AAS Post #2: Listening to the Universe

Contributed by
Jan 9, 2006

'I just attended a press conference for LIGO, the Laser Interferometer Gravitational Wave Observatory. This is a new way of observing the Universe, and it depends on a very odd prediction by Einstein.

Basically, what Uncle Al said was that space was not just, well, space, but actually a thing, a framework in which matter and energy exist. As such, it could be affected by matter, bent, distorted, like a tightly stretched sheet can be bent by placing a heavy weight on it.

But he made another astonishing prediction: if two massive objects were to collide, they would send out ripples, or waves, through space. These ripples bend the fabric of space, something like the ripples on a pond surface when a rock is dropped into it. In the case of Einstein, these are called gravitational waves.

When two black holes or superdense neutron stars collide, they can send out these ripples (in reality, the movement of anything generates gravitational waves, but the more sudden the movement and the more massive the objects, the sharper and easier to detect the waves are).

LIGO was built to listen to these waves. When a wave passes through space, it distorts objects within it. For your typical black hole collision way off in the distant Universe, this distortion is smaller than the size of a proton, so you'd never notice it in your daily life. But the engineers at LIGO have been struggling for years to fine tune their machine so that they can actually see this tiny ripple. The setup is a bit complicated, but basically they use a laser beam to measure the distance between two mirrors.

Last November, they finally got the detectors sensitive enough to hear astronomical sources. They can measure a ripple so small that if the mirror move by 10-18 meters -- 1/1000th the size of a proton! -- they can detect it. This means that if two neutron stars collide, and they're less than about 40 million light years away (basically, our local galactic neighborhood), they'll catch it.

This may seem all pretty weird and esoteric, but what this means is that LIGO may be opening a door on the Universe that was previously shut. If it works-- and it could make its first astronomical detection any time now -- then bigger projects are waiting down the line. More sensitive detectors would increase the range of LIGO, and NASA, along with the European Space Agency, are planning a space-based version called LISA, which would be able to hear two neutron stars colliding anywhere in the Universe.

These are still in the future. In fact, the first real detection from LIGO is sometime in the future, but probably not too much longer. I've been reading about LIGO for many years, and it's exciting to see it's online and ready to start its life as a research instrument.'

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