Great Orion Nebula
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The Orion Nebula (also known as Messier 42, M42, or NGC 1976) is a diffuse nebula in the
Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...
situated south of
Orion's Belt Orion's Belt is an asterism in the constellation of Orion. Other names include the Belt of Orion, the Three Kings, and the Three Sisters. The belt consists of three bright and easily identifiable collinear star systems – Alnitak, Alnilam, ...
in the constellation of Orion, and is known as the middle "star" in the "sword" of Orion. It is one of the brightest
nebula A nebula (; 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 regions, such as in the Pillars of Creation in ...
e and is visible to the
naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...
in the night sky with an
apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...
of 4.0. It is away and is the closest region of massive
star formation Star formation is the process by which dense regions within molecular clouds in interstellar space—sometimes referred to as "stellar nurseries" or "star-forming regions"—Jeans instability, collapse and form stars. As a branch of astronomy, sta ...
to
Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
. M42 is estimated to be 25 light-years across (so its apparent size from Earth is approximately 1 degree). It has a mass of about 2,000 times that of the
Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
. Older texts frequently refer to the Orion Nebula as the Great Nebula in Orion or the Great Orion Nebula. The Orion Nebula is one of the most scrutinized and photographed objects in the night sky and is among the most intensely studied celestial features.Press release,
Astronomers Spot The Great Orion Nebula's Successor
", Harvard-Smithsonian Center for Astrophysics, 2006.
The nebula has revealed much about the process of how
star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
s and
planet A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...
ary systems are formed from collapsing clouds of gas and dust. Astronomers have directly observed
protoplanetary disk 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 not be considered an accretion disk; while the two are sim ...
s and
brown dwarf Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...
s within the nebula, intense and turbulent motions of the gas, and the photo-ionizing effects of massive nearby stars in the nebula.


Physical characteristics

The Orion Nebula is visible with the naked eye even from areas affected by
light pollution Light pollution is the presence of any unwanted, inappropriate, or excessive artificial Visible spectrum, lighting. In a descriptive sense, the term ''light pollution'' refers to the effects of any poorly implemented lighting sources, during the ...
. It is seen as the middle "star" in the "sword" of Orion, which are the three stars located south of Orion's Belt. The "star" appears fuzzy to sharp-eyed observers, and the nebulosity is obvious 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 ...
or a small
telescope A telescope is a device used to observe distant objects by their emission, Absorption (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using len ...
. The peak surface brightness of the central region of M42 is about 17 Mag/arcsec2 and the outer bluish glow has a peak surface brightness of 21.3 Mag/arcsec2. The Orion Nebula contains a very young
open cluster An open cluster is a type of star cluster made of tens to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...
, known as the
Trapezium Cluster The Trapezium or Orion Trapezium Cluster, also known by its Bayer designation of Theta1 Orionis (θ1 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 Galile ...
due to the asterism of its primary four stars within a diameter of 1.5 light years. Two of these can be resolved into their component binary systems on nights with good seeing, giving a total of six stars. The stars of the Trapezium Cluster, along with many other stars, are still in their early years. The Trapezium Cluster is a component of the much larger Orion Nebula cluster, an association of about 2,800 stars within a diameter of 20 light years. The Orion Nebula is in turn surrounded by the much larger
Orion molecular cloud complex The Orion molecular cloud complex (or, simply, the Orion complex) is a star-forming region with stellar ages ranging up to 12 Myr. Two Molecular cloud#Giant molecular clouds, giant molecular clouds are a part of it, Orion A and Orion B. The stars ...
, which is hundreds of light years across, spanning the whole Orion Constellation. Two million years ago the Orion Nebula cluster may have been the home of the
runaway star In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as ...
s
AE Aurigae AE Aurigae (abbreviated as AE Aur) is a runaway star in the constellation Auriga; it lights the Flaming Star Nebula. Description AE Aurigae is a blue O-type main sequence star with a mean apparent magnitude of +6.0, making it faint ...
,
53 Arietis 53 Arietis (abbreviated 53 Ari) is a variable star in the northern constellation of Aries. ''53 Arietis'' is the Flamsteed designation; it also bears the variable star designation UW Arietis. It is a B-type main sequence star with a s ...
, and
Mu Columbae Mu Columbae (μ Col, μ Columbae) is a star in the constellation of Columba. It is one of the few O-class stars that are visible to the unaided eye. The star is known to lie approximately 1,900 light years from the Solar System (with an e ...
, which are currently moving away from the nebula at speeds greater than .


