Astronomers zoom in on the birth of stars

Star birth is a spectacular and poorly understood process. But thanks to the ever increasing power of their instruments, astronomers are getting a tighter grip on the problem. Newly released images from the Hubble Space Telescope illustrate what's involved.

Stars form in interstellar clouds that are rich in hydrogen and some other elements. Gravity causes denser clumps within such clouds to collapse until their internal pressure and temperature are high enough to light the stellar nuclear fire.

That's what's going on in the gas cloud named N81 shown at bottom. It lies 200,000 light years away in the Small Magellanic Cloud - a satellite galaxy that accompanies our Milky Way galaxy.

N81 is only a blurry blotch in earth-based telescopes. But sharp-eyed Hubble shows a host of young stars. Their radiation illuminates surrounding material.

A long dust trail snakes across the bright background, tying itself into a knot. More stars may form here.

This broad picture is what star-birth theory predicts. But exactly what happens as gravity compresses dust and gas is unclear.

The collapsing mass flattens and spins faster and faster. How it sheds excess rotational momentum to avoid tearing itself apart is a mystery.

There is more matter than needed to form the star and any accompanying planets. How excess matter is shed also is poorly understood.

Astronomers think magnetic forces are involved. Last Year, Prof. Richard Crutcher of the University of Illinois at Urbana-Champaign reported a study of 27 interstellar clouds showing magnetic fields strong enough to do the job. He explained, "By flinging a small amount of matter outward along the magnetic field lines, the magnetic waves can remove a huge amount of angular momentum, making star formation possible."

Two series of images of newly formed stars taken over the past five years appear to show this kind of process. The stars are about 450 light-years from Earth in the Taurus-Auriga interstellar cloud. Magnetic forces of the star HH 30 are channeling narrow jets of material out through the star's north and south magnetic poles.

Moving at 200,000 to 600,000 miles an hour, the jets illuminate surrounding material. The star itself is hidden by a dust disk that cuts a dark band across the bright central part of the image.

Only dust above and below the plane of this disk is shown by the star light it reflects. The disk (pictured immediately above) is about 42 billion miles across. The image series show how the jets have changed over the past five years.

The binary star XZ Tauri shows even more spectacular development. Magnetic forces are channeling a huge bubble of material from dust around one or both stars. The image series shows the expansion of this bubble nearly 300,000 miles an hour to extend nearly 60 billion miles. Such development is what theory predicts. But Dr. Crutcher notes that the Hubble can't provide the fine grain data needed to effectively test the theory.

That requires detailed measurements of movement within their circumstellar disks themselves. He says he is looking forward to the next generation of radio telescopes, such as the international Atacama Large Millimeter Array being built in Chile. Its 64 antennas - each 12 meters (39.4 feet) across - "will be just what's needed," he says.

(c) Copyright 2000. The Christian Science Publishing Society