A wave of star formation is crashing through the Omega Nebula, captured in infrared by NASA's Spitzer Space Telescope. The bright nebula in the middle, formally known as M17, has long been recognized as a bustling star factory. But only recently have telescopes picked up on the bursts of activity that flank it.

The dark wisps of dust to the right of the starburst make up a feature called M17 SWex, which the new image reveals as a young hotbed of star formation.

"We believe we've managed to observe this dark cloud in a very early phase of star formation before its most massive stars have ignited," said astronomer Matthew Povich of Penn State University in a press release.

Spitzer detected 488 newly forming stars in the serpentine cloud, 200 of which will become blue-white class B stars larger and hotter than the sun. Povich expects that as many as 10,000 stars are brewing below the telescope's detection limits.

But the cloud is missing the largest, hottest, bluest stars, called class O stars, which light up the neighboring nebula. A luminous bubble of gas and dust to the nebula's left also shows signs of O star activity. The bubble was blown off by much older stars that spewed radiation in their windy, wild youths.

So where are the dark cloud's O stars? A solution could come from the nebula's place in the galaxy. M17 is in the process of crossing one of the Milky Way's massive spiral arms. The higher concentration of gas and dust in the spiral arm could be compressing material in M17, triggering a cascade of star formation from the bubble to the cloud.

The stars' ages support this theory: The stars in the bubble are 2 million to 5 million years old, the bright stars in the middle are about a million years old, and the stars in the dust cloud are younger than a million years. M17 SWex's big blue stars may just need an extra nudge to come to life.

This region of the sky could give astronomers new insight into what conditions massive stars need to ignite.

"We hope people will use M17 SWex as a new laboratory for studying this exact problem of how massive star formation happens," Povich said. "Most very young clouds being studied don't have as much going on as this one does."

High-resolution images with and without labels.

Image: NASA/JPL-Caltech/Matthew Povich (Penn State). Blue represents 3.6-micrometer light and green shows 8-micrometer light, both captured by Spitzer's infrared array camera. Red is 24-micrometer light detected by Spitzer's multiband imaging photometer.

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