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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 investigators 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).
January 6, 2000
Image Credit: NASA and The Hubble Heritage Team (STScI)