SAN DIEGO--The Hubble Space Telescope has snapped a striking photo of a ring of stars bursting to life near the center of a galaxy. Glowing like a chain of roadside flares, the ring is the best example yet of the symmetric waves of star formation that can race through galaxies, say astronomers who released the picture here today at a meeting of the American Astronomical Society.
Many galaxies form graceful spirals and other dynamic star patterns as they swirl over billions of years. One common pattern is a dense "bar" of stars within the galaxy that bisects it. Such bars can pulse through galaxies and spawn great arcs of stars via interactions that scientists don't yet understand. Two decades ago, astronomer G. Fritz Benedict of the University of Texas, Austin, recognized that the barred galaxy NGC 4314, about 40 million light-years away in the constellation Coma Berenices, offered a chance to examine that phenomenon in detail. The galaxy is close enough to resolve its innermost regions, and it's oriented face-on, providing an unobstructed view of the entire structure.
Hubble's picture, taken in December 1995, was even more revealing than Benedict had expected. "I've waited 18 years for this image," he says. "It's an immensely powerful tool to study star formation." All of NGC 4314's star birth occurs in a small ring 1000 light-years across, just a few percent of the galaxy's size. That tiny crucible of activity, Benedict says, may be a unique feature of NGC 4314. The colors of the new stars show they all formed within the last few million years. Wispier blue stars outside the ring arose perhaps 200 million years ago, hinting that the starry ring may be shrinking toward the galaxy's core, as a wave of star formation ripples inward. Benedict's team also plans to analyze dark dust lanes plunging into the galactic core for clues to the innermost galaxy's rotation
The star bar must be driving the frenzied ring of star birth in NGC 4314, says astronomer Ronald Buta of the University of Alabama, Tuscaloosa. "Rings and bars appear intimately connected in many galaxies, and this is a very fine case," says Buta. Gravitational instabilities caused by the bar may force gas clouds to collide at a particular radius within the galaxy, he suspects. Such collisions could trigger the clouds to collapse and spawn new stars.