The Orion molecular cloud complex (or, simply, the Orion complex) is a star-forming region with stellar ages ranging up to 12 Myr. Two
giant molecular clouds are a part of it, Orion A and Orion B. The stars currently forming within the complex are located within these clouds. A number of other somewhat older stars no longer associated with the molecular gas are also part of the complex, most notably the
Orion's Belt
Orion's Belt or the Belt of Orion, also known as the Three Kings or Three Sisters, is an asterism in the constellation Orion. It consists of the three bright stars Alnitak
Alnitak is a triple star system in the constellation of ...
(Orion OB1b), as well as the dispersed population north of it (
Orion OB1a). Near the head of Orion there is also a population of young stars that is centered on
Meissa
Meissa , designated Lambda Orionis (λ Orionis, abbreviated Lambda Ori, λ Ori) is a star in the constellation of Orion. It is a multiple star approximately away with a combined apparent magnitude of 3.33. The main components are ...
. The complex is between 1 000 and 1 400 light-years away, and hundreds of light-years across.
The Orion complex is one of the most active regions of nearby
stellar formation visible in the night sky, and is home to both
protoplanetary discs
A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may also be considered an accretion disk for the star itself, be ...
and very young
star
A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
s. Much of it is bright in
infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
wavelengths due to the heat-intensive processes involved in stellar formation, though the complex contains
dark nebulae
A dark nebula or absorption nebula is a type of interstellar cloud, particularly molecular clouds, that is so dense that it obscures the visible wavelengths of light from objects behind it, such as background stars and emission or reflection nebu ...
,
emission nebulae,
reflection nebulae, and
H II 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. The presence of ripples on the surface of Orion's molecular clouds was discovered in 2010. The ripples are a result of the expansion of the nebulae gas over pre-existing molecular gas.
The Orion complex includes a large group of bright
nebula
A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regio ...
e,
dark clouds in the
Orion constellation. Several nebulae can be observed through
binoculars
Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...
and 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 observe ...
s, and some parts (such as the
Orion Nebula) are visible to the naked eye.
Nebulae within the complex
The following is a list of notable regions within the larger complex:
* Orion A molecular cloud
**The
Orion Nebula, also known as M42 (part of
Orion's Sword Orion's Sword is a compact asterism in the constellation Orion. It comprises three stars (42 Orionis, Theta Orionis, and Iota Orionis) and M42, the Orion Nebula, which together are thought to resemble a sword or its scabbard. This group is so ...
)
**
M43, which is part of the Orion Nebula
**
Sh2-279
Sh2-279 (alternatively designated S279 or Sharpless 279) is an HII region and bright nebulae that includes a reflection nebula located in the constellation Orion. It is the northernmost part of the asterism known as Orion's Sword, lying 0.6° n ...
(part of Orion's Sword)
**
NGC 1980
NGC 1980 (also known as OCL 529, Collinder 72 and The Lost Jewel of Orion) is a young open cluster associated with an emission nebula in the constellation Orion. It was discovered by William Herschel
Frederick William Herschel (; german: ...
(part of Orion's Sword)
**
Orion molecular cloud 1
Orion () may refer to:
Common meanings
* Orion (constellation), named after the mythical hunter
* Orion (mythology), a hunter in Greek mythology
* Orion (spacecraft), NASA crew vehicle first launched in 2022
Arts and media
Fictional en ...
(OMC-1) with the
Becklin–Neugebauer Object
The Becklin–Neugebauer Object (BN) is an object visible only in the infrared in the Orion molecular cloud 1 (OMC1). It was discovered in 1967 by Eric Becklin and Gerry Neugebauer during their near-infrared survey of the Orion Nebula. ...
and the
Kleinmann–Low Nebula
The Kleinmann–Low Nebula (also known as the Orion KL Nebula) is an active star forming region in the Milky Way galaxy. It is a cluster of stars within a molecular cloud.Ferland pp191
The Kleinmann–Low Nebula is at the heart of the Orion Ne ...
