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THE RELATIVISTIC UNIVERSE

In Einstein's universe, mass is converted into energy in the cores of stars, enabling them to shine, while matter curves space, and time flows faster or slower depending on relative motion or gravity. Einstein's General Theory of Relativity has largely stood the test of time; its manifestations are much evident in the observable universe. Indeed, current models of how the cosmos began and evolved are largely founded upon Einstein's theory.

Present models acknowledge that in "the big picture," gravity reigns supreme and alone will decide whether the universe keeps expanding or falls back on itself in a "Big Crunch." So it's understandable that some physicists remain unsettled that a key prediction of Einstein's General Theory, namely gravitational radiation, remains unverified nearly 80 years later.

Then there are black holes. It wasn't until after Einstein's death that black holes were conceived, though the spacetime singularities they are contain were anticipated early on by some physicists, beginning with Karl Schwarzschild. Most relativity researchers now believe that General Relativity is not only consistent with black holes but demands that they exist under certain conditions. Prove that black holes populate the co smos, and you've pretty much confirmed an important component of General Relativity. Also, if black holes are for real, under certain conditions they could prove to be powerful sources of gravitational waves, which are also po stulated by General Relativity. However, other cosmic phenomena could generate these ripples in spacetime.

When all is said and done, the jury is still out on both counts for lack of conclusive evidence. Nevertheless, over the past decade, impressive advances in both intrumentation and computation are at last making it possible to put General Relativity throug h its ultimate trial. Many scientists are confident that it will emerge not merely unscathed but triumphant. But first, though, tomorrow's gravitational wave astronomers need to catch their quarry. For this they need a list of prime suspects whose "finger prints" can be matched to the gravitational waveforms predicted by theory.

According to General Relativity, the key qualities of strong sources of gravitational waves are that they be non-spherical, dynamic (i.e. change their behavior with time), and possess large amounts of mass moving at high velocities. So prime suspects should exhibit one or more of the following characteristics.

Spinning
Embedding diagram of spinning object.

A large, non-symmetric object disturbs the fabric of spacetime when it spins, causing gravitational waves to propagate outward.

Mass Transfer
Illustration
of mass transfer in a binary star system.

When two large objects orbit each other, matter may be transferred from the less dense to the denser object. The more massive, compact object "accretes" matter from its neighbor due to its greater gravitational pull. Mass transfer may result in gravitatio nal radiation.

Collapse
Illustration of collapse of a large object.

When the inward gravitational pull of an object is no longer resisted by outward pressure, it collapses catastrophically, converting some of its mass into gravitational energy and radiating gravitational waves. However, once again this can only occur if t he collapse is non-spherical.

Explosion
Illustration of stellar explosion

Cosmic explosions such as supernovae, which may follow the collapse of a massive star, trigger shock waves in the surrounding space. As long as the explosion and resulting shockwave are non-spherical, they will trigger gravitational waves.

Collision
Illuistration of cosmic collision.

Colliding or coalescing objects will emit gravitational waves. The more massive they are, the greater the wave energy.

Why not check out the "line up" of the suspects?

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Copyright 1995, The Board of Trustees of the University of Illinois


NCSA. Last modified 11/8/95.