Orion Nebula
Encyclopedia
The Orion Nebula is a diffuse nebula situated south of Orion's Belt
. It is one of the brightest nebula
e, and is visible to the naked eye
in the night sky. M42 is located at a distance of and is the closest region of massive star formation
to Earth
. The M42 nebula is estimated to be 24 light years across. Older texts frequently referred 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. The nebula has revealed much about the process of how star
s and planet
ary systems are formed from collapsing clouds of gas and dust. Astronomers have directly observed protoplanetary disk
s, brown dwarf
s, intense and turbulent motions of the gas, and the photo-ionizing effects of massive nearby stars in the nebula. There are also supersonic
"bullets" of gas piercing the dense hydrogen clouds of the Orion Nebula. Each bullet is ten times the diameter of Pluto
's orbit and tipped with iron atoms glowing bright blue. They were probably formed one thousand years ago from an unknown violent event.
. The Orion Molecular Cloud Complex extends throughout the constellation
of Orion
and includes Barnard's Loop
, the Horsehead Nebula
, M43
, M78
and the Flame Nebula
. Stars are forming throughout the Orion Nebula, and due to this heat-intensive process the region is particularly prominent in the infrared
.
The nebula is visible with the naked eye even from areas affected by some light pollution
. 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
or a small telescope
.
The Orion Nebula contains a very young open cluster
, known as the Trapezium
due to the asterism
of its primary four stars. 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, along with many other stars, are still in their early years
. The Trapezium may be a component of the much-larger Orion Nebula Cluster, an association of about 2,000 stars within a diameter of 20 light years. Two million years ago this cluster may have been the home of the runaway stars AE Aurigae
, 53 Arietis
, and Mu Columbae
, which are currently moving away from the nebula at velocities greater than 100 km/s.
Observers have long noted a distinctive greenish tint to the nebula, in addition to regions of red and areas of blue-violet. The red hue is well-understood to be caused by Hα
recombination line radiation
at a wavelength
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
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, however, it was later determined that the green spectra was caused by a low-probability electron
transition in doubly ion
ized oxygen
, a so-called "forbidden transition". This radiation was all but impossible to reproduce in the laboratory because it depended on the quiescent and nearly collision-free environment found in deep space.
There is no known written record of the nebulosity in any astronomical records prior to the invention of the telescope in the 17th century. There has been speculation that the Mayans
of Central America
may have seen it as part of their "Three Hearthstones" of creation myth, suspected to have been made up of two stars at the base of Orion, Rigel
and Saiph, and one star at the tip of his belt, Alnitak, a nearly perfect triangle with Orion's Sword
(including the Orion Nebula) in the middle as the smudge of smoke from Copal
incense or the embers of creation. Neither Ptolemy
in the Almagest
nor Al Sufi
in his Book of Fixed Stars
noted this nebula, even though they both listed patches of nebulosity elsewhere in the night sky.This nebula was also not mentioned by Galileo
, even though he made telescope observations of this part of the constellation 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 defuse nebulous nature of the Orion Nebula is generally credited as being first discovered in 1610 when French
astronomer Nicolas-Claude Fabri de Peiresc
made a record of observed it with a refracting telescope
purchased by his patron Guillaume du Vair
. The first published observation of the nebula was a (somewhat ambiguous) account by Jesuit mathematician and astronomer Cysatus
of Lucerne
in a book about a bright comet
in 1618. It was independently discovered by several prominent astronomers in the following years, including Christiaan Huygens in 1656 (whose sketch was the first published in 1659). Charles Messier
first noted the nebula on March 4, 1769, and he also noted three of the stars in Trapezium. (The first detection of these three stars is now credited to Galileo in 1617, but he did not notice the surrounding nebula—possibly due to the narrow field of vision of his early telescope
.) Charles 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 William Huggins
used his visual spectroscopy
method to examine the nebula showing it, like other nebula 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
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 breakthrough in astronomical photography when amateur astronomer Andrew Ainslie Common
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, outside 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 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 further than the commonly accepted distance estimate of the period but was much closer to the modern value.