Coloration

Observers have long noted a distinctive greenish tint to the nebula, in addition to regions of red and of blue-violet. The red hue is a result of the recombination line
radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes: * ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infr ...
at a
wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
of 656.3  nm. The blue-violet coloration is the reflected radiation from the massive O-class stars at the core of the nebula. The green hue was a puzzle for astronomers in the early part of the 20th century because none of the known
spectral line A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission (electromagnetic radiation), emission or absorption (electromagnetic radiation), absorption of light in a narrow frequency ...
s at that time could explain it. There was some speculation that the lines were caused by a new element, and the name
nebulium Nebulium was a proposed chemical element, element found in astronomical observation of a nebula by William Huggins in 1864. The strong green emission spectrum, emission lines of the Cat's Eye Nebula, discovered using spectroscopy, led to the post ...
was coined for this mysterious material. With better understanding of
atomic physics Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. Atomic physics typically refers to the study of atomic structure and the interaction between atoms. It is primarily concerned wit ...
, however, it was later determined that the green spectrum was caused by a low-probability
electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...
transition in
doubly ionized oxygen In astronomy and atomic physics, doubly ionized oxygen is the ion O2+ (O III in spectroscopic notation). Ion Its emission forbidden lines in the visible spectrum fall primarily at the wavelength 500.7 nm, and secondarily at 495.9 n ...
, a so-called "
forbidden transition In spectroscopy, a forbidden mechanism (forbidden transition or forbidden line) is a spectral line associated with absorption or emission of photons by atomic nuclei, atoms, or molecules which undergo a transition that is not allowed by a particu ...
". This radiation was impossible to reproduce in the laboratory at the time, because it depended on the quiescent and nearly collision-free environment found in the high vacuum of deep space.


