‘Attractor’ Theory Gains Adherents : The universe: Astronomers say they have proved the existence of a mysterious gravitational force tugging at our galaxy. Controversy remains, but other scientists say they also found evidence of the phenomenon.

Scientists said Thursday they have proved that a mysterious gravitational field is forcing our galaxy to streak toward a distant point in the southern sky at nearly 400 miles per second.

The existence of the “Great Attractor” was first postulated in 1987 by astronomers Alan Dressler of the Carnegie Institution and Sandra Faber of UC Santa Cruz, along with five colleagues who have been branded the “Seven Samurai” because of their slashing attack on conventional theory.

The controversial announcement immediately plunged the scientists into debate with many of their colleagues who doubted that the Great Attractor--as Dressler named it--existed. But the scientists returned to the fray this week during the winter meeting of the American Astronomical Society, armed with evidence that supports their original contention that a giant region of dense mass is pulling other galaxies toward it over a vast region of space.

In their recent observations, Dressler and his colleagues conclude that more than a hundred galaxies are being influenced by the huge gravitational field. Other teams of scientists, including one led by Robert A. Schommer of Rutgers University, have developed independent evidence that the Great Attractor is even greater than had been thought.

The center of Great Attractor is about 150 million light years away, the scientists reported. (A light year is the distance light travels in a year, nearly 6 trillion miles.)

Despite the fact that the Great Attractor is so far away, its gravitational field is so powerful that it is tugging on galaxies that lie hundreds of millions of light years away, the scientists said.

And therein lies a mystery.

Scientists have long theorized that the universe is smooth and reasonably homogeneous, and they see no reason why it should have giant “lumps” of concentrated matter. And there is at this point no clear understanding of just what the material is that gives the Great Attractor its enormous mass.

The discovery was “incompatible with the smoothness of the universe’s background radiation,” Dressler said. “Now we know we have found a very large lump,” and that has sent theorists back to their computers.

Dressler and his colleagues also believe the Great Attractor is not unique and that there are probably many other similar regions throughout the universe. “The universe seems to be getting lumpier and lumpier,” said Schommer, whose work supports the earlier findings.

The discovery of the Great Attractor was announced in 1987 when the “Seven Samurai” had very little data to back up their claim. The astronomers had been surveying a large segment of the sky, visible only from the Southern Hemisphere, when they discovered that some galaxies were moving at an astonishing speed toward some unseen object.

The scientists were not sure what was causing the strange movement, and they were hampered by the fact that they were able to measure the movement of only a few nearby galaxies. Dressler said Thursday they were particularly concerned that they had not been able to determine if galaxies on the other side of the Great Attractor were being pulled back.

But in the last couple of years he and Faber have studied 139 additional galaxies in the region and found evidence that all are influenced by the Great Attractor. Some on the opposite side appear to be “backfalling” toward the Great Attractor, and those located near its center show the least movement of all--as expected--because they are already trapped in the middle of the powerful gravitational field.

That does not mean that galaxies captured by the Great Attractor are banging into each other, Dressler said. Distances are so great and galaxies are scattered so far apart that collisions are probably very rare.

In addition, the universe is expanding at such an enormous rate that even most galaxies that are moving toward the center of the Great Attractor are actually getting farther apart. The movement toward the Great Attractor is actually a “perturbation” in the otherwise smooth expansion of the universe, Dressler said.

“It’s not a big traffic problem yet and it may never be unless the universe starts to contract,” he added.

As for what gives the Great Attractor its enormous pull, no one knows for sure. Several scientists speculated that it is probably matter that cannot be seen.

Scientists know that most of the universe is invisible, because the movement of galaxies reveals they have far more mass than indicated by the light they give off.

One of the great unsolved mysteries of astronomy today is a clear understanding of the exact nature of that unseen mass.

The Great Attractor has complicated the picture considerably. No one knows what gives it its great mass, and no one knows why there should be such a beast at all.

But the Seven Samurai believe the evidence now shows it is real.