WASHINGTON, the U.S. and European scientists are teaming up to study one of the universe’s most elusive secrets — mysterious “gravity waves” that result when enormous objects collide in space.
What they learn could shed new light on an old concept, that collisions between galaxies or stars create waves of gravity just as explosions produce bursts of light.
The idea of gravity waves dates to 1916 when Albert Einstein developed his theory of general relativity about the forces in the universe. Scientists now hope to prove Einstein right by assembling a trio of spacecraft to record the first direct evidence of gravity waves.
If all goes well, the spacecraft should be able to see “systems of stars in very weird situations,” said Alan Bunner, who heads NASA’s office studying the structure and evolution of the universe.
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The Laser Interferometer Space Antenna (LISA) consists of three spacecraft flying 3.1 million miles (5 million kilometres) apart in the shape of an equilateral triangle as shown below.
Proposed for launch in 2009 aboard a single Delta 2 rocket, the $500 million Laser Interferometer Space Antenna (LISA) was the first space mission to search for gravity waves. The cost and construction of the three spacecraft will be split between NASA and the European Space Agency.
“It’s a mission that combines both fundamental physics and unique observations of astrophysics,” Bunner said.
LISAs five-year task is to study milestone events in the evolution of the universe, such as gigantic explosions and collisions. Researchers hope to be able to see as far back as 300,000 years after the Big Bang – the theoretical beginning of the universe.
“Everything we do as people is all about understanding the world around us and coming to grips with it,” said Lee Finn, a mission scientist at Pennsylvania State University. “This [mission] is another part of that enterprise.”
Gravity waves are thought to be ripples in the fabric of space and time that are produced by violent cosmic events, such as colliding galaxies or exploding stars. The waves radiate outward from such collisions at the speed of light, about 186,000 miles (299,300 kilometers) per second, and spread out indefinitely like ripples on a pond.
Scientists say that any accelerating object is capable of creating gravity waves — even something as slow as a speeding bullet. Therefore, our own Milky Way Galaxy contains gravity waves, although the waves are too subtle to detect.
LISA will be able to detect some of the faintest gravity waves because its three spacecraft would be positioned far apart from each other. From that vantage point, even slight wave motions should be evident to the probes.
Of course, if a collision of two stars happened in our own galaxy, Finn said, “we would see it with absolutely no problem at all.”
No one yet has actually seen or measured gravity waves although two scientists, Joseph Taylor and Russel Hulse, were able to indirectly detect their influence by observing a pair of burned-out stars in orbit around each other. The men won the 1993 Nobel Prize in Physics for their discovery.
LISA won’t be the only scientific facility sniffing out these strange phenomena.
While LISA is working in space to look for large, low-frequency gravity waves produced by massive colliding objects, a separate set of Earth-based detectors will be hunting a different type of gravity wave from the ground.
The Laser Interferometer Gravitational Wave Observatory (LIGO), built by a team of scientists from the California Institute of Technology and the Massachusetts Institute of Technology, will look for smaller gravity waves produced by pairs of stars and exploding objects.
Ligo mission for Gravity Waves
LIGO, a $300 million project funded by the National Science Foundation, is composed of two scientific labs located 2,000 miles (3,220 kilometers) apart in Livingston, Louisiana and Hanford, Washington. Both are far enough from cities to avoid most seismic or artificially caused vibrations.
But the LIGO detectors are still vulnerable to earthquakes, said Bill Hiscock, a project scientist at Montana State University.
“LIGO is subject to seismic noise, which grows dramatically in strength at [the lower] frequencies,” he said. “So there’s no hope of going to lower frequencies without going into space.”
The LIGO mission became operational in 2002. Eventually, scientists hope to build a new set of detectors that will be 10 times more sensitive and can survey a volume of space 1,000 times greater than those now available.
The LISA mission is actually three spacecraft that orbit the sun in a triangle formation about 28 million miles (45 million kilometers) from Earth. Each is positioned about 3 million miles (5 million kilometers) from the other.
The three are designed to detect gravity waves by measuring subtle changes in the spacecrafts’ position. Aboard are instruments sensitive enough to notice positional changes as small as one-fiftieth the width of a human hair.
LISA’s mission will fulfill a long-held dream of astronomers. “There has been a strong interest in moving gravity-wave detection to space for many years,” said Bunner.
So will Einstein’s theories hold true with the first firm detection of gravity waves?
“I frankly think that Einstein will be vindicated,” Finn said. “But that’s more of a religious belief; well have to wait and see.”
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1. Gravity!: The Quest for Gravitational Waves
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2. Gravitational Waves: How Einstein’s spacetime ripples reveal the secrets of the universe
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