In 1993, the Hubble Space Telescope
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
s have been observed around most of the newly formed stars in the nebula, and the destructive effects of high levels of ultraviolet
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
s and possible brown dwarf binary star
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 0.054 M☉
and 0.034 M☉ respectively, with an orbital period of 9.8 days. Surprisingly, the more massive of the two also turned out to be the less luminous.
The entirety of the Orion Nebula extends across a 10° region of the sky, and includes neutral clouds of gas and dust
, associations of stars
, ionized volumes of gas
, and reflection nebula
e.
The nebula forms a roughly spherical cloud that peaks in density near the core. The cloud has a temperature ranging up to 10,000 K, but this temperature falls dramatically near the edge of the nebula. Unlike the density distribution, the 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.
The current astronomical model for the nebula consists of an ionized region roughly centered on Theta1 Orionis C, the star responsible for most of the ultraviolet
ionizing radiation. (It emits 3-4 times as much photoionizing light as the next brightest star, Theta2 Orionis A.) This 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.
Observers have given names to various features in the Orion Nebula. The dark lane that extends from the north toward the bright region is 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".
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.
Recent observations with the Hubble Space Telescope
have yielded the major discovery of protoplanetary disk
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. The sheer numbers of them have been used as evidence that the formation of star systems is fairly common in our universe
.
Stars form
when clumps of hydrogen
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
observations show that dust grains in these protoplanetary disks are growing, beginning on the path towards forming planetesimal
s.
Once the protostar enters into its main sequence
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.
. 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:
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.
Interstellar cloud
s like the Orion Nebula are found throughout galaxies
such as the Milky Way
. 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
es and extend for hundreds of light years. The tiny force of gravity that could compel the cloud to collapse is counter-balanced 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
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 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
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. The Pleiades
is a famous example of such a cluster.
Orion's Belt
The term Orion's Belt or the Belt of Orion may refer to:* Orion's Belt, an asterism consisting of three bright stars in a row in the constellation Orion* Orion's Belt, a 1985 film* Orion's Belt, a browser game...
. It is one of the brightest nebula
Nebula
A nebula is an interstellar cloud of dust, hydrogen gas, helium gas and other ionized gases...
e, and is visible to the naked eye
Naked eye
The naked eye is a figure of speech referring to human visual perception unaided by a magnifying or light-collecting optical device, such as a telescope or microscope. Vision corrected to normal acuity using corrective lenses is considered "naked"...
in the night sky. M42 is located at a distance of and is the closest region of massive star formation
Star formation
Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...
to Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. The M42 nebula is estimated to be 24 light years across. Older texts frequently referred 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. The nebula has revealed much about the process of how star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s and planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
ary systems are formed from collapsing clouds of gas and dust. Astronomers have directly observed protoplanetary disk
Protoplanetary disk
A protoplanetary disk is a rotating circumstellar disk of dense gas surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star...
s, brown dwarf
Brown dwarf
Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
s, intense and turbulent motions of the gas, and the photo-ionizing effects of massive nearby stars in the nebula. There are also supersonic
Supersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...
"bullets" of gas piercing the dense hydrogen clouds of the Orion Nebula. Each bullet is ten times the diameter of Pluto
Pluto
Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...
's orbit and tipped with iron atoms glowing bright blue. They were probably formed one thousand years ago from an unknown violent event.
General information
The Nebula is in fact part of a much larger nebula that is known as the Orion Molecular Cloud ComplexOrion Molecular Cloud Complex
The Orion Molecular Cloud Complex refers to a large group of bright nebula, dark clouds, and young stars located in the constellation of Orion. The cloud itself is between 1,500 and 1,600 light-years away and is hundreds of light-years across...
