Some of the night sky's most spectacular nebulas involve giant clouds of hydrogen gas (termed H II regions), where massive young stars have illuminated their surroundings with intense, ultraviolet-rich light. Once ionized, the gas glows with the unmistakable crimson of hydrogen-alpha emission at a wavelength of 656 nm.
Many of these brilliant cotton-candy whorls lie not in the Milky Way proper but rather 160,000 light-years away in the Large Magellanic Cloud.
A stunning example is LHA 120-N 11, known more informally as N 11 or the Bean Nebula. It ranks as the second largest star-forming region in the LMC, behind 30 Doradus, the Tarantula Nebula. (Historical footnote: LHA 120-N 11 was first cataloged in 1956 by the late Karl Henize, an astronomer-turned-astronaut.)
Recently Jesús Maíz Apellániz (Astrophysics Institute of Andalucía, Spain) used the Hubble Space Telescope's Advanced Camera for Surveys to capture this stunning, 6-arcminute-wide portion of the much-larger nebula.
It beautifully illustrates the sequence of events that occurs in such regions. Near the bottom is a cluster massive blue-white stars, spectral types O and B, whose stellar winds and radiation have pushed away the residual gas to create a relatively clear pocket. As this ejected gas moves outward, it collides with surrounding dense clouds, causing them to collapse and start to form new stars. These newborns then light up their surroundings.
This isn't the first time astronomers have targeted N 11 with HST. A series of images taken in 1999 with the observatory's Wide Field Planetary Camera 2 were made available in 2004 as part of the Hubble Heritage series. But the new ACS views reveal much finer details.