History

There has been speculation that the
Mayans Maya () are an ethnolinguistic group of Indigenous peoples of the Americas, Indigenous peoples of Mesoamerica. The ancient Maya civilization was formed by members of this group, and today's Maya are generally descended from people who lived w ...
of
Central America Central America is a subregion of North America. Its political boundaries are defined as bordering Mexico to the north, Colombia to the southeast, the Caribbean to the east, and the Pacific Ocean to the southwest. Central America is usually ...
may have described the nebula within their "Three Hearthstones" creation myth; if so, the three would correspond to two stars at the base of Orion,
Rigel Rigel is a blue supergiant star in the constellation of Orion. It has the Bayer designation β Orionis, which is Latinized to Beta Orionis and abbreviated Beta Ori or β Ori. Rigel is the brightest and most massive componentand ...
and
Saiph Saiph , designation Kappa Orionis (κ Orionis, abbreviated Kappa Ori, κ Ori) and 53 Orionis (53 Ori), is a blue supergiant star and the sixth-brightest star in the constellation of Orion. Of the four bright stars that compose Orion's mai ...
, and another,
Alnitak Alnitak is a triple star system in the constellation of Orion. It has the designations ζ Orionis, which is Latinised to Zeta Orionis and abbreviated Zeta Ori or ζ Ori, and 50 Orionis, abbreviated 50 Ori. The system is located at a ...
at the southern (left) tip of the "hunter's belt", which together form the vertices of a nearly perfect equilateral triangle, the same shape as traditional Mayan
hearths A hearth () is the place in a home where a fire is or was traditionally kept for home heating and for cooking, usually constituted by a horizontal hearthstone and often enclosed to varying degrees by any combination of reredos (a low, partial ...
. Near the center of the triangle is Orion's Sword (including the Orion Nebula), which ancient Mayan mythology regarded as the literal or figurative embers of a fiery creation smoldering at the center of the hearth. Similarly, modern Lacandon Maya regard it as smoke from
copal Copal is a tree resin, particularly the aromatic resins from the copal tree '' Protium copal'' ( Burseraceae) used by the cultures of pre-Columbian Mesoamerica as ceremonially burned incense and for other purposes. More generally, copal includ ...
incense. Neither
Ptolemy Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...
's ''
Almagest The ''Almagest'' ( ) is a 2nd-century Greek mathematics, mathematical and Greek astronomy, astronomical treatise on the apparent motions of the stars and planetary paths, written by Ptolemy, Claudius Ptolemy ( ) in Koine Greek. One of the most i ...
'' nor
al Sufi ʿAbd al-Raḥmān al-Ṣūfī (; 7 December 90325 May 986) was a Persian astronomer. His work '' '' ("''The Book of Fixed Stars''"), written in 964, included both textual descriptions and illustrations. The Persian polymath Al-Biruni wrote tha ...
's ''
Book of Fixed Stars ''The Book of Fixed Stars'' ( ', literally ''The Book of the Shapes of Stars'') is an Astronomy, astronomical text written by Abd al-Rahman al-Sufi (Azophi) around 964. Following Graeco-Arabic translation movement, the translation movement in the ...
'' noted this nebula, even though they both listed patches of nebulosity elsewhere in the night sky; nor did
Galileo Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642), commonly referred to as Galileo Galilei ( , , ) or mononymously as Galileo, was an Italian astronomer, physicist and engineer, sometimes described as a poly ...
mention it, even though he also made telescopic observations surrounding it in 1610 and 1617. This has led to some speculation that a flare-up of the illuminating stars may have increased the brightness of the nebula. The first discovery of the diffuse nebulous nature of the Orion Nebula is generally credited to French astronomer
Nicolas-Claude Fabri de Peiresc Nicolas-Claude Fabri de Peiresc (1 December 1580 – 24 June 1637), often known simply as Peiresc, or by the Latin form of his name, Peirescius, was a French astronomer, antiquary and savant, who maintained a wide correspondence with scienti ...
, on November 26, 1610, when he recorded observing it with a
refracting telescope A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens (optics), lens as its objective (optics), objective to form an image (also referred to a dioptrics, dioptric telescope). The refracting telescope d ...
purchased by his patron
Guillaume du Vair Guillaume du Vair (7 March 1556 – 3 August 1621) was a French bishop, author, lawyer, Magistrate of the Parliament and Keeper of the Seals of France under French king Louis XIII. Life Du Vair was born in Paris. After taking holy orders, he ex ...
. The first published observation of the nebula was by the Jesuit mathematician and astronomer Johann Baptist Cysat of
Lucerne Lucerne ( ) or Luzern ()Other languages: ; ; ; . is a city in central Switzerland, in the Languages of Switzerland, German-speaking portion of the country. Lucerne is the capital of the canton of Lucerne and part of the Lucerne (district), di ...
in his 1619 monograph on the comets (describing observations of the nebula that may date back to 1611). He made comparisons between it and a bright
comet A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or Coma (cometary), coma surrounding ...
seen in 1618, describing how the nebula appeared through his telescope: His description of the center stars as different from a comet's head in that they were a "rectangle" may have been an early description of the
Trapezium Cluster The Trapezium or Orion Trapezium Cluster, also known by its Bayer designation of Theta1 Orionis (θ1 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 Galile ...
. (The first detection of three of the four stars of this cluster is credited to
Galileo Galilei Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642), commonly referred to as Galileo Galilei ( , , ) or mononymously as Galileo, was an Italian astronomer, physicist and engineer, sometimes described as a poly ...
on February 4, 1617. ) The nebula was independently "discovered" (though visible to the naked eye) by several other prominent astronomers in the following years, including by
Giovanni Battista Hodierna Giovanni Battista Hodierna, also spelled as Odierna (April 13, 1597 – April 6, 1660) was an Italian astronomer at the court of Giulio Tomasi, Duke of Palma (Palma di Montechiaro). He compiled a catalogue of comets and other celestial object ...
(whose sketch was the first published in ''
De systemate orbis cometici, deque admirandis coeli characteribus ''De systemate orbis cometici, deque admirandis coeli characteribus'' (transl. ''Of the systematics of the world of comets, and on the admirable objects of the sky'') is a small tract (literature), tract on comets and other celestial objects by th ...
''). In 1659, Dutch scientist
Christiaan Huygens Christiaan Huygens, Halen, Lord of Zeelhem, ( , ; ; also spelled Huyghens; ; 14 April 1629 – 8 July 1695) was a Dutch mathematician, physicist, engineer, astronomer, and inventor who is regarded as a key figure in the Scientific Revolution ...
published the first detailed drawing of the central region of the nebula in ''Systema Saturnium''.
Charles Messier Charles Messier (; 26 June 1730 – 12 April 1817) was a French astronomer. He published an astronomical catalogue consisting of 110 nebulae and star clusters, which came to be known as the ''Messier objects'', referred to with th ...