**
Orion molecular cloud 2
Orion () may refer to:
Common meanings
* Orion (constellation), named after the mythical hunter
* Orion (mythology), a hunter in Greek mythology
* Orion (spacecraft), NASA crew vehicle first launched in 2022
Arts and media
Fictional en ...
(OMC-2)
**
Orion molecular cloud 3
Orion () may refer to:
Common meanings
* Orion (constellation), named after the mythical hunter
* Orion (mythology), a hunter in Greek mythology
* Orion (spacecraft), NASA crew vehicle first launched in 2022
Arts and media
Fictional en ...
(OMC-3)
**
Orion molecular cloud 4
Orion () may refer to:
Common meanings
* Orion (constellation), named after the mythical hunter
* Orion (mythology), a hunter in Greek mythology
* Orion (spacecraft), NASA crew vehicle first launched in 2022
Arts and media
Fictional en ...
(OMC-4)
**
NGC 1981
NGC 1981 (also known as OCL 525) is an open cluster which is located in the constellation Orion. It was discovered by John Herschel on 4 January 1827. Its apparent magnitude is 4.2 and its size is 28.00 arc minutes. It lies to the north of t ...
**
NGC 1999
**
LDN 1641
**
HH 1/2, the first recognized
Herbig–Haro objects
**
HH 34 a Herbig–Haro object with symmetric
bow shock
In astrophysics, a bow shock occurs when the magnetosphere of an astrophysical object interacts with the nearby flowing ambient plasma such as the solar wind. For Earth and other magnetized planets, it is the boundary at which the speed of ...
s
* Orion B molecular cloud
**
Flame Nebula
__NOTOC__
The Flame Nebula, designated as NGC 2024 and Sh2-277, is an emission nebula in the constellation Orion. It is about 900 to 1,500 light-years away.
The bright star Alnitak (ζ Ori), the easternmost star in the Belt of Orion, shines en ...
(NGC 2024)
**
IC 434
IC 434 is a bright emission nebula in the constellation Orion. It was discovered on February 1, 1786 by William Herschel. The Horsehead Nebula is a dark nebula silhouetted against it.
See also
* Orion molecular cloud complex
The Orion mole ...
, which contains the Horsehead Nebula
** The
Horsehead Nebula
The Horsehead Nebula (also known as Barnard 33) is a small dark nebula in the constellation Orion. The nebula is located just to the south of Alnitak, the easternmost star of Orion's Belt, and is part of the much larger Orion molecular cloud co ...
(Barnard 33)
**
M78, a reflection nebula (NGC 2068)
**
McNeil's Nebula is a variable nebula discovered in 2004 near M78
** Orion East Cloud (LDN 1621 +
LDN 1622 LDN is usually contractional slang for London, UK.
LDN may also refer to: Arts and media
* London Daily News, former newspaper
* BBC London (formerly ''BBC LDN''), broadcasting body
* "LDN" (song), a 2006 single by Lily Allen
Language
* Láadan, ...
)
**
HH 24-26 this group contains three Herbig–Haro objects
**
HH 111
HH 111 is a Herbig-Haro object in the L1617 dark cloud of the Orion B molecular cloud in the constellation of Orion. It is a prototype of a highly collimated optical jet sources. It shows several bow shocks and has a length of about 2.6 light ...
one of the most well-known Herbig–Haro objects
*
Orion OB1 association
**
Orion's Belt
Orion's Belt or the Belt of Orion, also known as the Three Kings or Three Sisters, is an asterism in the constellation Orion. It consists of the three bright stars Alnitak
Alnitak is a triple star system in the constellation of ...
**
Sigma Ori cluster
**
25 Ori cluster
* Lambda Orionis molecular ring (
Sh2-264)
**
Lambda Ori cluster
**
Barnard 30
**
Barnard 35
*
Orion-Eridanus superbubble
**
Barnard's Loop
Barnard's Loop (catalogue designation Sh 2-276) is an emission nebula in the constellation of Orion. It is part of the Orion molecular cloud complex which also contains the dark Horsehead and bright Orion nebulae. The loop takes the form of ...
