The glowing gas cloud, called Hubble-V, has a diameter of about 200 light-years. A faint tail of nebulosity trailing off the top of the image sits opposite a dense cluster of bright stars at the bottom of the irregularly shaped nebula.

NASA's Hubble Space Telescope's resolution and ultraviolet sensitivity reveals a dense knot of dozens of ultra-hot stars nestled in the nebula, each glowing 100,000 times brighter than our Sun.

These youthful 4-million-year-old stars are too distant and crowded together to be resolved from ground-based telescopes. The small, irregular host galaxy, called NGC 6822, is one of the Milky Way's closest neighbors and is considered prototypical of the earliest fragmentary galaxies that inhabited the young universe. The galaxy is 1.6 million light-years away in the constellation Sagittarius.

Hubble's spectacular resolution allowed a group of European and American astronomers to pinpoint individual stars in this crowded region and measure their brightness and temperatures. (Hubble-V represents one of two star-birth regions studied by the astronomers.)

They made their extensive analysis because of the telescope's ability to detect ultraviolet light, which is emitted by the hottest young stars. Their analysis has provided a better understanding of the populations of stars inside the cloud.

Hubble's sharp "eye" also allowed the astronomers to estimate the temperatures, brightness, ages, and masses of many stars. From this information, the astronomers determined that many of the stars formed at the same time.

The hot, massive stars emit a tremendous amount of radiation, which sculpted and illuminated the large gas cloud in which the stars were born. The cloud is actually composed of several "bubbles" of gas blown by the hefty stars. The hot radiation also energizes the gas, making it glow.

Besides unleashing powerful ultraviolet radiation, the massive stars also lose a significant amount of mass in "stellar winds." These winds travel at supersonic speeds (up to 6.7 million miles an hour or 10.8 million kilometers an hour), carrying away up to more than a solar mass per star every million years.

The winds slam into the surrounding gas cloud, and may play a major role in triggering star formation of smaller-mass stars. The young stellar families in Hubble-V are revealing the exact roles of all the stars in a stellar breeding ground. Hubble-V resides in a galaxy called NGC 6822, 1.6 million light-years away.

Why are these very massive stars so important?
The interiors of massive stars - unlike those of most stars, including the Sun - reach high enough temperatures to transform through nuclear fusion great quantities of primordial elements, such as hydrogen and helium, into heavier elements. Therefore, they are responsible for producing all the existing oxygen, carbon, nitrogen, silicon, and calcium - just to name a few very familiar, life-sustaining elements.

And they do so very effectively, too.

A very massive star completes its life cycle in about 10 million years (1,000 times faster than the Sun). As a massive star reaches the end of its life, it releases most of its processed material back into space by exploding as a supernova or by shedding it more gently, forming the delicate shells of a planetary nebula.

The Hubble-V image data was taken with Hubble's Wide Field Planetary Camera 2 (WFPC2) by two science teams: C. Robert O'Dell of Vanderbilt University and collaborators, and Luciana Bianchi of Johns Hopkins University and Osservatorio Astronomico, Torinese, Italy, and collaborators.

This color image was produced by The Hubble Heritage Team (STScI). A Hubble image of Hubble-X, another intense star-forming region in NGC 6822, was released by The Heritage Team in January 2001.

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