NGC 2445 is a peculiar

ring galaxy A ring galaxy is a galaxy with a circle-like appearance. Hoag's Object, discovered by Art Hoag in 1950, is an example of a ring galaxy. The ring contains many massive, relatively young blue stars, which are extremely bright. The central region co ...

in the constellation

Lynx A lynx is a type of wild cat. Lynx may also refer to: Astronomy * Lynx (constellation) * Lynx (Chinese astronomy) * Lynx X-ray Observatory, a NASA-funded mission concept for a next-generation X-ray space observatory Places Canada * Lynx, Ontar ...

. The galaxy lies about 200 million

light years A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

away from Earth, which means, given its apparent dimensions, that NGC 2445 is approximately 100,000 light years across. It was discovered by

Édouard Stephan Édouard Jean-Marie Stephan (31 August 1837 – 31 December 1923) was a French astronomer. His surname is sometimes spelled Stéphan in some literature, but this is apparently erroneous. He was born in Sainte Pezenne (today one of the districts ...

on January 18, 1877. The galaxy interacts with another galaxy, NGC 2444, and as a result its shape is distorted and new stars are formed. CC-BY icon

This article contains quotations from this source, which is available under th
Creative Commons Attribution 4.0 Unported (CC BY 4.0)
license.

Characteristics

NGC 2445 is characterised by its distorted shape and

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

which is the result of the collision with another galaxy, NGC 2444. NGC 2444 has pulled gas away from NGC 2445 and as a result a bridge of young blue stars has formed between the two galaxies that gives the latter a triangular shape. The interaction has also created a ring of

star cluster Star clusters are large groups of stars. Two main types of star clusters can be distinguished: globular clusters are tight groups of ten thousand to millions of old stars which are gravitationally bound, while open clusters are more loosely clust ...

s and

HII region An H II region or HII 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 ...

s around the nucleus. The kinematics of the gas indicate that the ring has an age of 60 ± 15 million years. When observed in radio waves the galaxy is asymmetric, with emission being from the nucleus, three star-forming regions and a ridge towards NGC 2444. The northwestern region appears to have stronger magnetic field than the other two. Two giant

molecular cloud A molecular cloud, sometimes called a stellar nursery (if star formation is occurring within), is a type of interstellar cloud, the density and size of which permit absorption nebulae, the formation of molecules (most commonly molecular hydrogen ...

s are visible in the ¹²CO(J=1–0) emission to the west and northwest of the nucleus. In mid infrared are visible some arms connecting the ring with the nucleus. The streamers between the two galaxies are among the first in what appears to be a wave of star formation that started on the galaxy's outskirts and continued inward. Researchers estimate the streamer stars were born between 50 million and 100 million years ago. The age of the star-forming knots in the ring is calculated to be 2-8 million years. Stars no older than one million to two million years old are forming closer to the centre of NGC 2445. Observations of carbon monoxide emission indicate that NGC 2445 still has abundant gas and star formation rates will increase. Hubble Space Telescope has uncovered dark filaments of gas in the starburst galaxy's bright core. Those features may have been formed by outbursts of material, however the dust from the outbursts blankets the nucleus in the visible spectrum. When observed in radio waves the core isn't very compact and its spectrum indicates the presence of a starburst region with an age between 1.5 and 5 million years. A shell of hydrogen gas measuring 20 kiloparsecs across has been found at a projected distance of about 100 kiloparsec of the galactic system. A filament of this shells points towards the galaxies indicating that it is a

superbubble A superbubble or supershell is a cavity which is hundreds of light years across and is populated with hot (106 K) gas atoms, less dense than the surrounding interstellar medium, blown against that medium and carved out by multiple supern ...

associated with them or a

tidal tail A tidal tail is a thin, elongated region of stars and interstellar gas that extends into space from a galaxy. Tidal tails occur as a result of galactic tide forces between interacting galaxies. Examples of galaxies with tidal tails include the ...

Supernova

One

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 when ...

has been observed in NGC 2444/5, SN 2016bam. The supernova occurred between the two galaxies, about 3.5 arcseconds away from a

of NGC 2445. It was a

type II supernova A Type II supernova (plural: ''supernovae'' or ''supernovas'') results from the rapid collapse and violent explosion of a massive star. A star must have at least 8 times, but no more than 40 to 50 times, the mass of the Sun () to undergo this ...

which had magnitude 16.1 at discovery.

Nearby galaxies

NGC 2445 and NGC 2444 (which lies about one arcminute away) form a pair, known as Arp 143. The pair is part of a

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 galaxies ...

known as LGG 148. Other members of the group include the galaxies NGC 2476, NGC 2493, NGC 2524, NGC 2415, UGC 3937, and UGC 3944.

References

External links

{{Lynx (constellation) Ring galaxies Peculiar galaxies Interacting galaxies Starburst galaxies Lynx (constellation) 2445 04017 143 21776 Discoveries by Édouard Stephan Astronomical objects discovered in 1877