The Keyhole, or Keyhole Nebula, is a small dark cloud of cold molecules and dust within the Carina Nebula, containing bright filaments of hot, fluorescing gas, silhouetted against the much brighter background nebula. John Herschel used the term "lemniscate-oval vacuity" when first describing it,and subsequently referred to it simply as the "oval vacuity".The term lemniscate continued to be used to describe this portion of the nebula until popular astronomy writer Emma Converse described the shape of the nebula as "resembling a keyhole" in an 1873 Appleton's Journal article.The name Keyhole Nebula then came into common use, sometimes for the Keyhole itself, sometimes to describe the whole of the Carina Nebula (signifying "the nebula that contains the Keyhole").

The diameter of the Keyhole structure is approximately seven light-years (2.1 pc). Its appearance has changed significantly since it was first observed, possibly due to changes in the ionizing radiation from Eta Carinae. The Keyhole does not have its own NGC designation. It is sometimes erroneously called NGC 3324,but that catalogue designation refers to a reflection and emission nebula just northwest of the Carina Nebula (or to its embedded star cluster).The Carina Nebula or Eta Carinae Nebula(catalogued as NGC 3372; also known as the Great Carina Nebula=10.5px ) is a large, complex area of bright and dark nebulosity in the constellation Carina, located in the Carina–Sagittarius Arm of the Milky Way galaxy. The nebula is approximately 8,500 light-years (2,600 pc) from Earth.The nebula has within its boundaries the large Carina OB1association and several related open clusters, including numerous O-type stars and several Wolf–Rayet stars. Carina OB1 encompasses the star clustersTrumpler 14 and Trumpler 16. Trumpler 14 is one of the youngest known star clusters at half a million years old and contains stars like the O2 supergiant HD 93129A. Trumpler 16 is the home of many extremely luminous stars, such as WR 25 and the Eta Carinae star system. Trumpler 15, Collinder 228, Collinder 232, NGC 3324, and NGC 3293 are also considered members of the association. NGC 3293 is the oldest and furthest from Trumpler 14, indicating sequential and ongoing star formation.The nebula is one of the largest diffuse nebulae in our skies. Although it is four times as large as and even brighter than the famous Orion Nebula, the Carina Nebula is much less well known due to its location in the southern sky. It was discovered by Nicolas-Louis de Lacaille in 1752 from the Cape of Good Hope.The Carina Nebula was selected as one of five cosmic objects observed by the James Webb Space Telescope, as part of the release of its first official science images. A detailed image was made of an early star-forming region of NGC 3324 known as the Cosmic Cliffs.

Nicolas-Louis de Lacaille discovered the nebula on 25 January 1752. Its dimensions are 120×120 arcminutes centered on the coordinates of right ascension 10h 45m 08.5s and declination −59° 52′ 04″.In modern times it is calculated to be around 8,500 light-years (2,600 pc) from Earth.
 Eta Carinae is a highly luminoushypergiantstar. Estimates of its mass range from 100 to 150 times the mass of the Sun, and its luminosity is about four million times that of the Sun.This object is currently the most massive star that can be studied in great detail, because of its location and size. Several other known stars may be more luminous and more massive, but data on them is far less robust. (Caveat: Since examples such as the Pistol Star have been demoted by improved data, one should be skeptical of most available lists of "most massive stars". In 2006, Eta Carinae still had the highest confirmed luminosity, based on data across a broad range of wavelengths.) Stars with more than 80 times the mass of the Sun produce more than a million times as much light as the Sun. They are quite rare—only a few dozen in a galaxy as big as ours—and they flirt with disaster near the Eddington limit, i.e., the outward pressure of their radiation is almost strong enough to counteract gravity. Stars that are more than 120 solar masses exceed the theoretical Eddington limit, and their gravity is barely strong enough to hold in its radiation and gas, resulting in a possible supernova or hypernova in the near future.Eta Carinae's effects on the nebula can be seen directly. Dark globules and some other less visible objects have tails pointing directly away from the massive star. The entire nebula would have looked very different before the Great Eruption in the 1840s surrounded Eta Carinae with dust, drastically reducing the amount of ultraviolet light it put into the nebula.

Defiant Finger

A small Bok globule in the Keyhole Nebula (at RA 10h 44m 30s, Dec −59° 40') has been photographed by the Hubble Space Telescope and is nicknamed the "Carina Defiant Finger" due to its shape. In Hubble images, light can be seen radiating off the edges of the globule; this is especially visible in the southern tip, where the "finger" is. It is thought that the Defiant Finger is being ionized by the bright Wolf–Rayet star WR 25, and/or Trumpler 16-244, a bright blue supergiant. It has a mass of at least 6 M☉, and stars may be forming within it. Like other interstellar clouds under intense radiation, the Defiant Finger will eventually be completely evaporated; for this cloud the time frame is predicted to be 200,000 to 1,000,000 years.




Annotated map