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The Orion Nebula (also known as Messier 42, M42, or NGC 1976) is a
diffuse 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 region ...
situated in 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. ...
, being south of Orion's Belt in the
constellation of Orion Orion is a prominent constellation located on the celestial equator and visible throughout the world. It is one of the most conspicuous and recognizable constellations in the night sky. It is named after Orion, a hunter in Greek mythology. ...
. It is one of the brightest
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 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 magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to norma ...
in the night sky with apparent magnitude 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 The "medium" is present further soon.-->interstellar space
to
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...
. The M42 nebula is estimated to be 24 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. 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 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 and
planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...
ary systems are formed from collapsing clouds of gas and dust. Astronomers have directly observed protoplanetary disks and
brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...
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 some
light pollution Light pollution is the presence of unwanted, inappropriate, or excessive use of artificial lighting. In a descriptive sense, the term ''light pollution'' refers to the effects of any poorly implemented lighting, during the day or night. Light po ...
. 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, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to obse ...
. The peak surface brightness of the central region of M42 is about 17 Mag/arcsec2 (about 14 milli
nits The National Institutes of Technology (NITs) are the central government-owned-public technical institutes under the ownership of Ministry of Education, Government of India. They are governed by the National Institutes of Technology, Scienc ...
) and the outer bluish glow has a peak surface brightness of 21.3 Mag/arcsec2 (about 0.27 millinits). (In the photos shown here the brightness, or
luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls with ...
, is enhanced by a large factor.) The Orion Nebula contains a very young
open cluster An open cluster is a type of star cluster made of up 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, an ...
, known as 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 Februa ...
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, 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 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 stars
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 dwarf with a mean apparent magnitude of +6.0. It is classifi ...
,
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 stell ...
, and Mu Columbae, 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
H-alpha (Hα) is a specific deep-red visible spectral line in the Balmer series with a wavelength of 656.28  nm in air and 656.46 nm in vacuum; it occurs when a hydrogen electron falls from its third to second lowest energy level. H-alph ...
recombination line
radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
at a
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tr ...
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 dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to ident ...
s at that time could explain it. There was some speculation that the lines were caused by a new element, and the name nebulium 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 ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have n ...
transition in doubly ionized oxygen, a so-called " forbidden transition". 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 of
Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...
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 and Saiph, and another, Alnitak at the tip of the "belt" of the imagined hunter, the vertices of a nearly perfect equilateral triangle with
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 sout ...
(including the Orion Nebula) in the middle of the triangle seen as the smudge of smoke from copal incense in a modern myth, or, in (the translation it suggests of) an ancient one, the literal or figurative embers of a fiery creation. Neither
Ptolemy Claudius Ptolemy (; grc-gre, Πτολεμαῖος, ; la, Claudius Ptolemaeus; AD) was a mathematician, astronomer, astrologer, geographer, and music theorist, who wrote about a dozen scientific treatises, three of which were of importanc ...
's ''
Almagest The ''Almagest'' is a 2nd-century Greek-language mathematical and astronomical treatise on the apparent motions of the stars and planetary paths, written by Claudius Ptolemy ( ). One of the most influential scientific texts in history, it can ...
'' nor Al Sufi's '' Book of Fixed Stars'' 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) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...
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 scientis ...
, on November 26, 1610, when he made a record of observing it with a
refracting telescope A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens as its objective to form an image (also referred to a dioptric telescope). The refracting telescope design was originally used in spyglasses an ...
purchased by his patron
Guillaume du Vair Guillaume du Vair (7 March 1556 – 3 August 1621) was a French author and lawyer. Life He was born in Paris. After taking holy orders, he exercised only legal functions for most of his career. However, from 1617 till his death he was Bishop ...
. The first published observation of the nebula was by the Jesuit mathematician and astronomer
Johann Baptist Cysat Johann Baptist Cysat (Latinized as Cysatus; in French, Jean-Baptiste Cysat) (c. 1587 – March 17, 1657) was a Swiss Jesuit mathematician and astronomer, after whom the lunar crater Cysatus is named. He was born in Lucerne, as the eighth of 14 ...
of
Lucerne Lucerne ( , ; High Alemannic: ''Lozärn'') or Luzern ()Other languages: gsw, Lozärn, label= Lucerne German; it, Lucerna ; rm, Lucerna . is a city in central Switzerland, in the German-speaking portion of the country. Lucerne is the capital o ...
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, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...
seen in 1618 and described how the nebula appeared through his telescope as: 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, 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 Februa ...
. (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) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He ...
in a February 4, 1617, although he did not notice the surrounding nebula – possibly due to the narrow field of vision of his early telescope.Galileo Galilei: Siderius Nuncius,
Venice Venice ( ; it, Venezia ; vec, Venesia or ) is a city in northeastern Italy and the capital of the Veneto Regions of Italy, region. It is built on a group of 118 small islands that are separated by canals and linked by over 400  ...
, 1610. English Translation published at Bard College, Hudson NY" October 9, 200
English Translation
) 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 (whose sketch was the first published in '' De systemate orbis cometici, deque admirandis coeli characteribus''). In 1659, Dutch scientist
Christiaan Huygens Christiaan Huygens, Lord of Zeelhem, ( , , ; also spelled Huyghens; la, Hugenius; 14 April 1629 – 8 July 1695) was a Dutch mathematician, physicist, engineer, astronomer, and inventor, who is regarded as one of the greatest scientists o ...
published the first detailed drawing of the central region of the nebula in ''Systema Saturnium''. Charles Messier 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. 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 ...
William Huggins used his visual
spectroscopy Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter ...
method to examine the nebula showing it, like other nebulae he had examined, was made up of "luminous gas". On September 30, 1880 Henry Draper used the new dry plate photographic process with an 11-inch (28 cm)
refracting telescope A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens as its objective to form an image (also referred to a dioptric telescope). The refracting telescope design was originally used in spyglasses an ...
to make a 51-minute exposure of the Orion Nebula, the first instance of astrophotography of a nebula in history. Another set of photographs of the nebula in 1883 saw a breakthrough in astronomical photography when amateur astronomer
Andrew Ainslie Common Andrew Ainslie Common 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 Common, a surgeon known for ...
used the dry plate process to record several images in exposures up to 60 minutes with a 36-inch (91 cm) reflecting telescope that he constructed in the backyard of his home in
Ealing Ealing () is a district in West London, England, west of Charing Cross in the London Borough of Ealing. Ealing is the administrative centre of the borough and is identified as a major metropolitan centre in the London Plan. Ealing was his ...
, 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
Marseilles Marseille ( , , ; also spelled in English as Marseilles; oc, Marselha ) is the prefecture of the French department of Bouches-du-Rhône and capital of the Provence-Alpes-Côte d'Azur region. Situated in the camargue region of southern Franc ...
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. 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 (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...
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 disks have been observed around most of the newly formed stars in the nebula, and the destructive effects of high levels of
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
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 (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...
s and possible brown dwarf
binary star A binary star 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 using a telescope as separate stars, in ...
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.


