Robbing the Stellar Cradle

Many fecund galaxies that glow with the birth of stars also contain ravenous black holes at their core. Astronomers have long wondered about this curious cohabitation; now the Hubble Space Telescope has provided the sharpest pictures yet of one of these stellar nurseries. The images, described in next week's issue of The Astrophysical Journal Letters, may help theorists clear up the relationship between these forces of creation and destruction.

Black holes in galactic centers suck in matter and spew out radiation. Theorists have speculated that the force of this radiation might trigger star formation by compressing interstellar gas. During a survey of galaxies with star bursts, or regions of prolific star formation, a team of astronomers from the United States, Spain, and Germany zoomed in on several galaxies with just the right orientation. "They're face-on, so we can see the structure," says Luis Colina, an astronomer with the Space Telescope Science Institute in Baltimore.

In one of these galaxies, called NGC 4303 and located about 50 million light-years away from Earth, the Hubble telescope captured swirls of glowing gas spiraling toward galactic center. Within the spiral, the astronomers found, are clusters of star formation marked by intense ultraviolet radiation. Because NGC 4303 harbors a radiation-emitting "active galactic nucleus," thought to be a massive black hole, the picture suggests that the gas and the baby stars themselves may be spiraling into the black hole.

With more measurements, "you could tell whether [the gas] is plunging toward the hole or not," says Michael Shull, an astrophysicist at the University of Colorado, Boulder. And that, he says, would confirm the feeding habits of the black hole. Tim Heckman, an astrophysicist at Johns Hopkins University, says nailing down these uncertainties should improve computer models of galaxy evolution. "It probably really requires the Hubble Space Telescope to find out," he adds.