Orion Nebula

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Emission nebula
Dates of the Orion Nebula

A false color image of the Orion Nebula composed of various images taken by the Hubble Space Telescope in 2004 and 2005. The De Mairans Nebula can be seen on the left above the center of the picture. North is up.

A false color image of the Orion Nebula composed of various images taken by the Hubble Space Telescope in 2004 and 2005. The De Mairans Nebula can be seen on the left above the center of the picture . North is up.
AladinLite
Constellation Orion
Position
equinox :  J2000.0 , epoch : J2000.0
Right ascension 05 h 35 m 16.5 s
declination −05 ° 23 ′ 23 ″
Appearance

Apparent brightness  (visual) 3.7 mag  
Apparent brightness  (B-band) 4 likes 
Angular expansion 65/60 
Ionizing source
description θ 1 Orionis C1 
Type star 
Physical data

Affiliation Milky Way 
distance  1350 ± 23 ly
(414 ± 7 pc )
Dimensions 700–2100 M ☉
diameter 24 ly
Age 3 million years
story

discovery N.-CF de Peiresc
Date of discovery 1610
Catalog names
 NGC  1976 •  GC  1179 •  h  360 •  M  42 • LBN  974 • Sh 2 -281

The Orion Nebula (catalog name M 42 or NGC 1976 ) is an emission nebula in the constellation Orion . Due to the relatively large apparent brightness of its center above the 4th magnitude, the nebula is clearly visible to the naked eye as part of the sword of Orion south of the three stars of the Orion belt . It has an angular extent of about one degree.

The Orion Nebula is a part of the interstellar molecular cloud OMC-1, which in turn belongs to the giant molecular cloud Orion A , which in turn belongs to the Orion molecular cloud complex . It consists mainly of hydrogen . Stars are formed in the nebula , the ionizing radiation of which makes the nebula shine in the visible range. It is therefore also classified as an H-II area . With a distance of about 414  parsecs (1350  light years ) it is one of the most active star formation areas in the galactic neighborhood , which is why it is a preferred object of investigation for the study of star formation. It is expected to develop into an open star cluster similar to the Pleiades .

The main source of ionization of the Orion Nebula is the star θ¹ Orionis C1 , which, with more than 200,000 times the luminosity of the sun, is also one of the most luminous stars known. The immediately neighboring and similarly constituted De Mairans Nebula , however, has a different ionizing source and is therefore not part of the Orion Nebula.

Discovery and Exploration

Chinese star map, around 700: The constellation Shen (參) with the Orion Nebula drawn as a red dot is similar to the constellation Orion

Although the Orion Nebula is the only emission nebula visible to the naked eye under good conditions , its special shape was not mentioned in European, Arabic and Chinese scriptures before the 17th century: the around 2000 year old Almagest , al-Sūfī's book of fixed stars and the modern Uranometria only note the Orion Nebula as a star with magnitude 3 to 4. After detailed observations became possible with the first telescopes , the Orion Nebula developed into one of the best-researched star formation regions due to its proximity.

Outer shape

The earliest descriptions of the Orion Nebula were vague and received little attention. For example, a handwritten note by the French astronomer Nicolas-Claude Fabri de Peiresc from 1610 records the multiple observations of an object consisting of two stars in a glowing “cloud” in the middle of the constellation Orion. However, it is not certain whether it actually refers to the Orion Nebula with the two apparent stars θ¹ and θ² Orionis, as has been assumed since the beginning of the 20th century. The observation of the nebula, published casually by Johann Baptist Cysat and Volpert Motzel in 1619, compared it to a comet . Just like the sketching and cataloging by Giovanni Battista Hodierna from 1654, this was only published in the 19th / 20th Century taken up again and recognized in its importance.

With the outline drawing of the nebula published in 1659, Christiaan Huygens was therefore considered the discoverer for a long time . The particularly bright area of ​​the nebula he depicted was called the Huygens region. Charles Messier recorded the nebula in his catalog, first published in 1774, as the 42nd entry, supplemented by a detailed illustration. Friedrich von Hahn described its structure shortly afterwards

“... as a bright scintillating cloud. But it looks as if the completely black fog in its vicinity extended to behind that cloud, which thereby resembles a shiny fabric on a dark ground. "

In the years that followed, improved telescopes made it possible to detect increasingly faint parts of the Orion Nebula, so that increasingly detailed images were created, even though the individual perception of the observer clearly influenced the image.

