M27, also called the "Dumbbell Nebula," is a planetary nebula.
It consists of light (mostly at 500.7 nm wavelength) emitted by "double
ionized" oxygen atoms (i.e., [O III], having two electrons stripped off
the atom by short wavelength starlight). This is the first planetary
nebula to be discovered (Messier, 1764). It is located about 1200
light eyars away, and the central star creating it exploded about 3500
years ago (Earth time). It must have appeared as a bright star (in
the constellation Vulpecula) at the time of the great civilizations in
Egypt and China (and a few centuries after the Minoan civilization was
decimated by the volcanic eruption of Thera).
Here's a wide angle image of M27.
Figure 1. M27, FOV = 86 x 42 'arc. [Megrez 80mm aperture,
SBIG ST8XE CCD; LRGB exposures 2.6, 1.5, 2.5 and 5.3 minutes; Hereford
Arizona Observatory; 2006.10.03 UT]
Figure 2. M27 has a dimesions of 5.2 x 7.9 'arc in this image. Note the blue star at the center, whose explosion created the expanding nebula. The green color is from oxygen atoms that have had two electrons stripped off by the central star's ultraviolet ionizing radaiation (it's when the electrons recombine with the ionized atom that the green light is emitted). The red regions on the edges are from a different process. Here the interstellar medium is impeding the outward flow of the exploded star's exploded shell, and energy from these atom-with-atom impacts (actually, "near misses") cause the red light emission (I think). It has been suggested that we are viewing a ring of material edge on, with the two red regions demarking the edges of the ring, and that if we could view this nebula from another direction (such as from the upper-right) we would see a ring-like appearance, similar to that of the famous Ring Nebula of Lyra" (M57). Notice the different colors (temperatures) of the other foregraound and background stars. The imaged area is 16.3 x 14.5 'arc, with north at the top. [Meade LX200 10-inch SCT, SBIG ST-8E CCD, RGBL (3 4-minute Red and Green exposures,6 4-minute Blue exposures and 4 4-minute clear filter exposures for Luminance; cropped, 2002.06.22Z, Santa Barbara, CA residence]
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This site opened: June 20, 2002. Last Update: October 03, 2006