observed the nebula on March 4, 1769, and he also noted three of the stars in Trapezium. Messier published the first edition of his catalog of deep sky objects in 1774 (completed in 1771). As the Orion Nebula was the 42nd object in his list, it became identified as M42.
John Herschel Sir John Frederick William Herschel, 1st Baronet (; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor and experimental photographer who invented the blueprint and did botanical work. ...
conducted the first survey of the nebula as seen from the southern hemisphere in the period between 1834 to 1838. The Orion Nebula was observed and charted as part of Herschel's survey of the whole surface of the visible heavens starting in 1825, the southern hemisphere observations conducted from a private 21 ft (6.4 m) telescope in what is today
Cape Town, South Africa Cape Town is the legislature, legislative capital city, capital of South Africa. It is the country's oldest city and the seat of the Parliament of South Africa. Cape Town is the country's List of municipalities in South Africa, second-largest ...
. In 1865, English
amateur astronomer Amateur astronomy is a hobby where participants enjoy observing or imaging celestial objects in the sky using the unaided eye, binoculars, or telescopes. Even though scientific research may not be their primary goal, some amateur astronomers m ...
William Huggins Sir William Huggins (7 February 1824 – 12 May 1910) was a British astronomer best known for his pioneering work in astronomical spectroscopy together with his wife, Margaret. Biography William Huggins was born at Cornhill, Middlesex, in 1 ...
used his visual
spectroscopy Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectro ...
method to examine the nebula, showing that it, like other nebulae he had examined, was made up of "luminous gas". On September 30, 1880,
Henry Draper Henry Draper (March 7, 1837 – November 20, 1882) was an American medical doctor and amateur astronomer. He is best known today as a pioneer of astrophotography. Life and work Henry Draper's father, John William Draper, was an accomplished do ...
used the new
dry plate The gelatin silver print is the most commonly used chemical process in black-and-white photography, and is the fundamental chemical process for modern analog color photography. As such, films and printing papers available for analog photography r ...
photographic process with an
refracting telescope A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens (optics), lens as its objective (optics), objective to form an image (also referred to a dioptrics, dioptric telescope). The refracting telescope d ...
to make a 51-minute exposure of the Orion Nebula, the first instance of
astrophotography Astrophotography, also known as astronomical imaging, is the photography or imaging of astronomical objects, celestial events, or areas of the night sky. The first photograph of an astronomical object (the Moon) was taken in 1839, but it was no ...
of a nebula in history. Another breakthrough in astronomical photography occurred in 1883, when amateur astronomer
Andrew Ainslie Common Andrew Ainslie Common Fellow of the Royal Society, FRS (1841–1903) was an English amateur astronomer best known for his pioneering work in astrophotography. Biography Common was born in Newcastle Upon Tyne on 7 August 1841. His father, Thomas ...
used the dry plate process to record several images in exposures up to 60 minutes with a
reflecting telescope A reflecting telescope (also called a reflector) is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century by Isaac Newton as an alternati ...
that he constructed in the backyard of his home in
Ealing Ealing () is a district in west London (sub-region), west London, England, west of Charing Cross in the London Borough of Ealing. It is the administrative centre of the borough and is identified as a major metropolitan centre in the London Pl ...
, west London. These images, for the first time, showed stars and nebula detail too faint to be seen by the human eye. In 1902, Vogel and Eberhard discovered differing velocities within the nebula, and by 1914 astronomers at
Marseille Marseille (; ; see #Name, below) is a city in southern France, the Prefectures in France, prefecture of the Departments of France, department of Bouches-du-Rhône and of the Provence-Alpes-Côte d'Azur Regions of France, region. Situated in the ...
had used the interferometer to detect rotation and irregular motions. Campbell and Moore confirmed these results using the spectrograph, demonstrating turbulence within the nebula. In 1931, Robert J. Trumpler noted that the fainter stars near the Trapezium formed a cluster, and he was the first to name them the "
Trapezium Cluster The Trapezium or Orion Trapezium Cluster, also known by its Bayer designation of Theta1 Orionis (θ1 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 Galile ...
". Based on their magnitudes and spectral types, he derived a distance estimate of 1,800 light years. This was three times farther than the commonly accepted distance estimate of the period but was much closer to the modern value. In 1993, the
Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...
(HST) first observed the Orion Nebula. Since then, the nebula has been a frequent target for HST studies. The images have been used to build a detailed model of the nebula in three dimensions.
Protoplanetary disk 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 not be considered an accretion disk; while the two are sim ...
s have been observed around most of the newly formed stars in the nebula, and the destructive effects of high levels of
ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...
energy from the most massive stars have been studied. In 2005, the ''Advanced Camera for Surveys'' instrument of the Hubble Space Telescope finished capturing the most detailed image of the nebula yet taken. The image was taken through 104 orbits of the telescope, capturing over 3,000 stars down to the 23rd magnitude, including infant
brown dwarf Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...
s and possible brown dwarf
binary star A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...
s. A year later, scientists working with the HST announced the first ever masses of a pair of eclipsing binary brown dwarfs, 2MASS J05352184–0546085. The pair are located in the Orion Nebula and have approximate masses of and respectively, with an orbital period of 9.8 days. Surprisingly, the more massive of the two also turned out to be the less luminous. In October 2023, astronomers, based on observations of the Orion Nebula with the
James Webb Space Telescope The James Webb Space Telescope (JWST) is a space telescope designed to conduct infrared astronomy. As the largest telescope in space, it is equipped with high-resolution and high-sensitivity instruments, allowing it to view objects too old, Lis ...
, reported the discovery of ''pairs'' of
rogue planet A rogue planet, also termed a free-floating planet (FFP) or an isolated planetary-mass object (iPMO), is an interstellar object of planetary mass which is not gravitationally bound to any star or brown dwarf. Rogue planets may originate from ...
s, similar in mass to the planet
Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...
, and called JuMBOs (Jupiter Mass Binary Objects).