Messier was already considering whether one could deduce from different depictions of the Huygens region that it would change over time. Wilhelm Herschel saw this as proven in 1811 based on his own and previous observations. Around 70 years later, Edward Singleton Holden compiled the current state of knowledge in a comprehensive monograph. He discussed the various images and came to the conclusion that despite the different representations, the Orion Nebula had probably not changed its shape since the middle of the 18th century, but had changed its brightness .

Henry Draper took the first photo of the nebula in 1880, which is also considered to be the first astrophotographic record of a non-stellar object outside the solar system . The technique was quickly improved, and the Andrew Ainslie Commons excellent picture from 1883 already showed more detail than could be seen with the naked eye through the same telescope. The previously suspected changes in the Orion Nebula, however, did not confirm the subsequent photographs. With the understanding of the physics of the Orion Nebula beginning at this time, further investigations increasingly aimed at certain aspects of physics; the external shape as the sole objective of the investigation increasingly faded into the background. Examples from the 21st century are the high-resolution images from the Hubble space telescope and images from the VLT and the space telescopes Spitzer , WISE and Herschel for the infrared range .

Structure and composition

Galileo Galileo's sketch of the components of θ Orionis, which he recognized with the help of a telescope in 1617: The close group c, g, i forms part of the trapezium , where g denotes the brightest star θ 1 Orionis C ; a and b are now referred to as θ² Orionis B and A.

Even though Galileo Galilei did not mention the nebula, in 1617 he determined with the help of his telescope that θ Orionis is only apparently a central star. Instead of a single star, he observed five different components, three of which form a close group. Later, Jean-Dominique Cassini discovered a fourth star belonging to this group, which was then called the trapezium . In the following years, with the help of improved telescopes, more stars could be assigned to the trapezium and the surroundings could also be cataloged. At the end of the 19th century, several hundred stars of the 1.5 ° diameter cluster in the Orion Nebula had already been recorded. However, the total visible light of the stars was not enough to explain the glow of the nebula, as William Derham recognized in 1733 .

The cloud complex in Orion, observed by William Henry Pickering and Edward Barnard at the end of the 19th century, begins above the three belt stars , extends down to Rigel and is contoured on the left by Barnard's Loop . Investigations in the early 1920s showed that the Orion Nebula, slightly below the center of the image, is a light-emitting part of the cloud complex.

The extraordinary "pea green" color of the Orion Nebula was recorded by William Lassell in the middle of the 19th century and subsequent spectroscopic investigations by William Huggins indicated the gaseous nature of the nebula surrounding the stars as early as 1865. In addition to initially unknown green spectral lines , those from hydrogen were clearly visible. The regionally different distribution of the various gases was shown by Johannes Franz Hartmann in 1905 on the basis of photographs with narrow-band filters , although the unknown spectral lines could only be assigned to ionized oxygen in the 1920s . By determining the Doppler shift of the known spectral lines of hydrogen, Hermann Carl Vogel determined currents within the nebula in 1902 . Henri Buisson , Charles Fabry and Henry Bourget confirmed this in 1914 by interferometric measurement of the spectral lines and derived an upper limit of 15,000  Kelvin for the gas temperature from the line width . Soon after, long-exposure images showed that the Orion Nebula is the glowing part of a much larger cloud . Some researchers then suspected that the ultraviolet radiation emitted by the stars of the trapezium heats the gases surrounding them and causes them to glow through ionization. With the knowledge gained in the meantime that one of the spectral lines originates from the element oxygen, a more precise temperature determination of the luminous gases was possible in 1931. Taking currents into account, the result was a value of 11,000 Kelvin , which was only slightly different from the results of subsequent investigations, which indicated a temperature of 10,000 Kelvin in the center. At this time, Walter Baade and Rudolph Minkowski took measurements on some of the brightest stars in order to explain their atypical spectra. The spectrometric investigations also showed that the mist must contain large amounts of carbon and iron-containing dust particles. Further spectroscopy of the nebula showed that, in addition to hydrogen, it also contains around ten percent helium and that the proportions of oxygen, carbon, neon, nitrogen, sulfur and argon are less than one percent - which is similar to the sun. Around 90 percent of the elements magnesium, silicon and iron, which are also present with less than one percent, are bound as oxide in the stellar dust.