. The Orion Molecular Cloud Complex extends throughout the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Orion
Orion (constellation)
Orion, often referred to as The Hunter, is a prominent constellation located on the celestial equator and visible throughout the world. It is one of the most conspicuous, and most recognizable constellations in the night sky...
and includes Barnard's Loop
Barnard's Loop
Barnard's Loop is an emission nebula in the constellation of Orion. It is part of a Orion Molecular Cloud Complex which also contains the bright Horsehead and Orion nebulae. The loop takes the form of a large arc centred approximately on the Orion Nebula...
, the Horsehead Nebula
Horsehead Nebula
The Horsehead Nebula is a dark nebula in the constellation Orion. The nebula is located just to the south of the star Alnitak, which is farthest east on Orion's Belt, and is part of the much larger Orion Molecular Cloud Complex. The Horsehead Nebula is approximately 1500 light years from Earth...
, M43
Messier 43
Messier 43 is an H II region in the Orion constellation. It was discovered by Jean-Jacques Dortous de Mairan before 1731. The De Mairan's Nebula is part of the Orion Nebula, separated from the main nebula by a lane of dust. It is part of the much larger Orion Molecular Cloud Complex.-External...
, M78
Messier 78
The nebula Messier 78 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....
and the Flame Nebula
Flame Nebula
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....
. Stars are forming throughout the Orion Nebula, and due to this heat-intensive process the region is particularly prominent in the infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
.
The nebula is visible with the naked eye even from areas affected by some light pollution
Light pollution
Light pollution, also known as photopollution or luminous pollution, is excessive or obtrusive artificial light.The International Dark-Sky Association defines light pollution as:...
. 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
Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes when viewing distant objects...
or a small telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
.
The Orion Nebula contains a very young open cluster
Open cluster
An open cluster is a group 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, and many more are thought to exist...
, known as the Trapezium
Trapezium (astronomy)
The Trapezium, or Orion Trapezium Cluster 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 February 4, 1617 he sketched three of the stars , but missed the surrounding nebulosity...
due to the asterism
Asterism (astronomy)
In astronomy, an asterism is a pattern of stars recognized on Earth's night sky. It may form part of an official constellation, or be composed of stars from more than one. Like constellations, asterisms are in most cases composed of stars which, while they are visible in the same general direction,...
of its primary four stars. Two of these can be resolved into their component binary systems on nights with good seeing
Astronomical seeing
Astronomical seeing refers to the blurring and twinkling of astronomical objects such as stars caused by turbulent mixing in the Earth's atmosphere varying the optical refractive index...
, giving a total of six stars. The stars of the Trapezium, along with many other stars, are still in their early years
Star formation
Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...
. The Trapezium may be a component of the much-larger Orion Nebula Cluster, an association of about 2,000 stars within a diameter of 20 light years. Two million years ago this cluster may have been the home of the runaway stars AE Aurigae
AE Aurigae
AE Aurigae is a runaway star in the constellation Auriga; it lights the Flaming Star Nebula.AE Aurigae is a blue O-type main sequence dwarf with a mean apparent magnitude of +5.99. It is classified as an Orion type variable star and its brightness varies irregularly between magnitudes +5.78 and...
, 53 Arietis
53 Arietis
53 Arietis is a variable star of Beta Cephei type, alternatively denoted UW Arietis, in the constellation Aries. Its mean apparent magnitude is 6.13 and its spectral type is O or early B. It is a runaway star, thought to have been produced as a consequence of one of a pair of binary stars colliding...
, and Mu Columbae
Mu Columbae
Mu Columbae is a star in the constellation of Columba. It is one of the few O-class stars that is visible to the unaided eye. The star is known to lie approximately 1,300 light years from our solar system .This is a relatively fast rotating star that completes a full revolution approximately every...
, which are currently moving away from the nebula at velocities greater than 100 km/s.
