Fireworks of star birth light up nearby galaxy

Galaxy NGC 4214

January 11, 2000
Web posted at: 10:17 a.m. EST (1517 GMT)

(CNN) -- Bursting in brilliant yellows, reds and blues, the formation of stars in a nearby galaxy presents some spectacular celestial fireworks, as illustrated in a recently released image taken by NASA's Hubble Space Telescope.

Located 13 million light-years from Earth, the galaxy NGC 4214 is forming clusters of new stars from its interstellar gas and dust, according to NASA, which released the image this month. The Hubble snapshot reveals a sequence of steps in the evolution of stars and star clusters.

NGC 4214 contains a multitude of faint stars covering most of the frame, but the picture is dominated by clouds of glowing gas surrounding bright stellar clusters.

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The youngest of these star clusters are located at the lower right of the picture, where they appear as about half a dozen bright clumps of glowing gas. Inside the clouds, young stars, formed due to gravitational collapse of the gas, emit strong ultraviolet light.

The young, hot stars have a whitish to bluish color because of their high surface temperatures, ranging from 10,000 to 50,000 degrees Celsius.

In addition to pouring out ultraviolet light, these hot stars eject fast "stellar winds," moving at thousands of kilometers per second, which plow out into the surrounding gas.

The radiation and wind forces from the young stars literally blow bubbles in the gas. Over millions of years, the bubbles increase in size as the stars inside them grow older.

To the lower left of the youngest clusters is an older star cluster, around which a gas bubble has inflated to the point that there is an obvious cavity around the central cluster.

The most spectacular feature in the Hubble picture lies near the center of the galaxy. This object is a cluster of hundreds of massive blue stars, each of them more than 10,000 times brighter than the sun.

A vast heart-shaped bubble, inflated by the combined stellar winds and radiation pressure, surrounds the cluster. The expansion of the bubble is augmented as the most massive stars in the center reach the ends of their lives and explode as supernovae.

Deprived of gas, the cluster at the center of NGC 4214 will be unable to form further new stars, and its luminous stars will continue to go supernova and disappear.

Elsewhere in the galaxy, however, gas will start to collapse and form another generation of stars, even as the clusters currently visible gradually fade.

The faint stars covering most of the picture are much older than the bright blue supergiants and indicate that episodes of star birth have been occurring in the galaxy for billions of years.

The picture was created from exposures taken in several color filters with a Hubble camera in 1997.