NGC 6118 is a

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

located 83 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 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 ...

Serpens Serpens ( grc, , , the Serpent) is a constellation in the northern celestial hemisphere. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy, it remains one of the 88 modern constellations designated by the International ...

(the Snake). It measures roughly 110,000 light-years across; about the same as our own

galaxy A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System ...

, the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

. Its shape is classified as " SA(s)cd," meaning that it is unbarred and has several rather loosely wound spiral arms. The large numbers of bright bluish knots are active star-forming regions where some very luminous and young stars can be perceived. Because NGC 6118 has loosely wound spiral open arms, no clear defined spiral arms like the

galaxy and lacks a central bar, the galaxy thus does not have a

galactic habitable zone In astrobiology and planetary astrophysics, the galactic habitable zone is the region of a galaxy in which life might most likely develop. The concept of a galactic habitable zone analyzes various factors, such as metallicity (the presence of elem ...

like the Milky Way. For the Milky Way, the galactic habitable zone is commonly believed to be an

annulus Annulus (or anulus) or annular indicates a ring- or donut-shaped area or structure. It may refer to: Human anatomy * ''Anulus fibrosus disci intervertebralis'', spinal structure * Annulus of Zinn, a.k.a. annular tendon or ''anulus tendineus com ...

with an outer radius of about 10 kiloparsecs and an inner radius close to the

Galactic Center The Galactic Center or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact ra ...

, both of which lack hard boundaries. NGC 6118 is difficult to see with a small

telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to obse ...

. Amateur astronomers have nicknamed it the "Blinking Galaxy", as it has a tendency to flick in and out of view with different eye positions.

Supernova 2004dk

SN 2004dk was first reported by James Graham and Weidong Li on 1 August 2004. They found the new

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 ...

by studying images produced by the

Lick Observatory Supernova Search The Lick Observatory is an astronomical observatory owned and operated by the University of California. It is on the summit of Mount Hamilton, in the Diablo Range just east of San Jose, California, United States. The observatory is managed by th ...

(LOSS) program with the 76 cm

Katzman Automatic Imaging Telescope The Katzman Automatic Imaging Telescope (KAIT) is an automated telescope used in the search for supernovae. The telescope had a first light in 1998, and is a noted robotic telescope. It had first recorded data in August 1996, and was formally ded ...

(KAIT) in San Jose, CA. SN 2004dk was initially classified by

European Southern Observatory The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental research organisation made up of 16 member states for ground-based ast ...

astronomer Fernando Patat et al. on 4 Aug 2004 as a Type Ic supernova.

Type Ib and Ic supernovae Type Ib and Type Ic supernovae are categories of supernovae that are caused by the stellar core collapse of massive stars. These stars have shed or been stripped of their outer envelope of hydrogen, and, when compared to the spectr ...

are the end result of massive stars (> 8 solar masses) that have run out of

nuclear fuel Nuclear fuel is material used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission. Most nuclear fuels contain heavy fissile actinide elements that are capable of undergo ...

. Normally one would expect to see evidence of hydrogen and helium, but when these supernova occur in a

binary system A binary system is a system of two astronomical bodies which are close enough that their gravitational attraction causes them to orbit each other around a barycenter ''(also see animated examples)''. More restrictive definitions require that th ...

the companion has sometimes

gravitation In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stron ...

ally stripped the outer layers of the progenitor star away, leaving only the heavier elements. Type Ib supernovae have no hydrogen, while Type Ics have neither hydrogen or helium. Over the following weeks

Alexei Filippenko Alexei Vladimir "Alex" Filippenko (; born July 25, 1958) is an American astrophysicist and professor of astronomy at the University of California, Berkeley. Filippenko graduated from Dos Pueblos High School in Goleta, California. He received a ...

et al. and the

University of California at Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public university, public land-grant university, land-grant research university in Berkeley, California. Established in 1868 as the University of Californi ...

discovered prominent He I absorption lines, thus changing the classification of the supernova to Type Ib.

References

External links

* {{DEFAULTSORT:NGC 6118 Unbarred spiral galaxies Serpens (constellation) 6118 057924