NGC 7184 is a barred spiral galaxy located in the constellation

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. It is located at a distance of circa 100 million

light year 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 ...

s from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

, which, given its apparent dimensions, means that NGC 7184 is about 175,000 light years across. It was discovered by William Herschel on October 28, 1783.

Characteristics

NGC 7184 has a small, bright nucleus and an elliptical

bulge __NOTOC__ Bulge may refer to: Astronomy and geography *Bulge (astronomy), a tightly packed group of stars at the center of a spiral galaxy *Equatorial bulge, a bulge around the equator of a planet due to rotation *Tharsis bulge, vast volcanic pla ...

, whose major axis is aligned with the major axis of the disk. There is a bar along the minor axis of the bulge, but the high inclination of the galaxy makes its presence uncertain. From the bar emanate two tightly wound symmetrical spiral arms that form a bright inner ring. The diameter of the ring along its major axis is 1.71 arcminutes. The arms feature

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, and as they emerge from the ring are flocculent, based on the HII distribution, while they begin to split again at the outermost part of the galaxy. Dust lanes are observed in the inner part of the disk.Sandage, A., Bedke, J. (1994), ''The Carnegie Atlas of Galaxies. Volume I'', Carnegie Institution of Washington An outlying HII region has been discovered near NGC 7184. It is located on the major axis of the optical disk, on the northeasterly receding edge. Its size is estimated to be 270 pc at the distance of the galaxy and its

Hα H-alpha (Hα) is a specific deep-red visible spectral line in the Balmer series with a wavelength of 656.28 nm in air and 656.46 nm in vacuum; it occurs when a hydrogen electron falls from its third to second lowest energy level. H-alpha ...

luminosity, 10^37.6 erg s−1. It could be an isolated extension of a spiral arm.

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 7184, SN 1984N. It was discovered visually by Robert Evans at magnitude 14, 60" east and 65" north of the nucleus on July 20, 1984. Its discovery was confirmed by T. Cragg at the

Anglo-Australian Observatory The Australian Astronomical Observatory (AAO), formerly the Anglo-Australian Observatory, was an optical and near-infrared astronomy observatory with its headquarters in North Ryde in suburban Sydney, Australia. Originally funded jointly by the U ...

. Initially it was thought to be a variable star in our galaxy, but later study of the object revealed it was indeed a supernova. It was identified as

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Nearby galaxies

NGC 7184 is the foremost galaxy of a small galaxy group known as the NGC 7184 group, which also includes NGC 7183. A satellite galaxy lies 3 arcminutes to the south, at a projected separation of 28 kpc.

References

External links

{{DEFAULTSORT:NGC 7184 Barred spiral galaxies Aquarius (constellation) 7184 UGCA objects 67904 Discoveries by William Herschel Astronomical objects discovered in 1783