__NOTOC__ NGC 2207 and IC 2163 are a pair of colliding spiral galaxies about 80 million

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distance, astronomical distances and is equivalent to about 9.46 Orders of magnitude (numbers)#1012, trillion kilometers (), or 5.88 ...

s away in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the earliest constellation ...

Canis Major Canis Major is a constellation in the southern celestial hemisphere. In the second century, it was included in Ptolemy's 48 constellations, and is counted among the 88 modern constellations. Its name is Latin for "greater dog" in contrast ...

. Both galaxies were discovered by

John Herschel Sir John Frederick William Herschel, 1st Baronet (; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor, experimental photographer who invented the blueprint and did botanical wo ...

in 1835. The larger spiral, NGC 2207, is classified as an

intermediate spiral galaxy An intermediate spiral galaxy is a galaxy that is in between the classifications of a barred spiral galaxy and an unbarred spiral galaxy. It is designated as SAB in the galaxy morphological classification system devised by Gerard de Vaucouleu ...

exhibiting a weak inner ring structure around the central bar. The smaller companion spiral, IC 2163, is classified as a

barred spiral galaxy A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in about two thirds of all spiral galaxies, and generally affect both the motions of stars and interstellar gas within spiral galaxies ...

that also exhibits a weak inner ring and an elongated spiral arm that is likely being stretched by

tidal force The tidal force is a gravitational effect that stretches a body along the line towards the center of mass of another body due to a gradient (difference in strength) in gravitational field from the other body; it is responsible for diverse phenomen ...

s with the larger companion. Both galaxies contain a vast amount of dust and gas, and are beginning to exhibit enhanced rates of

star formation Star formation is the process by which dense regions within molecular clouds in The "medium" is present further soon.-->interstellar space

, as seen in infrared images. NGC 2207 is in the process of colliding and merging with IC 2163. But unlike the Antennae or the Mice Galaxies, they are still two separate spiral galaxies. They are only in the first step of colliding and merging, with NGC 2207 being in the process of tidally stripping IC 2163. Soon they will collide, probably looking a bit more like the Mice Galaxies. In about a billion years time they are expected to merge and become an

elliptical galaxy An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The Real ...

or perhaps a

disk galaxy A disc galaxy (or disk galaxy) is a galaxy characterized by a galactic disc, a flattened circular volume of stars. These galaxies may or may not include a central non-disc-like region (a galactic bulge). Disc galaxy types include: * Spiral gala ...

. Four

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or whe ...

e have been observed in NGC 2207: * type Ia SN 1975a in January 1975 * type Ib SN 1999ec in October 1999 * type Ib SN 2003H—discovered halfway between the two galaxies * type II supernova SN 2013ai in March 2013 Two supernovae have been observed in IC 2136:2018lab
in IC 2136 (David Bishop) * type II SN 2018lab * unknown type SN SPIRITS17lb

References

External links

HST: A grazing encounter between two spiral galaxies
* * * {{DEFAULTSORT:NGC 2207 and IC 2163 Intermediate spiral galaxies Barred spiral galaxies Peculiar galaxies Interacting galaxies Canis Major 2207 IC objects 18749 UGCA objects Discoveries by John Herschel 18350124

See also

References

External links