 Fireworks
of Star Formation Light Up a Galaxy
Newly released images obtained with NASA's Hubble
Space Telescope in July 1997 reveal episodes of star formation that
are occurring across the face of the nearby galaxy NGC 4214.
Located some 13 million light-years from Earth, NGC
4214 is currently forming clusters of new stars from its interstellar
gas and dust. In the Hubble image, we can see a sequence of steps
in the formation and evolution of stars and star clusters. The picture
was created from exposures taken in several color filters with Hubble's
Wide Field Planetary Camera 2.
NGC 4214 contains a multitude of faint stars covering
most of the frame, but the picture is dominated by filigreed clouds
of glowing gas surrounding bright stellar clusters.
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. Each cloud fluoresces because
of the strong ultraviolet light emitted from the embedded young
stars, which have formed within them due to gravitational collapse
of the gas.
Young, hot stars have a whitish to bluish color in
the Hubble image, because of their high surface temperatures, ranging
from 10,000 up to about 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.
Moving to the lower left from the youngest clusters,
we find 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 NGC 4214. This object is a cluster of hundreds
of massive blue stars, each of them more than 10,000 times brighter
than our own 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 yet another
new generation of stars, even as the clusters visible today gradually
fade away.
The faint stars covering most of the picture are much
older than the bright blue supergiants, and show us that episodes
of star birth have been occurring in NGC 4214 for billions of years.
The principal astronomers are: John MacKenty, Jesus
Maiz-Apellaniz (Space Telescope Science Institute), Colin Norman
(Johns Hopkins University), Nolan Walborn (Space Telescope Science
Institute), Richard Burg (Johns Hopkins University), Richard Griffiths
(Carnegie Mellon University), and Rosemary Wyse (Johns Hopkins University).
Image Credit: NASA
and The Hubble Heritage Team (STScI)
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STScI-PRC00-01
