Growing fat. The Omega nebula, seen here in infrared light, harbors the largest star-forming disk ever observed.

A Massive Star Is Born

For the first time, astronomers are witnessing the birth of a supermassive star. The observations finally confirm what theorists have thought for several years: Fat stars grow slowly from swirling disks of gas and dust, just like smaller stars such as our own sun.

There's nothing mysterious about how young, lightweight stars grow. Their gravity pulls in gas and dust from a surrounding disk. There's a potential catch, though: Once the star becomes bigger and brighter, the radiation it emits might blow away the disk, inhibiting further growth. But over the past 5 years or so, theorists figured out that the radiation escapes mainly along the rotational axis, leaving the accretion disk more or less undisturbed. All fine and good, but no one had seen a very massive star during its growth spurt.

Now they have. In this week's issue of Nature, a team led by Rolf Chini of Ruhr University in Bochum, Germany, reports the detection of a gigantic accretion disk, measuring some 3 trillion kilometers across, hidden away in the Omega nebula, a young star–forming region 7000 light-years away. The disk is by far the largest ever observed. From observations with sensitive infrared cameras at large European telescopes in Chile and with the Plateau de Bure interferometer near Grenoble, France, the team concludes that the central star already weighs in at some 20 solar masses and is still growing.

"This is probably the best case we have for an accreting massive star," says theorist Harold Yorke of NASA's Jet Propulsion Laboratory in Pasadena, California. The discovery "hardens the case for the accretion disk model."

Related sites
European Southern Observatory press release on the new find, with more pictures of the accretion disk
The ISAAC infrared camera at the European Very Large Telescope
The Plateau de Bure interferometer