Photo may prove black holes exist, astronomers say

November 20, 1992|By Douglas Birch | Douglas Birch,Staff Writer

WASHINGTON -- Astronomers surveying a small group of bright, nearby galaxies with the Hubble Space Telescope said yesterday they have struck intergalactic pay dirt: the best snapshot yet of huge clouds of dust and gas that may be spiraling into a black hole.

And if NASA's 1993 Space Shuttle mission to repair the Hubble succeeds, astronomers plan to hunt inside the Frisbee-shaped cloud for what could be the first direct evidence that black holes exist.

"We haven't seen a black hole itself," cautioned Dr. Walter J. Jaffe, an American astronomer at the Leiden Observatory in the Netherlands, who led the observation. "But we've seen as close to a black hole as we've ever seen before."

"It's something that's almost too good to be true," said Bruce Margon, chairman of the astronomy department at the University of Washington, who studied the new data. He called the image "almost an artist's conception" of the region surrounding a black hole.

A black hole is a dimensionless point in space so tightly packed with matter that nothing, not even light, can escape the grip of its gravity. It sits in the center of an "event horizon," a sphere of absolute darkness where, once light or matter falls in, it can never escape.

el,.5l Working with Holland C. Ford of Johns Hopkins University and other researchers, Dr. Jaffe pointed Hubble at the core of a galaxy in the Virgo cluster of about 3,000 galaxies, about 60 million light years away.

Astronomers already knew that the elliptically-shaped galaxy, called NGC 4261, produces a lot of radio energy and is squirting out two enormous jets of very hot material in opposite directions, like a tube of toothpaste open at both ends.

They suspected that the engine churning out that energy was a spinning cloud draining into a black hole. But the galaxy's center is too distant to be seen by ground-based telescopes.

Earlier this year, Dr. Ford used Hubble to photograph the outline of a donut-shaped cloud or "accretion disc" surrounding a suspected black hole in another galaxy.

But the view was edge on and the center of the cloud -- where the black hole is thought to sit -- was not visible.

Luckily for astronomers, NGC 4261's cloud is tilted toward the Earth in such a way that its center, top and one edge are clearly visible.

"The pictures . . . give us the best look we've ever had at the inner workings of the nuclear engine at the center of an active galaxy," Dr. Jaffe said.

"I think we've seen an accretion disc, and that's a big deal," said Anne L. Kinney, an astronomer with Baltimore's Space Telescope Science Institute.

The hole itself cannot be seen. But its existence may be betrayed by the tug of its gravity on nearby stars or other objects. And matter falling into the hole would be accelerated, compressed and heated tens of millions of degrees by the crushing gravity.

Where a circling cloud is feeding a voracious black hole, scientists think the hole spews out jets of material on both sides.

Dr. Jaffe said NGC 4261 may harbor a modest black hole with a mass about 10 million times that of the Sun. The event horizon might fill the distance between the Earth and the Sun, about 93 million miles.

That's about 100,000 times too small to be seen directly by Hubble, even if its optics were perfect. The cloud is much larger, about 300 million light-years across. (A light year, the distance light travels in a year, is about 6 trillion miles.)

Dr. Jaffe and Dr. Ford said that, after NASA's Hubble repair mission in December 1993, they hope to point the telescope back at the center of NGC 4261 and make very precise measurements of the movement of dust and gas to within a few dozen light years of the black hole.

If Hubble's vision improves and those measurements work, astronomers will be able to calculate the speed of the inflowing matter.

Once they know the speed, they can determine the mass of the object at the center. If there is an enormous amount of matter in a tiny space, scientists will have good evidence for a black hole.

While the Hubble image confirmed many predictions about black holes, it challenged some others. For one thing, Dr. Jaffe said, the cloud is thinner than expected -- most were expected to resemble fat donuts.

What created the spinning cloud? Dr. Jaffe said it may have been triggered by the collision of two galaxies. And he said there is evidence that the cloud may not be in the center of the galaxy, but wobbling around -- perhaps as a result of the earlier collision.

Daniel W. Weedman, an astronomy professor at Pennsylvania State University and a black hole skeptic, emphasized that the Hubble picture does not prove the existence of these weird objects.

But he said the Hubble picture gives the best view yet of whatever it is at the center of some galaxies that produces enormous amounts of energy.

"We've really seen into the fiery furnace," he said.

Baltimore Sun Articles
|
|
|
Please note the green-lined linked article text has been applied commercially without any involvement from our newsroom editors, reporters or any other editorial staff.