Observers have long noted a distinctive greenish tint to the nebula, in addition to regions of red and areas of blue-violet. The red hue is well-understood to be caused by Hα
H-alpha
H-alpha is a specific red visible spectral line created by hydrogen with a wavelength of 656.28 nm, which occurs when a hydrogen electron falls from its third to second lowest energy level...
recombination line radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
at a wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
of 656.3 nm. The blue-violet coloration is the reflected radiation from the massive O-class
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
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
Spectral line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from a deficiency or excess of photons in a narrow frequency range, compared with the nearby frequencies.- Types of line spectra :...
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, however, it was later determined that the green spectra was caused by a low-probability electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
transition in doubly ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
ized oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, a so-called "forbidden transition". This radiation was all but impossible to reproduce in the laboratory because it depended on the quiescent and nearly collision-free environment found in deep space.
History
Maya civilization
The Maya is a Mesoamerican civilization, noted for the only known fully developed written language of the pre-Columbian Americas, as well as for its art, architecture, and mathematical and astronomical systems. Initially established during the Pre-Classic period The Maya is a Mesoamerican...
of Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
may have seen it as part of their "Three Hearthstones" of creation myth, suspected to have been made up of two stars at the base of Orion, Rigel
Rigel
Rigel is the brightest star in the constellation Orion and the sixth brightest star in the sky, with visual magnitude 0.18...
and Saiph, and one star at the tip of his belt, Alnitak, a nearly perfect triangle with Orion's Sword
Orion's Sword
The Orion's Sword is an astronomical asterism in the constellation Orion. It comprises three stars under the prominent asterism, Orion's Belt. M42, the Orion Nebula is located in the center...
(including the Orion Nebula) in the middle as the smudge of smoke from Copal
Copal
Copal is a name given to tree resin that is particularly identified with the aromatic resins used by the cultures of pre-Columbian Mesoamerica as ceremonially burned incense and other purposes...
incense or the embers of creation. Neither Ptolemy
Ptolemy
Claudius Ptolemy , was a Roman citizen of Egypt who wrote in Greek. He was a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in Egypt under Roman rule, and is believed to have been born in the town of Ptolemais Hermiou in the...
in the Almagest
Almagest
The Almagest is a 2nd-century mathematical and astronomical treatise on the apparent motions of the stars and planetary paths. Written in Greek by Claudius Ptolemy, a Roman era scholar of Egypt,...
nor Al Sufi
Abd Al-Rahman Al Sufi
Abd al-Rahman al-Sufi was a Persian astronomer also known as Abd ar-Rahman as-Sufi, or Abd al-Rahman Abu al-Husayn, Abdul Rahman Sufi, Abdurrahman Sufi and known in the west as Azophi; the lunar crater Azophi and the minor planet 12621 Alsufi are named after him...
in his Book of Fixed Stars
Book of Fixed Stars
The Book of Fixed Stars is an astronomical text written by Abd al-Rahman al-Sufi around 964. The book was written in Arabic, although the author himself was Persian...
noted this nebula, even though they both listed patches of nebulosity elsewhere in the night sky.This nebula was also not mentioned by Galileo
Galileo Galilei
Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...
, even though he made telescope observations of this part of the constellation 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 defuse nebulous nature of the Orion Nebula is generally credited as being first discovered in 1610 when French
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
astronomer Nicolas-Claude Fabri de Peiresc
Nicolas-Claude Fabri de Peiresc
Nicolas-Claude Fabri de Peiresc was a French astronomer, antiquary and savant who maintained a wide correspondence with scientists and was a successful organizer of scientific inquiry...
made a record of observed it with a refracting telescope
Refracting telescope
A refracting or refractor telescope is a type of optical telescope that uses a lens as its objective to form an image . The refracting telescope design was originally used in spy glasses and astronomical telescopes but is also used for long focus camera lenses...
purchased by his patron Guillaume du Vair
Guillaume du Vair
Guillaume du Vair was a French author and lawyer.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 of Lisieux. His reputation is that of a lawyer, a statesman and a man of letters...
