Anticenter shell
Encyclopedia
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 , or l = 197°, b = +2° in galactic coordinates. 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.
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
.
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.
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.
Galactic anticenter
The galactic anticenter is a theoretical point in the sky that lies directly opposite the center of the Milky Way galaxy. Because this point is relative, it will vary depending on the location of the observer; it is not an actual fixed point in space. Most of the time, this term refers to the...
of the Milky Way Galaxy in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Auriga
Auriga (constellation)
Auriga is a constellation in the northern sky. Its name is Latin for 'charioteer' and its stars form a shape that has been associated with the pointed helmet of a charioteer. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains among the 88 modern...
. It is located at , or l = 197°, b = +2° in galactic coordinates. It is a galactic supershell (that is, a very large superbubble
Superbubble
Superbubble is the astronomical term used to describe a cavity hundreds of light years across filled with 106 K gas blown into the interstellar medium by multiple supernovae and stellar winds...
) 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
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...
or Milky Way spiral arm in research since the feature was first observed in the 1970s.
Discovered in 1970, this galactic
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
object was subsequently claimed to be a spiral arm in 1972, a tidally-stripped
Tidal stripping
Tidal stripping occurs when a larger galaxy pulls stars and other stellar material from a smaller galaxy.Galaxies NGC 2207 and IC 2163 are in the process of tidal stripping....
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
University of Maryland, College Park
The University of Maryland, College Park is a top-ranked public research university located in the city of College Park in Prince George's County, Maryland, just outside Washington, D.C...
astronomer
Astronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...
who believed it to be a small "peanut" of a galaxy
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
.
Simonson's colleagues named it Snickers due to its proximity to the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
, in reference to the American chocolate bars Milky Way
Milky Way bar
The Milky Way bar is a chocolate bar distributed by the Mars confectionery company. The American version of the Milky Way bar is made of chocolate-malt nougat topped with caramel and covered with milk chocolate and is very similar to the Mars bar sold in other countries...
and Snickers
Snickers
Snickers is a brand name chocolate bar made by Mars, Incorporated. It consists of peanut nougat topped with roasted peanuts and caramel, enrobed in milk chocolate. Snickers has annual global sales of $2 billion....
. Less popularly, the galaxy's anticenter superbubble is also referred to by its succinct coordinates, 0627-15.
Astronomical
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
measurement of its dimensions by radio observation
Radio Wave
Radio Wave may refer to:*Radio frequency*Radio Wave 96.5, a radio station in Blackpool, UK...
is difficult due to its location near the Zone of Avoidance
Zone of Avoidance
The Zone of Avoidance is the area of the night sky that is obscured by our own galaxy, the Milky Way.-Term:The ZOA was originally called the "Zone of Few Nebulae" in an 1878 paper by English astronomer Richard Proctor that referred to the distribution of "nebulae" in Sir John Herschel's General...
, the regions of the sky obscured by interstellar dust. The anticenter shell is approximately 55,000 light years (17 kpc) from the sun.