Visualization of the three-dimensional structure of the Orion Nebula and the position of the embedded stars in front of the ionization front and behind a veil of neutral gas. Excerpt from an animation for the IMAX , the perspective is roughly perpendicular to the view from the telescope.

The most powerful source of ultraviolet radiation was identified as the optically brightest star in the trapezium, θ¹ Orionis C ; detailed physical models for the excitation of the nebula to glow by ultraviolet radiation followed in the 1950s. Investigations in the 1960s and 1970s showed that the flow velocities were dependent on the degree of ionization and thus on the distance to θ¹ Orionis C and showed more and more clearly that the trapezoidal stars in front of the molecular cloud lie in a spherical cavity and only their boundary layer is ionized. The thickness of 0.1  pc and the three-dimensional position of the ionization front was determined in the early 1990s and then elaborately visualized in the following years. Further developed models were used, which could be further improved at a later point in time, in particular with the help of high-resolution images of the nebula emission from the Hubble space telescope. It was also during this period that a veil of non-ionized gas was discovered in the foreground, characterized in more detail and added to the models. The resulting models provide more precise information about the particle density in the ionization front, which in the Huygens region reaches around 9,000 ionized atoms per cubic centimeter - a value typical for H-II regions .

Long exposure infrared image , created with the Very Large Telescope and the HAWK-I camera
Two recordings of the trapezoid cluster in the Orion Nebula, with different spectra.
Left visible light: Distribution of hydrogen (green), oxygen (blue) and nitrogen (red).
Right infrared: stars emerge.

In the early 1930s, Robert Julius Trumpler succeeded in identifying a few stars in the vicinity of the trapezium more closely using infrared images, in which a color filter blocked visible light and thus many of the nebula's spectral lines . He described what he called a "Trapezium cluster" (trapezoid cluster) with the extension of one minute of arc , which includes 41 stars. In 1953 , Guillermo Haro reported an even larger area with a radius of ten arc minutes around the trapezoidal stars and named it the "Orion Nebula Cluster". However, later observations revealed that these are not separate areas. Rather, the aforementioned clusters belong to a single cluster of around 3500 stars, the total mass of which is probably 700–2100 solar masses . Further infrared investigations with a larger telescope and more sensitive detectors were able to track down a large number of brown dwarfs and objects of planetary mass in 2008 . It turned out that there are considerably more objects of this type in the Orion Nebula than had been assumed up to then. Subsequent investigations with the upgraded WFC3 infrared camera of the Hubble Space Telescope completed the picture.

Period of origin

Emerging stars with circumstellar disks (orange and black) in the Orion Nebula, section of the image taken by the Hubble Space Telescope

At the beginning of the 19th century, Wilhelm Herschel already suspected that the matter contained in the nebulae would form stars through gravitational compression. Photographic and spectroscopic studies in the beginning of the 20th century substantiate this thesis, but understanding of the timing did not develop until later. At the end of the 1950s, Kaj Aage Gunnar Strand first compared the color-brightness diagrams of the Orion cluster with those of another star cluster that had previously been made by Merle Walker. From this he concluded that it was less than three million years old. On the basis of the existing T-Tauri stars and their age of 300,000 years, calculated from different old photographic recordings, he suspected, however, that the gravitational star formation would still have to continue. Investigations in the infrared spectrum such as those by Eric Becklin and Gerry Neugebauer from 1965 gave examples of star formation that was still ongoing shortly afterwards. They show u. a. an object only one arc minute away from θ¹ Orionis and only detectable in the infrared range. This new Becklin-Neugebauer object , named after its discoverer, with a temperature of only 700 K was then classified as a protostar . At the same time, the nearby Kleinmann Low Nebula , which is also very cold and also only detectable in the infrared , was discovered, in which a number of stars are formed. In 1969, Walker measured a large number of stars photometrically in different spectral ranges in areas with low nebula emissions and was thus able to determine their age at around three million years. About twenty years later, George Howard Herbig and Donald Terndrup applied the same method to the visible and infrared spectral range and found that the stars must be predominantly younger than a million years. At the beginning of the 1990s, high-resolution images from the Hubble Space Telescope succeeded in identifying a large number of stars in the process of forming on the basis of their circumstellar disks (Proplyd).