. The first published observation of the nebula was a (somewhat ambiguous) account by Jesuit mathematician and astronomer Cysatus
Johann Baptist Cysat
Johann Baptist Cysat was a Swiss Jesuit mathematician and astronomer, after whom the lunar crater Cysatus is named...
of Lucerne
Lucerne
Lucerne is a city in north-central Switzerland, in the German-speaking portion of that country. Lucerne is the capital of the Canton of Lucerne and the capital of the district of the same name. With a population of about 76,200 people, Lucerne is the most populous city in Central Switzerland, and...
in a book about a bright comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
in 1618. It was independently discovered by several prominent astronomers in the following years, including Christiaan Huygens in 1656 (whose sketch was the first published in 1659). Charles Messier
Charles Messier
Charles Messier was a French astronomer most notable for publishing an astronomical catalogue consisting of deep sky objects such as nebulae and star clusters that came to be known as the 110 "Messier objects"...
first noted the nebula on March 4, 1769, and he also noted three of the stars in Trapezium. (The first detection of these three stars is now credited to Galileo in 1617, but he did not notice the surrounding nebula—possibly due to the narrow field of vision of his early telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
.) Charles 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.
William Huggins
Sir William Huggins, OM, KCB, FRS was an English amateur astronomer best known for his pioneering work in astronomical spectroscopy.-Biography:...
used his visual spectroscopy
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
method to examine the nebula showing it, like other nebula he had examined, was made up of "luminous gas". On September 30, 1880 Henry Draper
Henry Draper
Henry Draper was an American doctor and amateur astronomer. He is best known today as a pioneer of astrophotography.-Life and work:...
used the new dry plate
Dry plate
Dry plate, also known as gelatin process, is an improved type of photographic plate. It was invented by Dr. Richard L. Maddox in 1871, and by 1879 it was so well introduced that the first dry plate factory had been established...
photographic process with an 11-inch (28 cm) refracting telescope
Refracting telescope
A refracting or refractor telescope is a type of optical telescope that uses a lens as its objective to form an image . The refracting telescope design was originally used in spy glasses and astronomical telescopes but is also used for long focus camera lenses...
to make a 51-minute exposure of the Orion Nebula, the first instance of astrophotography
Astrophotography
Astrophotography is a specialized type of photography that entails recording images of astronomical objects and large areas of the night sky. The first photographs of an astronomical object were taken in the 1840s, but it was not until the late 19th century that advances in technology allowed for...
of a nebula in history. Another set of photographs of the nebula in 1883 saw breakthrough in astronomical photography when amateur astronomer Andrew Ainslie Common
Andrew Ainslie Common
Andrew Ainslie Common FRS was an English amateur astronomer best known for his pioneering work in astrophotography.-Biography:...
used the dry plate process to record several images in exposures up to 60 minutes with a 36-inch (91 cm) reflecting telescope
Reflecting telescope
A reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the refracting telescope which, at that time, was a design that suffered from...
that he constructed in the backyard of his home in Ealing, outside London. These images for the first time showed stars and nebula detail too faint to be seen by the human eye.
In 1902, Vogel
Hermann Carl Vogel
Hermann Carl Vogel was a German astronomer. He was born in Leipzig, Kingdom of Saxony.Vogel pioneered the use of the spectroscope in astronomy...
and Eberhard discovered differing velocities within the nebula and by 1914 astronomers at Marseilles 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
Robert Julius Trumpler
Robert Julius Trumpler was a Swiss-American astronomer....
noted that the fainter stars near the Trapezium
Trapezium (astronomy)
The Trapezium, or Orion Trapezium Cluster 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 February 4, 1617 he sketched three of the stars , but missed the surrounding nebulosity...
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 further than the commonly accepted distance estimate of the period but was much closer to the modern value.