(Sh2-276)
**
Eridanus Loop Eridanus can refer to:
Rivers
*Eridanos (mythology) (or Eridanus), a river in Greek mythology, somewhere in Central Europe, which was territory that Ancient Greeks knew only vaguely
*The Po River, according to Roman word usage
*Eridanos (Athens), ...
A more complete list can be found for example in Maddalena et al. (1986) Table 1
Individual components
Orion A
The giant molecular cloud Orion A is the most active
star-forming region in the local neighbourhood of the Sun. In the last few million years about 3000
young stellar object
Young stellar object (YSO) denotes a star in its early stage of evolution. This class consists of two groups of objects: protostars and pre-main-sequence stars.
Classification by spectral energy distribution
A star forms by accumulation of mate ...
s were formed in this region, including about 190
protostar
A protostar is a very young star that is still gathering mass from its parent molecular cloud. The protostellar phase is the earliest one in the process of stellar evolution. For a low-mass star (i.e. that of the Sun or lower), it lasts about 5 ...
s and about 2600
pre-main sequence stars. The Orion A cloud has a mass in the order of 10
5 .
The stars in Orion A do not have the same distance to us. The "head" of the cloud, which also contains the
Orion Nebula is about 1300
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 (400
parsecs
The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, an ...
) away from the Sun. The "tail" however is up to 1530 light-years (470 parsecs) away from the Sun. The Orion A cloud is therefore longer than the projected length of 130 light-years (40 parsecs) and has a true length of 290 light-years (90 parsecs).
Orion Molecular Clouds
The
Orion Molecular Clouds (OMC 1 to OMC 4) are molecular clouds located behind the Orion Nebula. Most of the light from the OMCs are blocked by material from the Orion Nebula, but some features like the
Kleinmann-Low Nebula and the
Becklin-Neugebauer object can be seen in the infrared. The clouds can be seen in the
far-infrared
Far infrared (FIR) is a region in the infrared spectrum of electromagnetic radiation. Far infrared is often defined as any radiation with a wavelength of 15 micrometers (μm) to 1 mm (corresponding to a range of about 20 THz to ...
and in
radio
Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmit ...
wavelengths. The
Trapezium Cluster
The Trapezium or Orion Trapezium Cluster, also known by its Bayer designation of Theta1 Orionis, is a tight open cluster of stars in the heart of the Orion Nebula, in the constellation of Orion. It was discovered by Galileo Galilei. On 4 F ...
has a small angular separation from the Kleinmann-Low Nebula, but the Trapezium Cluster is located inside the Orion Nebula, which is closer towards earth.
Orion B
Orion B is about 1370 light-years (420 parsecs) from Earth. It has a size of about 1.5 kpc² and a mass in the order of 10
5 . It contains several star forming regions with the star cluster inside the
Flame Nebula
__NOTOC__
The Flame Nebula, designated as NGC 2024 and Sh2-277, is an emission nebula in the constellation Orion. It is about 900 to 1,500 light-years away.
The bright star Alnitak (ζ Ori), the easternmost star in the Belt of Orion, shines en ...
being the largest cluster.
Orion OB1 association
The Orion OB1 association represents different stellar populations that are superimposed along our line of sight. The oldest group with 8-10 million years is Orion OB1a, northwest of
Orion's Belt
Orion's Belt or the Belt of Orion, also known as the Three Kings or Three Sisters, is an asterism in the constellation Orion. It consists of the three bright stars Alnitak
Alnitak is a triple star system in the constellation of ...
, and the youngest group with less than 2 million years is Orion OB1d, which contains the
Orion Nebula cluster and
NGC 2024.
Lambda Orionis molecular ring
The Lambda Orionis ring is a large molecular ring, centered around Lambda Orioinis (
Meissa
Meissa , designated Lambda Orionis (λ Orionis, abbreviated Lambda Ori, λ Ori) is a star in the constellation of Orion. It is a multiple star approximately away with a combined apparent magnitude of 3.33. The main components are ...
). It was suggested that this ring formed after a
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 ...
occurred inside the central
star-forming region that once surrounded the
Lambda Orionis Cluster, dispersing the material into the ring seen today. Star-formation is still continuing in regions of the ring.
