Arcs,Birth and a Disk in the Sky

By MICHAEL D. LEMONICK

Even the most jaded sky watchers were intrigued last week by three remarkable discoveries reported at the American Astronomical Society meeting in Pasadena, Calif. Two of the finds lend support to current theories about the formation of planets and of galaxies, immense islands of hundreds of billions of stars. But a third -- two gigantic, well-defined arcs of light, as well as fragments of another -- cannot be explained to anyone's satisfaction.

The mysterious arcs, each four to seven times as long as the diameter of the Milky Way, curve around clusters of galaxies that lie some 3 billion light- years* from earth. Astronomers Vahe Petrosian of Stanford University and Roger Lynds of Arizona's Kitt Peak National Observatory, who discovered the arcs, believe each consists of some 100 billion stars but cannot explain the shape. "What gives us a headache," says Petrosian, "is that they are so, so perfect."

Some scientists suggest that each arc might have been formed as a result of a huge explosion within a nearby galaxy. Expanding shock waves from this blast would have compressed surrounding gases, clumping molecules together and setting off the process by which stars form. But that process should produce bubbles -- that is, voids surrounded by a spherical "skin" of stars. These arcs are virtually two-dimensional strands of stars. Besides, astronomers have not detected enough gas in the area to have formed structures as large as the arcs.

Another possibility is that the arcs were once galaxies but were somehow stretched out of shape by the gravitational pull of other galaxies. Yet gravity strong enough to distort a galaxy would be unlikely to leave behind anything as well organized as the observed arcs. A third explanation -- that the arcs condensed from

jets of matter emitted from the core of one of the galaxies -- is even more farfetched.

Less spectacular, perhaps, was the discovery of a galaxy in the act of being born, a celestial infant long sought by astronomers. The one they finally found, called 3C 326.1, is exceedingly faint; it has been known for about 30 years, but only as an unseen source of radio waves.

The invisible object piqued the interest of Berkeley Astronomer Hyron Spinrad, known for his studies of very dim, faraway galaxies and quasars. Last spring Spinrad and his team first pinpointed 3C 326.1's position with New Mexico's Very Large Array radio telescopes; then they aimed powerful optical telescopes at the spot and discovered a glowing object about 12 billion light- years from earth. Later analysis of light from 3C 326.1 revealed that it was a newborn galaxy, three times as long as the diameter of the Milky Way. At the time the light viewed by Spinrad left 3C 326.1, which was 12 billion years ago, the new galaxy was forming sun-size stars at the rate of about 3,000 to 5,000 a year. But it still consisted largely of ionized hydrogen gas that & would eventually condense into billions of additional stars. It was a late bloomer, Spinrad says, because astronomers think most galaxies formed 14 billion years ago.

Closest to home -- in the Milky Way itself -- Cornell and Caltech astronomers have found what may be the early stages in the formation of a new solar system, showing for the first time that a dust disk surrounding a sun- size star orbits the star in an orderly fashion. Such disks, initially found in the early 1980s, have been touted as the precursors of planetary systems. This discovery makes the claim a notch less speculative and suggests that stars with planets may be quite common.

*A light-year, the distance that light travels in one year, is about 6 trillion miles.

With reporting by Charles Pelton/San Francisco