Detecting gravity waves

A revolution in astronomy might be just around the corner — if Einstein’s description of gravity turns out to be correct. Albert Einstein predicted that when massive objects — say, two black holes — interact, they produce so-called “gravity waves” that ripple out through the universe.

And some astronomical observations are best explained by the existence of gravity waves. But no one has managed to detect gravity waves directly. Richard Matzner specializes in relativity theory at the University of Texas at Austin.

Richard Matzner: It’s sort of a two-edged sword — it’s hard to detect gravitational radiation because it doesn’t interact with the detectors very strongly. And you need significantly strong gravitational fields in the first place to produce it. But once it’s produced, it just zips through things — it transparently passes through the sun for instance — and then interacts just strongly enough with our detectors that we think that we’ll be able to do astronomy with it.

Matzner’s project is called LIGO — the Laser Interferometry Gravity Wave Observatory. It consists of two large detectors in Washington State and Louisiana. The detectors contain mirrors separated by several kilometers. If gravity waves pass through, the distance between the mirrors should change slightly.

Scientists are already using LIGO to take some test data. Matzner hopes it’ll prove Einstein right — that gravity waves do exist.

No one has directly detected gravity waves. But Joseph Taylor was awarded the Nobel Prize for measuring the spin-down rate of binary pulsars, and showing that this rate was consistent with the rate at which the binary system was losing energy in the form of gravitational radiation.

Most scientists working in the field believe LIGO will find these gravity waves and help to answer many fundamental questions in astrophysics.

Stars that collapse and explode as supernovas should also produce gravity waves. But scientists are at a complete loss to explain how a dying star explodes with the force that it does when it goes supernova. So LIGO might help.

LIGO consists of two large detectors in Washington State and Louisiana — that are linked together by computer networks. The detectors — called “laser interferometers” — contain tiny mirrors that move when gravity waves pass through them. Lasers detect the motion. Each of the two detectors is housed in an L-shaped tube with each leg running 4 kilometers — 2.5 miles — long.

Matzner is looking forward to the first detection of gravity waves, and looking ahead to the next decade as he helps to plan a “next generation” gravity wave detector in space that may be able to pick up signals from the first million years after the big bang. According to Matzner, “One of the things about gravitational radiation is that it doesn’t interact strongly with things it’s passing through. So the universe is more transparent to gravitational waves than it is to electromagnetic waves. So we have the ability to look even farther back in time — that is even further away, therefore farther back in time — using gravitational radiation.”

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