Structure

The entirety of the Orion Nebula extends across a 1° region of the sky, and includes neutral clouds of gas and dust, associations of stars, ionized volumes of gas, and
reflection nebula In astronomy, reflection nebulae are interstellar cloud, clouds of Cosmic dust, interstellar dust which might reflect the light of a nearby star or stars. The energy from the nearby stars is insufficient to Ionization, ionize the gas of the nebu ...
e. The Orion Nebula is part of a much larger nebula known as the
Orion molecular cloud complex The Orion molecular cloud complex (or, simply, the Orion complex) is a star-forming region with stellar ages ranging up to 12 Myr. Two Molecular cloud#Giant molecular clouds, giant molecular clouds are a part of it, Orion A and Orion B. The stars ...
, which extends throughout the constellation of Orion and includes
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 o ...
, the Horsehead Nebula, M43, M78, and the
Flame Nebula __NOTOC__ The Flame Nebula, designated as NGC 2024 and Sh2-277, is an emission nebula in the constellation Orion (constellation), Orion. It is about 1350 light-years away. At that distance, the Flame Nebula lies within the Orion B cloud of the la ...
. Stars are forming throughout the entire Cloud Complex, but most of the young stars are concentrated in dense clusters like the one illuminating the Orion Nebula. The current astronomical model for the nebula consists of an ionized ( H II) region, roughly centered on Theta1 Orionis C, which lies on the side of an elongated molecular cloud in a cavity formed by the massive young stars. (Theta1 Orionis C emits 3-4 times as much photoionizing light as the next brightest star, Theta2 Orionis A.) The H II region has a temperature ranging up to 10,000 K, but this temperature falls dramatically near the edge of the nebula. The nebulous emission comes primarily from photoionized gas on the back surface of the cavity. The H II region is surrounded by an irregular, concave bay of more neutral, high-density cloud, with clumps of neutral gas lying outside the bay area. This in turn lies on the perimeter of the Orion molecular cloud. The gas in the molecular cloud displays a range of velocities and turbulence, particularly around the core region. Relative movements are up to , with local variations of up to 50 km/s and possibly more. Observers have given names to various features in the Orion Nebula. The dark bay that extends from the north into the bright region is known as "Sinus Magnus", also called the "Fish's Mouth". The illuminated regions to both sides are called the "Wings". Other features include "The Sword", "The Thrust", and "The Sail".


