NGC 3631 is a

spiral galaxy Spiral galaxies form a galaxy morphological classification, class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''

Ursa Major Ursa Major, also known as the Great Bear, is a constellation in the Northern Sky, whose associated mythology likely dates back into prehistory. Its Latin name means "greater (or larger) bear", referring to and contrasting it with nearby Ursa M ...

. It is located at a distance of about 35 million

light year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...

s from Earth, which, given its apparent dimensions, means that NGC 3631 is about 60,000 light years across. It was discovered by

William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...

on April 14, 1789. It is a

grand design spiral galaxy A grand design spiral galaxy is a spiral galaxy with prominent and well-defined continuous spiral arms, as opposed to multi-arm, patchy and flocculent spirals which have subtler structural features. The spiral arms of a grand design galaxy exten ...

seen face on.

Characteristics

NGC 3631 is a

and features two principal

spiral arm Spiral arms are a defining feature of spiral galaxies. They manifest as spiral-shaped regions of enhanced brightness within the galactic disc. Typically, spiral galaxies exhibit two or more spiral arms. The collective configuration of these arms i ...

s, which begin near the center. The two main arms branch into secondary arms with lower surface brightness. The galaxy shows moderate-to-high star formation rate and bright

HII region An H II region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light year ...

s are present in all the arms. The star formation rate of the galaxy is 4.6 per year.

Halton Arp Halton Christian "Chip" Arp (March 21, 1927 – December 28, 2013) was an American astronomer. He is remembered for his 1966 book ''Atlas of Peculiar Galaxies'', which catalogued unusual-looking galaxies and presented their images. Arp was als ...

observed "straight arms", and an "absorption tube crossing from inside to outside of southern arm" and added the galaxy to his

Atlas of Peculiar Galaxies The ''Atlas of Peculiar Galaxies'' is a Astronomical catalog, catalog of peculiar galaxies produced by Halton Arp in 1966. A total of 338 galaxies are presented in the atlas, which was originally published in 1966 by the California Institut ...

. At inclination of 17 degrees, the galaxy is seen nearly face on. The HI imaging shows the spiral arms distinguished well and HI is also detected in most of the interarm regions. The atomic hydrogen is detected mostly within the limits of the optical disc but also extends one and a half times the radius of the optical disk. The hydrogen forms streaming motions near the spiral arms. The gas features two anticyclonic and four cyclonic vortices, rotating with the spiral pattern. The anticyclones are caused by the differential rotation and the cyclones are the result of a high amplitude in the density wave. The centres of the anticyclones are located between the observed spiral arms and the cyclones lie close to the observed spirals. NGC 3631 has weak diffuse

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

emission. There are six candidates ultraluminous X-ray sources in disk of the galaxy, two which have an optical counterpart. The nucleus of the galaxy hosts a

supermassive black hole A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions, of times the mass of the Sun (). Black holes are a class of astronomical ...

with mass 10^7.4 (25 million) , based on Ks bulge luminosity.

Supernovae

Four

supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...

e have been discovered in NGC 3631: * SN 1964A (type unknown, mag. 17) was discovered by Paul Wild on 4 February 1964. * SN 1965L (type unknown, mag. 16) was discovered by Paul Wild on 25 September 1965. ote: some sources incorrectly list the discovery date as 29 September 1965.* SN 1996bu ( type II, mag. 17.3) was discovered by Reiki Kushida on 14 November 1996. * SN 2016bau ( type Ib, mag. 17.8) was discovered by Ron Arbour on 13 March 2016, before it reached maximum light. It was also observed in radio waves by the VLA as a radio source with a flux density of 1.0 ± 0.03 mJy at 8.6 GHz.

Nearby galaxies and group

NGC 3631 forms a small group with NGC 3657, which is part of the north Ursa Major groups, which is part of the Ursa Major Cloud, which is part of the

Virgo Supercluster The Local Supercluster (LSC or LS), or Virgo Supercluster is a formerly defined supercluster containing the Virgo Cluster and Local Group, which itself contains the Milky Way and Andromeda galaxies, as well as others. At least 100 galaxy group ...

. According to A.M. Garcia, NGC 3631 is part of the NGC 3631

galaxy group A galaxy group or group of galaxies (GrG) is an aggregation of galaxies comprising about 50 or fewer gravitationally bound members, each at least as luminous as the Milky Way (about 1010 times the luminosity of the Sun); collections of galaxi ...

(also known as LGG 241). This group includes at least 10 galaxies, including NGC 3657, NGC 3718, NGC 3729, NGC 3913,

NGC 3972 NGC 3972 is a spiral galaxy located in the northern constellation of Ursa Major. It was discovered by William Herschel on April 14, 1789. This galaxy is located 66 million light years away and is receding with a heliocentric radial velocity ...

, NGC 3998, UGC 6251, UGC 6446, and UGC 6816.

Gallery

NGC3631 - SDSS DR14.jpg, NGC 3631 (SDSS DR14) NGC 3631 2MASS.jpg, NGC 3631 by

2MASS The Two Micron All-Sky Survey, or 2MASS, was an astronomical survey of the whole sky in infrared light. It took place between 1997 and 2001, in two different locations: at the U.S. Fred Lawrence Whipple Observatory on Mount Hopkins, Arizona, and ...

NGC3631-hst-R814G606B450.jpg, HST image of NGC 3631. NGC 3631 GALEX WikiSky.jpg, NGC 3631 by

GALEX Galaxy Evolution Explorer (GALEX or Explorer 83 or SMEX-7) was a NASA orbiting space telescope designed to observe the universe in ultraviolet wavelengths to measure the history of star formation in the universe. In addition to paving the way ...

References

External links

{{Ngc40 Unbarred spiral galaxies Ursa Major NGC 3631 Group 3631 06360 34767 027 Astronomical objects discovered in 1789 Discoveries by William Herschel