New stars born of galactic crash Hubble telescope captures images of deep-space collision

October 22, 1997|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

Dramatic new photographs from the Hubble Space Telescope have revealed the stellar fireworks at the heart of a galactic smashup.

The views of the colliding Antennae galaxies are yielding clues to the formation and evolution of galaxies and the origins of globular star clusters that have long puzzled astronomers.

And, with the nearby Andromeda galaxy headed in our direction, said Hubble astronomer Dr. Bradley Whitmore, "we might be looking at what the future fate is for our own Milky Way galaxy."

For decades, astronomers believed the universe was filled with a serene array of pinwheel-shaped spiral galaxies, such as Andromeda and the Milky Way, and foggy-looking elliptical galaxies, which have little clear structure.

But the more astronomers looked, the more examples they found of what looked like galaxies being disrupted or torn apart by collisions.

Since the late 1960s, increasingly sophisticated computer simulations of how colliding galaxies would react to each other came to bear a striking resemblance to what astronomers were seeing.

Most strikingly, it appeared that a collision between two spiral galaxies would rob both objects of their pinwheel structure and merge them into what looks like an amorphous elliptical galaxy.

If that's true, spiral galaxies should be a diminishing species in the universe, while elliptical galaxies become more numerous.

And when astronomers compare the ratio of spiral and elliptical galaxies in the nearby universe with that in the most distant regions -- closest in time to the origins of the universe -- that's just what they find.

So, at least some elliptical galaxies must be the remnants of the collisions of spiral galaxies.

Dr. Anne Kinney of Johns Hopkins University noted that most of the spiral galaxies that survive today seem to be "loners," spared so far by sheer distance from their nearest potential threats.

In a universe that scientists say has been expanding since the Big Bang, the collisions of galaxies would seem impossible.

But neighboring galaxies are bound together by gravity. Movement within those galactic clusters can lead to collisions, even as the clusters are moving apart.

And even when galaxies do collide, the stars within them are generally too far apart to crash into each other.

It's the thin gases between stars and the stars' gravitational fields that are colliding in a vast galactic "do-si-do."

Through telescopes on the ground, the Antennae galaxies look like some sort of glowing white insect with two long arcs of light resembling antennae.

The Hubble photographs -- snapped by a team led by Whitmore and Dr. Francois Schweizer, of the Carnegie Institution in Washington, D.C. -- are 10 times sharper than those taken from Earth and reveal far more.

"For the first time, astronomers are able to study in detail the processes that go on in these collisions," said Dr. Edward Weiler, NASA's Hubble project scientist.

The pictures reveal that the "insect's" body -- thousands of light-years across -- is composed of the swirling cores of two spiral galaxies.

The "antennae" are arcs of stars flung away from the cores by the gravitational forces unleashed in the collision. Computer simulations suggest they eventually will fall back into the core.

The central region is filled with more than 1,000 clusters of hot, young stars created by the intense heat and pressure of the galaxies' colliding gases. Some of the starlight from the collision is obscured by dark lanes of dust, or dimmed and reddened by the dust's filtering effects.

Astronomers are especially intrigued by the globular clusters -- each a densely packed spherical glob of perhaps 100,000 hot, young stars.

Some astronomers had argued that all such star clusters dated from the original formation of the galaxies. Hubble's images reveal they can also form in galactic pileups.

The gases of the colliding galaxies crash together into dense clouds of molecular hydrogen. The clouds then collapse under the pressure of their own gravity and ignite to form hot, new stars.

Whitmore believes he can measure the color and brightness of globular star clusters in colliding galaxies and calculate how long ago the collision began.

The crash of the Antennae galaxies is believed to have begun 50 million years before the collision reached the stage captured by Hubble. The galaxies are 63 million light-years from Earth.

Our Milky Way galaxy may be in the path of the Andromeda galaxy, now 2.2 million light-years from Earth and closing at about 300,000 mph. (A light-year is the distance light travels in one year, about 5.9 trillion miles.)

Andromeda will grow larger and brighter in the sky and get here in about 5 billion years, scientists say.

A head-on collision will ignite millions of new stars, most in brilliant blue clusters, while Andromeda's gravitational pull tears apart the familiar band of dust and stars that forms our nighttime view of the Milky Way.

Pub Date: 10/22/97

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