Superbubble
Parts of the Orion-Eridanus
superbubble were first seen as
Barnard's Loop
Barnard's Loop (catalogue designation Sh 2-276) is an emission nebula in the constellation of Orion. It is part of the Orion molecular cloud complex which also contains the dark Horsehead and bright Orion nebulae. The loop takes the form of ...
in
Hydrogen-alpha images that warp around the eastern portion of Orion. The other part of the superbubble that is seen in H-alpha is the
Eridanus Loop Eridanus can refer to:
Rivers
*Eridanos (mythology) (or Eridanus), a river in Greek mythology, somewhere in Central Europe, which was territory that Ancient Greeks knew only vaguely
*The Po River, according to Roman word usage
*Eridanos (Athens), ...
. The walls of the entire bubble are seen in far-infrared and HI. Some features of the Eridanus Loop might be as close as 590 light-years (180 parsecs) to the sun.
Gallery
File:Orion-Constellation.jpg, Orion from Leh
Leh () ( lbj, ) is the joint capital and largest city of Ladakh, a union territory of India. Leh, located in the Leh district, was also the historical capital of the Kingdom of Ladakh, the seat of which was in the Leh Palace, the former res ...
with the molecular clouds visible.
File:Sword of Orion, Orion nebula - Herschel - Nhsc2016-003b.tif, Orion A seen by ESA's Herschel Space Observatory
The Herschel Space Observatory was a space observatory built and operated by the European Space Agency (ESA). It was active from 2009 to 2013, and was the largest infrared telescope ever launched until the launch of the James Webb Space Telesc ...
File:Herschel’s view of a molecular cloud ESA384010.jpg, Orion B seen by ESA's Herschel Space Observatory
The Herschel Space Observatory was a space observatory built and operated by the European Space Agency (ESA). It was active from 2009 to 2013, and was the largest infrared telescope ever launched until the launch of the James Webb Space Telesc ...
File:Orion's Big Head Revealed in Infrared.jpg, The Lambda Orionis ring seen by NASA's Wide-field Infrared Survey Explorer
Wide-field Infrared Survey Explorer (WISE, observatory code C51, Explorer 92 and SMEX-6) is a NASA infrared astronomy space telescope in the Explorers Program. It was launched in December 2009, and placed in hibernation mode in February 2011, ...
File:BarnardLoopHunterWilson.jpg, H-alpha image of Barnard's Loop
Barnard's Loop (catalogue designation Sh 2-276) is an emission nebula in the constellation of Orion. It is part of the Orion molecular cloud complex which also contains the dark Horsehead and bright Orion nebulae. The loop takes the form of ...
, which is part of the Orion–Eridanus Superbubble
File:Hubble Sees the Force Awakening in a Newborn Star (23807356641).jpg, The Herbig–Haro object HH 24, which is located in Orion B
File:Infant_Stars_in_Orion_-_chaotic_birth_of_stars.jpg, These four images taken by the NASA/ESA Hubble Space Telescope reveal the chaotic birth of stars in the Orion complex, the nearest major star-forming region to Earth.
See also
*
Runaway star
In astronomy, stellar kinematics is the Observational astronomy, observational study or measurement of the kinematics or motions of stars through space.
Stellar kinematics encompasses the measurement of stellar Velocity, velocities in the Milky W ...
*
Rho Ophiuchi cloud complex
The Rho Ophiuchi cloud complex is a complex of interstellar clouds with different nebulae, particularly dark nebulae which is centered 1° south of the star ρ Ophiuchi, which it among others extends to, of the constellation Ophiuchus. At an es ...
*
Taurus molecular cloud
*
Perseus molecular cloud
The Perseus molecular cloud (Per MCld) is a nearby (~1000 ly) giant molecular cloud in the constellation of Perseus and contains over 10,000 solar masses of gas and dust covering an area of 6 by 2 degrees. Unlike the Orion molecular cloud it is a ...
*
Scorpius–Centaurus association
References
{{Reflist
External links
Orion Cloud ComplexESO: Hidden Secrets of Orion’s Cloudsincl. Photos & Animations
Orion (constellation)
Molecular clouds