In 1993, the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
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
Protoplanetary disk
A protoplanetary disk is a rotating circumstellar disk of dense gas surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star...
s have been observed around most of the newly formed stars in the nebula, and the destructive effects of high levels of ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
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 dwarf
Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
s and possible brown dwarf binary star
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
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 0.054 M☉
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
and 0.034 M☉ 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
Interstellar cloud
Interstellar cloud is the generic name given to 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. Depending on the density, size and temperature of a given cloud, the hydrogen in it...
, associations of stars
Star cluster
Star clusters or star clouds are groups of stars. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars which are gravitationally bound, while open clusters, more loosely clustered groups of stars, generally contain less than...
, ionized volumes of gas
H II region
An H II region is a large, low-density cloud of partially ionized gas in which star formation has recently taken place. The short-lived, blue stars forged in these regions emit copious amounts of ultraviolet light, ionizing the surrounding gas...
, and reflection nebula
Reflection nebula
In Astronomy, reflection nebulae are clouds of dust which are simply reflecting the light of a nearby star or stars. The energy from the nearby star, or stars, is insufficient to ionize the gas of the nebula to create an emission nebula, but is enough to give sufficient scattering to make the dust...
e.
The nebula forms a roughly spherical cloud that peaks in density near the core. The cloud has a temperature ranging up to 10,000 K, but this temperature falls dramatically near the edge of the nebula. Unlike the density distribution, the 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.
The current astronomical model for the nebula consists of an ionized region roughly centered on Theta1 Orionis C, the star responsible for most of the ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
ionizing radiation. (It emits 3-4 times as much photoionizing light as the next brightest star, Theta2 Orionis A.) This 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.
Observers have given names to various features in the Orion Nebula. The dark lane that extends from the north toward the bright region is 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".
Stellar formation
Recent observations with the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
have yielded the major discovery of protoplanetary disk
Protoplanetary disk
A protoplanetary disk is a rotating circumstellar disk of dense gas surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star...
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. The sheer numbers of them have been used as evidence that the formation of star systems is fairly common in our universe
Universe
The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...
.
Stars form
Stellar evolution
Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years to trillions of years .Stellar evolution is not studied by observing the life of a single...
when clumps of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
and other gases in an H II region
H II region
An H II region is a large, low-density cloud of partially ionized gas in which star formation has recently taken place. The short-lived, blue stars forged in these regions emit copious amounts of ultraviolet light, ionizing the surrounding gas...
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
Thermal energy
Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....
. If the temperature gets high enough, nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
will ignite and form a protostar
Protostar
A protostar is a large mass that forms by contraction out of the gas of a giant molecular cloud in the interstellar medium. The protostellar phase is an early stage in the process of star formation. For a one solar-mass star it lasts about 100,000 years...
. The protostar is 'born' when it begins to emit enough radiative energy to balance out its gravity and halt gravitational collapse
Gravitational collapse
Gravitational collapse is the inward fall of a body due to the influence of its own gravity. In any stable body, this gravitational force is counterbalanced by the internal pressure of the body, in the opposite direction to the force of gravity...
.
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
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
observations show that dust grains in these protoplanetary disks are growing, beginning on the path towards forming planetesimal
Planetesimal
Planetesimals are solid objects thought to exist in protoplanetary disks and in debris disks.A widely accepted theory of planet formation, the so-called planetesimal hypothesis of Viktor Safronov, states that planets form out of cosmic dust grains that collide and stick to form larger and larger...
s.
Once the protostar enters into its main sequence
Main sequence
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 Hertzsprung and Henry Norris Russell...
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 windStellar wind
A stellar wind is a flow of neutral or charged 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.Different types of stars have...
