January 6, 2000: Pictures obtained with the Hubble telescope 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 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. Clouds of glowing gas surrounding bright stellar clusters dominate the picture.
The youngest clusters are at the lower right of the picture, where they appear as about half a dozen bright clumps of glowing gas. Each cloud glows because of the strong ultraviolet light emitted from the embedded young stars, which have formed within them due to the gravitational collapse of the gas. These hot stars also eject fast "stellar winds" moving at millions of miles per hour (thousands of kilometers per second), which plow into the surrounding gas. The radiation and wind from the young stars literally blow bubbles in the gas.
This object is a cluster of hundreds of massive blue stars, each more than 10,000 times brighter that our Sun. A vast heart-shaped bubble, inflated by the combined stellar winds and radiation pressure, surrounds the cluster. The bubble will increase in size as the most massive stars in the center reach the ends of their lives and explode as supernovae.