Photo of exploding star gives scientists evidence of a `negative gravity' force

Research confirms one of Einstein's ideas about energy in space


A photograph of a distant exploding star has given astronomers the first direct evidence that a mysterious "negative gravity" force swept through and still pervades the universe, according to NASA scientists.

The exploding star, the most distant ever observed, was photographed by luck in 1997.

But scientists say subsequent detective work involving the relative intensity of its light confirms one of Einstein's conjectures about the universe: that all of space is now bubbling with an invisible form of energy that creates a mutual repulsion between objects normally attracted to each other by gravity.

Einstein thought the force, which he called the cosmological constant, was so strange that he later repudiated it.

But the idea gained theoretical support in 1998 with findings suggesting that the expansion of the universe is accelerating, and that the accelerating force or negative gravity - the manifestation of the cosmological constant - overtook the force of gravity some time in the past few billion years.

Explanations ruled out

The new findings confirm that crucial prediction. And they rule out a number of competing explanations.

Because the total amount of this negative gravity in any given volume should be minuscule, its effects would go unfelt in everyday life.

But over vast distances involving huge volumes of space the antigravity effect would be powerful enough to push whole galaxies and clusters of galaxies apart from one another.

Exploding stars, or supernovas, like the one that turned up unexpectedly on a photograph made by the Hubble telescope, can be excellent probes of those grand forces.

The new observation is of a star that exploded 10 billion years ago, when the universe was a quarter of its present age, and when scientists theorize the cosmological constant, often called "dark energy," was less powerful than ordinary gravity, the opposite of what prevails today.

As a result, the expansion of the universe was slowing at that time. This deceleration means that the star was closer to Earth when it exploded than it otherwise would have been - a fact discernible in its unusual brightness.

Astronomers said it is twice as bright as it would have been under competing theories about the universe.

A team led by two astrophysicists, Dr. Adam G. Riess of the Space Telescope Science Institute in Baltimore and Dr. Peter Nugent of Lawrence Berkeley National Laboratory, analyzed the observations. Riess said the measurement "nails the existence of the dark energy."

`Important discoveries'

Dr. Michael S. Turner, an astrophysicist at the University of Chicago who was not involved in the work, called the dark energy "one of the most important discoveries in all of science."

"If Einstein were around today, he would get another Nobel Prize for his prediction of repulsive gravity," Turner said.

He added that the emphasis would shift to a search for the source of the energy - a problem that so far has completely stumped theoretical physics - and attempts to observe more and more distant supernovas in order to pin down the precise characteristics of the dark energy.

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