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 Reflection or reflexion may refer to: Science and technology * Reflection (physics), a common wave phenomenon ** Specular reflection, reflection from a smooth surface *** Mirror image, a reflection in a mirror or in water ** Signal reflection, in ...
e. The Nebula is part of a much larger nebula that is known as the Orion molecular cloud complex. The Orion molecular cloud complex extends throughout 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 ...
of Orion and includes Barnard's Loop, the Horsehead Nebula, M43, M78, and the Flame Nebula. 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 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 ...
) 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 10 km/s (22,000 mi/h), 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 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, 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 Februa ...
. 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 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 The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...
have yielded the major confirmation of protoplanetary disks 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 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 rest flattened into a ...
. The sheer numbers of them have been used as evidence that the formation of star systems is fairly common in the
universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the univers ...
. Stars form when clumps of
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
and other gases in an H II region 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 to thermal energy. If the temperature gets high enough, nuclear fusion will ignite and form a protostar. The protostar is 'born' when it begins to emit enough radiative energy to balance out its gravity and halt gravitational collapse. 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 those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
observations show that dust grains in these protoplanetary disks are growing, beginning on the path towards forming
planetesimal Planetesimals are solid objects thought to exist in protoplanetary disks and debris disks. Per the Chamberlin–Moulton planetesimal hypothesis, they are believed to form out of cosmic dust grains. Believed to have formed in the Solar System ...
s. Once the protostar enters into its
main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar He ...
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 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 spherically symmetric. ...
. Massive stars and young stars have much stronger stellar winds than the Sun. 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 shocks 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 iden ...
. 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 S ...
'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 generally an accumulation of gas, plasma, and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium, the matter and radiation that exists in the ...
s like the Orion Nebula are found throughout galaxies such as 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. ...
. 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 standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...
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, or through the shock wave emitted from
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 ...
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 In stellar physics, the Jeans instability causes the collapse of interstellar gas clouds and subsequent star formation, named after James Jeans. It occurs when the internal gas pressure is not strong enough to prevent gravitational collapse of a ...
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 (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
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 photo evaporation. 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 *
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 Nebu ...
* Flame Nebula (NGC 2024) * Horsehead Nebula * ''
Hubble 3D ''Hubble'' (also known as ''Hubble 3D'', ''IMAX: Hubble'', or ''IMAX: Hubble 3D'') is a 2010 American documentary film about Space Shuttle missions to repair and upgrade the Hubble Space Telescope. It is narrated by the actor Leonardo DiCaprio. ...
'' (2010), an IMAX film with an elaborate CGI fly-through of the Orion Nebula * List of diffuse nebulae * List of Messier objects * M43, which is part of the Orion Nebula * M78, a reflection nebula * New General Catalogue * Orion correlation theory * Orion molecular cloud complex *
Orion OB1 association Orion OB1 (Ori OB1) is a contingent group of several dozen hot giant stars of spectral types O and B in Orion. Associated are thousands of lower-mass stars, and a (smaller but significant) number of protostars. It is part of the larger Orion mo ...


Notes

  1. 1,270 × tan( 66′ / 2 ) = 12 ly. radius
  2. From temperate zones in the Northern Hemisphere, the nebula appears below the Belt of Orion; from temperate zones in the Southern Hemisphere the nebula appears above the Belt.
  3. C. Robert O'Dell commented about this Wikipedia article, "The only egregious error is the last sentence in the Stellar Formation section. It should actually read '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.'"


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
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Astronomy Picture of the Day Astronomy Picture of the Day (APOD) is a website provided by NASA and Michigan Technological University (MTU). According to the website, "Each day a different image or photograph of our universe is featured, along with a brief explanation wr ...
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Spitzer's Orion
2010 April 10 *

2009 December 22 *

2008 October 23 * *
ESO: Hidden Secrets of Orion’s Clouds
incl. 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