. Massive stars
OB star
OB stars are hot, massive stars of spectral types O or B which form in loosely organized groups called OB associations. They are short lived, and thus don't move very far from where they were formed within their life. During their lifetime, they will emit copious amounts of ultraviolet radiation...
and young stars
T Tauri star
T Tauri stars are a class of variable stars named after their prototype – T Tauri. They are found near molecular clouds and identified by their optical variability and strong chromospheric lines.-Characteristics:...
have much stronger stellar winds than the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. 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.
- Bow shockBow shockA bow shock is the area between a magnetosphere and an ambient medium. For stars, this is typically the boundary between their stellar wind and the interstellar medium....
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 particlesInterstellar mediumIn astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
.
- Jet-driven shocks are formed from jets of material sprouting off newborn T Tauri stars. 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 instabilityKelvin-Helmholtz instabilityThe Kelvin–Helmholtz instability, after Lord Kelvin and Hermann von Helmholtz, can occur when velocity shear is present within a continuous fluid, or when there is sufficient velocity difference across the interface between two fluids. One example is wind blowing over a water surface, where the...
.
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.
Evolution
Interstellar cloud
Interstellar cloud is the generic name given to 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. Depending on the density, size and temperature of a given cloud, the hydrogen in it...
s like the Orion Nebula are found throughout galaxies
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
such as the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
. 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
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
es and extend for hundreds of light years. The tiny force of gravity that could compel the cloud to collapse is counter-balanced 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
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
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 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
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
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
Photo evaporation
Photoevaporation denotes the process when a planet is stripped of its atmosphere due to high energy photons and other electromagnetic radiation. If a photon interacts with an atmospheric molecule, the molecule is accelerated and its temperature increased...
. 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. The Pleiades
Pleiades (star cluster)
In astronomy, the Pleiades, or Seven Sisters , is an open star cluster containing middle-aged hot B-type stars located in the constellation of Taurus. It is among the nearest star clusters to Earth and is the cluster most obvious to the naked eye in the night sky...
is a famous example of such a cluster.
See also
- List of Messier objects
- List of diffuse nebulae
- New General CatalogueNew General CatalogueThe New General Catalogue of Nebulae and Clusters of Stars is a well-known catalogue of deep sky objects in astronomy. It contains 7,840 objects, known as the NGC objects...
- Orion Nebula in fiction
- Hubble 3DHubble 3DHubble 3D, also known as IMAX: Hubble 3D, is a 2010 documentary film about the Hubble Space Telescope repair mission.-Content:"Through the power of IMAX 3D, Hubble 3D will enable movie-goers to journey through distant galaxies to explore the grandeur and mysteries of our celestial surroundings, and...
(2010), an IMAX film with an elaborate CGI "fly-through" of the Orion Nebula
External links
- Animated tour of the Orion Nebula, University of Glamorgan
- Orion Nebula observed by Chandra/HST
- Orion Nebula observed by Gemini Observatory
- Orion Nebula at ESA/Hubble
- Messier 42, SEDS Messier pages and specifically NGC 1976.
- January 2006 Hubble Space Telescope image of the Orion Nebula
- January 2006 Hubble Space Telescope image of the Trapezium cluster
- Orion Nebula M42, Hubble Images
- Remarkable new views captured of Orion Nebula, SpaceFlight Now, 2001.
- NightSkyInfo.com - The Great Orion Nebula
- Computer visualization of Orion Nebula. Data gathered from the Hubble Space Telescope and ground-based sensors were combined to form a 3D volume visualization of the nebula. Narration of the planetarium-like flythrough describes notable features and views from angles not possible from Earth. Link contains downloadable MPEG and Quicktime movies of flythrough.
- Astronomy Picture of the DayAstronomy Picture of the DayAstronomy Picture of the Day is a website provided by NASA and Michigan Technological University . According to the website, "Each day a different image or photograph of our universe is featured, along with a brief explanation written by a professional astronomer."The photograph is not necessarily...
- Spitzer's Orion 2010 April 10
- Planetary Systems Now Forming in Orion 2009 December 22
- Great Orion Nebulae 2008 October 23