Sculptor Galaxy

Template:Short description Template:Distinguish

Template:Infobox Galaxy The Sculptor Galaxy (also known as the Silver Coin Galaxy, Silver Dollar Galaxy, NGC 253, or Caldwell 65) is an intermediate spiral galaxy in the constellation Sculptor. The Sculptor Galaxy is a starburst galaxy, which means that it is currently undergoing a period of intense star formation.

ObservationEdit

Observational historyEdit

The galaxy was discovered by Caroline Herschel in 1783 during one of her systematic comet searches.<ref name="Dreyer1888">Template:Cite journal</ref><ref name="Burnhams">Template:Cite book</ref> About half a century later, John Herschel observed it using his 18-inch metallic mirror reflector at the Cape of Good Hope.<ref name="Burnhams" /> He wrote: "very bright and large (24′ in length); a superb object.... Its light is somewhat streaky, but I see no stars in it except 4 large and one very small one, and these seem not to belong to it, there being many near..."<ref name="Burnhams" />

In 1961, Allan Sandage wrote in the Hubble Atlas of Galaxies that the Sculptor Galaxy is "the prototype example of a special subgroup of Sc systems....photographic images of galaxies of the group are dominated by the dust pattern. Dust lanes and patches of great complexity are scattered throughout the surface. Spiral arms are often difficult to trace.... The arms are defined as much by the dust as by the spiral pattern."<ref name="Sandage1961">Template:Cite book</ref> Bernard Y. Mills, working out of Sydney, discovered that the Sculptor Galaxy is also a fairly strong radio source.<ref name="Burnhams" />

In 1998, the Hubble Space Telescope took a detailed image of NGC 253.<ref name="hubb">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

AmateurEdit

As one of the brightest galaxies in the sky, the Sculptor Galaxy can be seen through binoculars and is near the star Beta Ceti. It is considered one of the most easily viewed galaxies in the sky after the Andromeda Galaxy.<ref name="Burnhams"/><ref name="NSOG">Template:Cite book</ref>

The Sculptor Galaxy is a good target for observation with a telescope with a 300 mm diameter or larger.<ref name="NSOG" /> In such telescopes, it appears as a galaxy with a long, oval bulge and a mottled galactic disc.<ref name="NSOG" /> Although the bulge appears only slightly brighter than the rest of the galaxy, it is fairly extended compared to the disk.<ref name="NSOG" /> In 400 mm scopes and larger, a dark dust lane northwest of the nucleus is visible, and over a dozen faint stars can be seen superimposed on the bulge.<ref name="NSOG" /> Some people claim to have observed the galaxy with the unaided eye under exceptional viewing conditions.

FeaturesEdit

File:Three-dimensional view of ALMA observations of the outflows from NGC 253.jpg

Three-dimensional simulation of ALMA observations of the outflows.<ref>Template:Cite news</ref>

File:NGC 253.jpg

Detail of NGC 253 by Hubble Space Telescope. (Credit: HST/NASA/ESA).

The Sculptor Galaxy is located at the center of the Sculptor Group, one of the nearest groups of galaxies to the Milky Way.<ref name="karachentsev2005">Template:Cite journal</ref> The Sculptor Galaxy (the brightest galaxy in the group and one of the intrinsically brightest galaxies in the vicinity of ours, only surpassed by the Andromeda Galaxy and the Sombrero Galaxy<ref name="Karachentsev2004">Template:Cite journal</ref>) and the companion galaxies NGC 247, PGC 2881, PGC 2933, Sculptor-dE1, and UGCA 15 form a gravitationally-bound core near the center of the group. Most other galaxies associated with the Sculptor Group are only weakly gravitationally bound to this core.<ref name="karachentsev2005" /><ref name="karachentsevetal2003">Template:Cite journal</ref>

StarburstEdit

NGC 253's starburst has created several super star clusters on NGC 253's center (discovered with the aid of the Hubble Space Telescope): one with a mass of Template:Val solar masses, and absolute magnitude of at least −15, and two others with Template:Val solar masses and absolute magnitudes around −11;<ref name="Watson1996">Template:Cite journal</ref> later studies have discovered an even more massive cluster heavily obscured by NGC 253's interstellar dust with a mass of Template:Val solar masses, an age of around Template:Val years, and rich in Wolf-Rayet stars.<ref name="Kornei2009">Template:Cite journal</ref> The super star clusters are arranged in an ellipse around the center of NGC 253, which from the Earth's perspective appears as a flat line.<ref>Template:Cite journal</ref>

Star formation is also high in the northeast of NGC 253's disk, where a number of red supergiant stars can be found, and in its halo there are young stars as well as some amounts of neutral hydrogen. This, along with other peculiarities found in NGC 253, suggest that a gas-rich dwarf galaxy collided with it 200 million years ago, disturbing its disk and starting the present starburst.<ref name="Davidge2010">Template:Cite journal</ref>

As happens in other galaxies suffering strong star formation such as Messier 82, NGC 4631, or NGC 4666, the stellar winds of the massive stars produced in the starburst as well as their deaths as supernovae have blown out material to NGC 253's halo in the form of a superwind that seems to be inhibiting star formation in the galaxy.<ref name="Bolatto2013">Template:Cite journal</ref>

Novae and SupernovaeEdit

Although supernovae are generally associated with starburst galaxies, only one has been detected within the Sculptor Galaxy. SN 1940E (type unknown, mag. 14)<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> was discovered by Fritz Zwicky on 22 November 1940, located approximately 54″ southwest of the galaxy's nucleus.<ref name="barbonetal1984">Template:Cite journal</ref>

NGC 253 is close enough that classical novae can also be detected. The first confirmed nova in this galaxy was discovered by BlackGEM at magnitude 19.6 on 12 July 2024, and designated AT 2024pid.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Central black holeEdit

Research suggests the presence of a supermassive black hole in the center of this galaxy with a mass estimated to be 5 million times that of the Sun, which is slightly heavier than Sagittarius A*.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Distance estimatesEdit

At least two techniques have been used to measure distances to Sculptor in the past ten years.

Using the planetary nebula luminosity function method, an estimate of 10.89 Template:± million light years (or Mly; 3.34 Template:± Megaparsecs, or Mpc) was achieved in 2005.<ref name="Rekolaetal2005"> Template:Cite journal</ref>

The Sculptor Galaxy is close enough that the tip of the red-giant branch (TRGB) method may also be used to estimate its distance. The estimated distance to Sculptor using this technique in 2004 yielded Template:Val (Template:Val).<ref name="karachentsevetal2004">Template:Cite journal</ref><ref name="Karachentsevetal2006">Template:Cite journal</ref>

A weighted average of the most reliable distance estimates gives a distance of Template:Val (Template:Val).<ref name="Rekolaetal2005" />

SatelliteEdit

An international team of researchers has used the Subaru Telescope to identify a faint dwarf galaxy disrupted by NGC 253. The satellite galaxy is called NGC 253-dw2 and may not survive its next passage by its much larger host. The host galaxy may suffer some damage too if the dwarf is massive enough.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The interplay between the two galaxies is responsible for the disturbance in NGC 253's structure.<ref>Template:Cite journal</ref>