Star formation

The Orion Nebula is an example of a
stellar nursery Star formation is the process by which dense regions within molecular clouds in interstellar space—sometimes referred to as "stellar nurseries" or "star-forming regions"— collapse and form stars. As a branch of astronomy, star formation inclu ...
where new stars are being born. Observations of the nebula have revealed approximately 700 stars in various stages of formation within the nebula. In 1979 observations with the Lallemand electronic camera at the Pic-du-Midi Observatory showed six unresolved high-ionization sources near the
Trapezium Cluster The Trapezium or Orion Trapezium Cluster, also known by its Bayer designation of Theta1 Orionis (θ1 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 Galile ...
. These sources were interpreted as partly ionized globules (PIGs). The idea was that these objects are being ionized from the outside by M42. Later observations with the
Very Large Array The Karl G. Jansky Very Large Array (VLA) is a centimeter-wavelength radio astronomy observatory in the southwestern United States built in the 1970s. It lies in central New Mexico on the Plains of San Agustin, between the towns of Magdalena, Ne ...
showed solar-system-sized condensations associated with these sources. Here the idea appeared that these objects might be low-mass stars surrounded by an evaporating protostellar accretion disk. In 1993 observations with the Hubble Space Telescope have yielded the major confirmation of
protoplanetary disk 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 not be considered an accretion disk; while the two are sim ...
s within the Orion Nebula, which have been dubbed '' proplyds''. HST has revealed more than 150 of these within the nebula, and they are considered to be systems in the earliest stages of
solar system formation There is evidence that the formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the ...
. The sheer number of them have been used as evidence that the formation of planetary systems is fairly common in the
universe The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...
. Stars form when clumps of
hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
and other gases in an
H II region An H II 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 of light year ...
contract under their own gravity. As the gas collapses, the central clump grows stronger and the gas heats to extreme temperatures by converting
gravitational potential energy Gravitational energy or gravitational potential energy is the potential energy an object with mass has due to the gravitational potential of its position in a gravitational field. Mathematically, it is the minimum Work (physics), mechanical work t ...
to
thermal energy The term "thermal energy" is often used ambiguously in physics and engineering. It can denote several different physical concepts, including: * Internal energy: The energy contained within a body of matter or radiation, excluding the potential en ...
. If the temperature gets high enough,
nuclear fusion Nuclear fusion is a nuclear reaction, reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutrons, neutron by-products. The difference in mass between the reactants and products is manifested as either the rele ...
will ignite and form a
protostar A protostar is a very young star that is still gathering mass from its parent molecular cloud. It is the earliest phase in the process of stellar evolution. For a low-mass star (i.e. that of the Sun or lower), it lasts about 500,000 years. The p ...
. The protostar is 'born' when it begins to emit enough radiative energy to balance out its gravity and halt
gravitational collapse Gravitational collapse is the contraction of an astronomical object due to the influence of its own gravity, which tends to draw matter inward toward the center of gravity. Gravitational collapse is a fundamental mechanism for structure formati ...
. Typically, a cloud of material remains a substantial distance from the star before the fusion reaction ignites. This remnant cloud is the protostar's protoplanetary disk, where planets may form. Recent
infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
observations show that protoplanetary disks in the Orion Nebula contain dust grains that are growing, beginning the process of forming
planetesimal Planetesimals () are solid objects thought to exist in protoplanetary disks and debris disks. Believed to have formed in the Solar System about 4.6 billion years ago, they aid study of its formation. Formation A widely accepted theory of pla ...
s. Once the protostar enters into its
main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...
phase, it is classified as a star. Even though most planetary disks can form planets, observations show that intense stellar radiation should have destroyed any proplyds that formed near the Trapezium group, if the group is as old as the low mass stars in the cluster. Since proplyds are found very close to the Trapezium group, it can be argued that those stars are much younger than the rest of the cluster members.


