miniscule distortions gravitational waves create.

Researchers there will be increasing the sensitivity in four ways. First, they will have better, shinier mirrors; second, the mirrors will have an improved coating, which reduces the wobbling of molecules on the surface; third, the suspension system on which the mirrors are hung will be made even more stable, and, lastly, light is known to be fuzzy at the quantum level. With the help of a team in Australia, researchers are sharpening it up by squeezing the fuzziness.

What will A+ study?

By being able to detect more black hole collisions, researchers will be able to learn more about them, especially at their edges, where the laws of physics start to break down.

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BBC News

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Researchers at Glasgow University are developing special coatings to sharpen up the focus of the mirrors used in the gravity wave detectors

As well as an increase in quantity, scientists will be able to observe collisions in much greater resolution – in ultra-high definition compared to what they can currently detect. Harder to detect are the collisions of dead stars, called neutron stars.

These are fascinating because all the burning gas has collapsed into itself to form a super dense material. One teaspoon of the material weighs 10 million tonnes.

Physicists want to know what this material is like. And it’s thought that neutron stars produce gold and platinum and other heavy metals when they collide.

So far the current instrument has detected just one. A+ will be able to detect 13 each month.

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Media captionFive reasons why gravitational waves matter

And, perhaps most intriguingly, it might be able to resolve a mystery about the speed at which the Universe is expanding. Ground-based telescopes looking at far away supernovas come up with a different answer to the Planck space telescope, which is looking at the cosmic radiation left over from the Big Bang.

A+ will measure the expansion by looking at the behaviour of gravitational waves. It will either find that measurements from the ground telescopes or Planck is wrong or, hopefully, that something really weird is going on.

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