The Anti-center shell is the name of a region in space emitting 21 cm radiation near the anticenter of the Milky Way Galaxy in the constellation Auriga. It is located at 06h 27m -15°, or l = 197°, b = +2° in galactic coordinates.[1] It is a galactic supershell (that is, a very large superbubble) within our galaxy which is spherical in shape and features jets of gas. The shell has been variously referred to as a depleted dwarf galaxy or Milky Way spiral arm in research since the feature was first observed in the 1970s. [2]
Discovered in 1970, this galactic object was subsequently claimed to be a spiral arm in 1972, a tidally-stripped galaxy in 1975, and then a high-velocity cloud in 1979.
The Milky Way's anticenter shell was described in 1975 by Christian Simonson, a University of Maryland astronomer who believed it to be a small "peanut" of a galaxy.[1] [3] Simonson's colleagues named it Snickers due to its proximity to the Milky Way, in reference to the American chocolate bars Milky Way and Snickers. Less popularly, the galaxy's anticenter superbubble is also referred to by its succinct coordinates, 0627-15.[4]
Astronomical measurement of its dimensions by radio observation is difficult due to its location near the Zone of Avoidance, the regions of the sky obscured by interstellar dust. The anticenter shell is approximately 55,000 light years (17 kpc) from the sun.[1]