Stellar wind and effects

Once formed, the stars within the nebula emit a stream of charged particles known as a
stellar wind A stellar wind is a flow of gas ejected from the stellar atmosphere, upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spheri ...
. Massive stars and young stars have much stronger stellar winds than the
Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
. The wind forms shock waves or hydrodynamical instabilities when it encounters the gas in the nebula, which then shapes the gas clouds. The shock waves from stellar wind also play a large part in stellar formation by compacting the gas clouds, creating density inhomogeneities that lead to gravitational collapse of the cloud. There are three different kinds of shocks in the Orion Nebula. Many are featured in Herbig–Haro objects: *
Bow shock In astrophysics, bow shocks are shock waves in regions where the conditions of density and pressure change dramatically due to blowing stellar wind. Bow shock occurs when the magnetosphere of an astrophysical object interacts with the nearby fl ...
s are stationary and are formed when two particle streams collide with each other. They are present near the hottest stars in the nebula where the stellar wind speed is estimated to be thousands of kilometers per second and in the outer parts of the nebula where the speeds are tens of kilometers per second. Bow shocks can also form at the front end of stellar jets when the jet hits interstellar particles. * Jet-driven shocks are formed from jets of material sprouting off newborn
T Tauri stars T Tauri stars (TTS) are a class of variable stars that are less than about ten million years old. This class is named after the prototype, T Tauri, a young star in the Taurus star-forming region. They are found near molecular clouds and ide ...
. These narrow streams are traveling at hundreds of kilometers per second and become shocks when they encounter relatively stationary gases. * Warped shocks appear bow-like to an observer. They are produced when a jet-driven shock encounters gas moving in a cross-current. * The interaction of the stellar wind with the surrounding cloud also forms "waves" which are believed to be due to the hydrodynamical Kelvin-Helmholtz instability. The dynamic gas motions in M42 are complex, but are trending out through the opening in the bay and toward the Earth. The large neutral area behind the ionized region is currently contracting under its own gravity. There are also
supersonic Supersonic speed is the speed of an object that exceeds the speed of sound (Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) at sea level, this speed is approximately . Speeds greater than five times ...
'bullets' of gas piercing the hydrogen clouds of the Orion Nebula. Each bullet is ten times the diameter of
Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of Trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Su ...
's orbit and tipped with iron atoms glowing in the infrared. They were probably formed one thousand years earlier from an unknown violent event.


Evolution

Interstellar cloud An interstellar cloud is an accumulation of gas, plasma, and cosmic dust in galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium, the matter and radiation that exists in the space between ...
s like the Orion Nebula are found throughout
galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and 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 Sys ...
such as the
Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...
. They begin as gravitationally bound blobs of cold, neutral hydrogen, intermixed with traces of other elements. The cloud can contain hundreds of thousands of
solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...
es and extend for hundreds of light years. The tiny force of gravity that could compel the cloud to collapse is counterbalanced by the very faint pressure of the gas in the cloud. Whether due to collisions with a
spiral arm Spiral arms are a defining feature of spiral galaxies. They manifest as spiral-shaped regions of enhanced brightness within the galactic disc. Typically, spiral galaxies exhibit two or more spiral arms. The collective configuration of these arms i ...
, or through the shock wave emitted from
supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...
e, the atoms are precipitated into heavier molecules and the result is a molecular cloud. This presages the formation of stars within the cloud, usually thought to be within a period of 10–30 million years, as regions pass the
Jeans mass The Jeans instability is a concept in astrophysics that describes an instability that leads to the gravitational collapse of a cloud of gas or dust. It causes the collapse of interstellar gas clouds and subsequent star formation. It occurs when ...
and the destabilized volumes collapse into disks. The disk concentrates at the core to form a star, which may be surrounded by a protoplanetary disk. This is the current stage of evolution of the nebula, with additional stars still forming from the collapsing molecular cloud. The youngest and brightest stars we now see in the Orion Nebula are thought to be less than 300,000 years old, and the brightest may be only 10,000 years in age. Some of these collapsing stars can be particularly massive and can emit large quantities of ionizing
ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...
radiation. An example of this is seen with the Trapezium Cluster. Over time the ultraviolet light from the massive stars at the center of the nebula will push away the surrounding gas and dust in a process called
photoevaporation Photoevaporation is the process where energetic radiation ionises gas and causes it to disperse away from the ionising source. The term is typically used in an astrophysical context where ultraviolet radiation from hot stars acts on clouds of mate ...
. This process is responsible for creating the interior cavity of the nebula, allowing the stars at the core to be viewed from Earth. The largest of these stars have short life spans and will evolve to become supernovae. Within about 100,000 years, most of the gas and dust will be ejected. The remains will form a young open cluster: a cluster of bright, young stars surrounded by wispy filaments from the former cloud.Kroupa, P., Aarseth, S.J., Hurley, J. 2001, MNRAS, 321, 699
"The formation of a bound star cluster: from the Orion nebula cluster to the Pleiades"
/ref>