The Orion Nebula itself was probably not visible 50,000 years ago, as the young O and B stars were surrounded by the molecular cloud. In the early 1960s, Franz Daniel Kahn, Thuppalay Kochu Govinda Menon and Peter O. Vanderport calculated that the molecular cloud must have been partially evaporated by photoionization from these stars in the meantime. An indentation formed around the more than a thousand stars of the star cluster subsequently made it possible for the stars to be seen from Earth.

Area of ​​origin

Image of the area around the Orion Nebula in the far infrared

With the help of the millimeter and sub-millimeter range of observations available at the end of the 20th century, the Orion molecular cloud was examined more closely. The so-called integral-shaped filament was discovered. Recent studies with the Atacama Large Millimeter / submillimeter Array show that this filament consists of a multitude of fibers in which star formation takes place.

Distance and size

The first determination of the distance of the Orion Nebula was still fraught with clear uncertainties and discrepancies. With the advent of photography in astronomy, William Henry Pickering determined the proper motion of some stars in the Orion Nebula and, in 1895, estimated a distance of 1,000 light years from this. A good twenty years later he then compared the apparent brightness of stars with stars of the same spectral class and known distance and derived 2000 parsecs (6520 light years) from this spectroscopic parallax . Two years later he changed the value to 500 parsecs after Jacobus C. Kapteyn had calculated 180 parsecs using the same method. Using the embedded trapezium and the nearby NGC-1981 star clusters, Trumpler again determined distances of 500 and 400 parsecs in 1931, again using spectroscopic parallax; a star cluster size classification developed by him yielded 660 or 470 parsecs. Distance determinations from the 1940s to 1980s showed between 300 and 483 parsecs. Only one star in the Orion Nebula was suitable for a satellite-based triangulation by Hipparcos , which means that the result is subject to considerable uncertainty. An exact trigonometric distance measurement was finally made in 2007 with the help of the Very Long Baseline Array on four radio stars and resulted in a distance of 414 ± 7 parsecs; Another measurement in 2014–2016 with the same instrument resulted in 388 ± 5 parsecs. Initial results from Gaia , the successor to Hipparcos, provided a distance of 403 parsecs in 2018, including 378 stars from the Orion Nebula cluster. It was found that stars lying a little further north and south on the filament are about 8 parsec closer, which at least partially explains the remaining differences between the measurements.

Since the Orion Nebula does not have a sharp contour, the size of the nebula awarded depends on the choice of method of defining its edge. In the middle of the 20th century, Stewart Sharpless cataloged a large number of H-II regions and ascribed an apparent diameter of 60 arc minutes to the Orion Nebula for comparison purposes. At a distance of 1350 light years, this angle corresponds to an extension of 24 light years. Lynds' Catalog of Bright Nebulae notes 60 × 90 arc minutes.

Observability

Location of the Orion Nebula in the constellation Orion , as it can be seen with the naked eye (designation of the brightest stars according to Uranometria ): The Orion Nebula lies 5 ° south of the middle of the belt stars ζ, ε and δ and is marked with a circle around θ Orionis.

The Orion Nebula is best observed in the winter months , when it is 30–40 ° high in the south in Central Europe in the evening, or in October around 5 a.m. Despite its brightness, only a slight blurring, which is atypical for stars, can be perceived with the naked eye; It is only with the aid of tools that it is possible to differentiate between the nebula and the stars in it. The four components θ¹ Orionis and θ² Orionis A – C as well as filaments of the nebula can already be seen with a 10 × 50 binocular . Less bright parts of the nebula and also the dark indentation in the Huygens region can already be seen with binoculars of the type 10 × 70; the Orion Nebula can thus be observed in an area of ​​30 × 45 arc minutes.