See also

*
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 o ...
*
Kleinmann–Low Nebula The Kleinmann–Low Nebula (also known as the Orion KL Nebula) is an active star forming region and place of a past explosion event in the Milky Way galaxy. It is a cluster of stars within a molecular cloud.Ferland pp191 The Kleinmann–Low Nebu ...
*
Flame Nebula __NOTOC__ The Flame Nebula, designated as NGC 2024 and Sh2-277, is an emission nebula in the constellation Orion (constellation), Orion. It is about 1350 light-years away. At that distance, the Flame Nebula lies within the Orion B cloud of the la ...
(NGC 2024) * Horsehead Nebula * '' Hubble 3D'' (2010), an IMAX film with an elaborate CGI fly-through of the Orion Nebula *
List of diffuse nebulae This is a list of diffuse nebulae. Most nebulae are diffuse, meaning that they do not have well-defined boundaries. Types of diffuse nebulae include emission nebulae and reflection nebulae. Emission and reflection nebulae See also *Lists of ast ...
*
List of Messier objects The Messier objects are a set of 110 astronomical objects catalogued by the French astronomer Charles Messier in his ' (''Catalogue of Nebulae and Star Clusters''). Because Messier was interested only in finding comets, he created a list of th ...
*
Messier 43 Messier 43 or M43, also known as De Mairan's Nebula and NGC 1982, is a star-forming nebula with a prominent H II region in the equatorial constellation of Orion. It was discovered by the French scientist Jean-Jacques d'Ortous de Mairan some t ...
, which is part of the Orion Nebula *
Messier 78 Messier 78 or M78, also known as NGC 2068, is a reflection nebula in the constellation Orion. It was discovered by Pierre Méchain in 1780 and included by Charles Messier in his catalog of comet-like objects that same year. M78 is the bright ...
, a reflection nebula *
New General Catalogue The ''New General Catalogue of Nebulae and Clusters of Stars'' (abbreviated NGC) is an astronomical catalogue of deep-sky objects compiled by John Louis Emil Dreyer in 1888. The NGC contains 7,840 objects, including galaxy, galaxies, star cluste ...
* Orion correlation theory *
Orion molecular cloud complex The Orion molecular cloud complex (or, simply, the Orion complex) is a star-forming region with stellar ages ranging up to 12 Myr. Two Molecular cloud#Giant molecular clouds, giant molecular clouds are a part of it, Orion A and Orion B. The stars ...
* Orion OB1


Notes


References


External links


Orion Nebula photographs taken by Andrew Ainslie Common in 1883, part of the London Science Museum's collection
* , University of South Wales
Orion Nebula observed by Chandra/HST

Orion Nebula observed by Gemini Observatory

Orion Nebula at ESA/Hubble


and specificall
NGC 1976

January 2006 Hubble Space Telescope image of the Orion Nebula

January 2006 Hubble Space Telescope image of the Trapezium cluster



Remarkable new views captured of Orion Nebula
SpaceFlight Now, 2001
NightSkyInfo.com – The Great Orion Nebula
*
Astronomy Picture of the Day Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include ...
*
Spitzer's Orion
2010 April 10 *

2009 December 22 *

2008 October 23 * *
ESO: Hidden Secrets of Orion’s Clouds
includes photos and animations {{Good article Messier objects H II regions NGC objects Orion molecular cloud complex Orion (constellation) Orion–Cygnus Arm Diffuse nebulae 16101126 Astronomical objects known since antiquity Articles containing video clips Star-forming regions 145