Photo of the Orion Nebula with a 30 cm telescope opening , post-processed .

With more magnifying telescopes, the four trapezoidal stars can be made out individually, and the outline of the Huygens region can be clearly seen. Telescopes with an opening width of 12 cm also reveal small, bright islands and dark channels in this region, a 60 cm telescope already shows a level of detail that is comparable to the sketch from observations through the Leviathan telescope . The sketch by John Herschel gives an impression of the perceptibility of the entire nebula in a telescope of this size. The glow of the four trapezoidal stars and of θ² Orionis dominates the nebula structures much more than these sketches can show.

The green-bluish color of the Huygens region is already perceptible with telescope diameters of less than 30 cm. This impression increases with increasing openness. From 30 cm the edges of this region appear orange-red and with a diameter of 50 cm, colors outside this region also appear. Nevertheless - compared to detailed color photos, which, like the images above, are created by long exposure times and post-processing , the color impression is much weaker even with high-light telescopes.

reception

The Orion Nebula has also gained some notoriety outside of astronomy . This is reflected above all in myths, in literature, in films and also in video games. For example, it is considered part of a star constellation in the culture of the Mesoamerican people of the Maya as an image of the smoke of a fireplace or is symbolized by them by a torch. As an independent object, the Orion Nebula sometimes represents a significant part of the storyline in works of science fiction , as in the computer game Elite: Dangerous , during which a virtual image of the nebula can even be visited by the player. The Orion Nebula has also found its way into popular and everyday culture. This includes the musical and graphic work of various artists, but also recordings of the Hubble space telescope on posters, puzzles, T-shirts and other everyday objects. In Japan and Hungary, stamp blocks with the Orion Nebula as a motif were issued in 2018.

literature

Web links

More images and general articles

Commons : Orion Nebula  - collection of images, videos and audio files

Reports on current research (selection)

Individual evidence

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  19. ^ Digitized at Commons
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  76. ^ The Gould's Belt Distances Survey (GOBELINS) II. Distances and Structure toward the Orion Molecular Clouds . In: The Astrophysical Journal . 834, No. 2, 2017. bibcode : 2017ApJ ... 834..142K . doi : 10.3847 / 1538-4357 / 834/2/142 .
  77. ↑ Michael A. Kuhn, Lynne A. Hillenbrand, Alison Sills, Eric D. Feigelson, Konstantin V. Getman: Kinematics in Young Star Clusters and Associations with Gaia DR2 . In: Accepted for publication in the Astrophysical Journal. . 2018. arxiv : 1807.02115 . bibcode : 2018arXiv180702115K .
  78. ↑ Patrick Moore : The Amateur Astronomer . Springer, London 2006, ISBN 978-1-84628-286-7 , pp. 224 ( books.google.de ).
  79. ^ A b c d e f g h Ronald Stoyan , Stefan Binnewies, Susanne Friedrich: Atlas of the Messier objects . 2006, ISBN 978-3-938469-07-1 , pp. 177-180 .
  80. ↑ Linda Schele, Khristaan ​​D. Villela: Creation, Cosmos, and the Imagery of Palenque and Copan . In: Eighth Palenque Round Table X . 1993, pp. 1-18.
  81. ↑ Barbara Tedlock: Earth rites and moon cycles: Mayan synodic and sidereal lunar reckoning . 1983.
  82. ^ Matthew G. Looper: Creation Mythology at Naranjo . In: Texas Notes on Precolumbian Art, Writing, and Culture . 1992.
  83. ↑ Compare Nebulae in fiction, Orion Nebula of the English language Wikipedia.
  84. ↑ Offer of some articles and a piece of music ( Memento from February 4, 2017 in the Internet Archive )
  85. ↑ https://grapee.jp/en/94007
  86. ↑ https://www.buyhungarianstamps.com/products/hungary-2018-for-youth-philately-interstellar-ms-mnh
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