Difference between revisions of "Nebula" - New World Encyclopedia

From New World Encyclopedia
(Reformatted Notes.)
 
(37 intermediate revisions by 5 users not shown)
Line 1: Line 1:
{{Claimed}}
+
{{Images OK}}{{Approved}}{{copyedited}}
{{otheruses}}
+
[[Image:Eagle nebula pillars.jpg|thumb|right|250px|The "Pillars of Creation" from the [[Eagle Nebula]].]]
[[Image:Triangulum.nebula.full.jpg|thumb|250px|The Triangulum Emission Nebula [[NGC 604]]]]
 
[[Image:Eagle nebula pillars.jpg|thumb|right|250px|The "Pillars of Creation" from the [[Eagle Nebula]]]]
 
  
A '''nebula''' (from [[Latin]]: "mist,"<ref>[http://www.etymonline.com/index.php?term=nebula Nebula] Online Etymology Dictionary. Retrieved September 19, 2007.</ref> pl. ''nebulae'' or ''nebulæ'') is an [[interstellar cloud]] of [[cosmic dust|dust]], [[hydrogen]] gas and [[Plasma (physics)|plasma]]. It is the first stage of a star's cycle. Originally ''nebula'' was a general name for any extended [[astronomy|astronomical]] [[astronomical object|object]], including [[galaxy|galaxies]] beyond the [[Milky Way]] (some examples of the older usage survive; for example, the [[Andromeda Galaxy]] was referred to as the ''[[Andromeda (mythology)|Andromeda]] Nebula'' before galaxies were discovered by [[Edwin Hubble]]). Nebulae often form star-forming regions, such as in the [[Eagle Nebula]]. This nebula is depicted in one of [[NASA]]'s most famous images, the "Pillars of Creation." In these regions the formations of gas, dust and other materials 'clump' together to form larger masses, which attract further matter, and eventually will become big enough to form stars. The remaining materials are then believed to form planets, and other solar system objects.
+
A '''nebula''' (pl. ''nebulae,'' ''nebulæ,'' or ''nebulas;'' derived from the [[Latin]] word for "mist" or "cloud"<ref>''Online Etymology Dictionary,'' [http://www.etymonline.com/index.php?term=nebula Nebula.] Retrieved June 23, 2008.</ref>) is an [[interstellar cloud]] of [[cosmic dust|dust]], [[hydrogen]] gas, and [[Plasma (matter)|plasma]]. Originally, the term ''nebula'' was a general name for any extended [[astronomy|astronomical]] [[astronomical object|object]], including [[galaxy|galaxies]] beyond the [[Milky Way]]. For example, the [[Andromeda Galaxy]] was once referred to as the ''[[Andromeda (mythology)|Andromeda]] Nebula'' before galaxies were discovered by [[Edwin Hubble]]. Many nebulae (known as diffuse nebulae) have poorly defined boundaries; others (such as planetary nebulae) may be described as discrete objects with identifiable boundaries.
 +
{{toc}}
 +
Nebulae often contain star-forming regions, as observed in the [[Eagle Nebula]], depicted in [[NASA]]'s famous image known as the ''Pillars of Creation.'' In these regions, the formations of gas, dust, and other materials "clump" together to form larger masses, which attract further matter and eventually become large enough to form stars. The remaining materials are then believed to form planets and other objects similar to those in the [[Solar System]].
 +
[[Image:Triangulum.nebula.full.jpg|thumb|250px|The Triangulum Emission Nebula [[NGC 604]].]]
  
 
==Formation==
 
==Formation==
 
[[Image:Ngc2024 2mass.jpg|thumb|200px|left|NGC 2024, The [[Flame Nebula]].]]
 
[[Image:Ngc2024 2mass.jpg|thumb|200px|left|NGC 2024, The [[Flame Nebula]].]]
 +
Many nebulae are formed during the gravitational collapse of diffuse gases in the [[interstellar medium]] (ISM). As the material collapses under its own weight, massive stars may form in the center, and their ultraviolet radiation ionizes the surrounding gas, making it visible at optical wavelengths. Examples of this type of nebula are the [[Rosette Nebula]] and the [[Pelican Nebula]]. These nebulae vary in size, depending on the size of the original cloud of gas. The number of stars formed can vary as well. At the sites of star formation, the newly formed stars are sometimes known as young, loose clusters.
  
Many nebulae form from the gravitational collapse of diffuse gas in the [[interstellar medium]] or ISM. As the material collapses under its own weight, massive stars may form in the center, and their ultraviolet radiation ionizes the surrounding gas, making it visible at optical wavelengths. An example of this type of nebula is the [[Rosette Nebula]] or the [[Pelican Nebula]]. The size of these nebulae, known as HII regions, varies depending on the size of the original cloud of gas, and the number of stars formed can vary too. As the sites of star formation, the formed stars are sometimes known as a young, loose cluster.
+
Some nebulae are formed as a consequence of [[supernova]] explosions, which are the death throes of massive, short-lived stars. The material thrown off from the supernova explosion is ionized by the supernova remnant. One of the best examples of this is the [[Crab Nebula]], in Taurus. It is the result of a supernova recorded in the year 1054, and the center of the nebula contains a [[neutron star]], created during the explosion.
  
Some nebulae are  formed as the result of [[supernova]] explosions, the death throes of massive, short-lived stars. The material thrown off from the supernova explosion is ionised by the supernova remnant. One of the best examples of this is the [[Crab Nebula]], in Taurus. It is the result of a recorded supernova in the year 1054 and at the center of the nebula is a [[neutron star]], created during the explosion.
+
Other nebulae may form as [[planetary nebula]]e (discussed below). This is the final stage of the life of a low-mass star, such as our [[Sun]]. [[Star]]s that have a mass of up to 8-10 solar masses evolve into [[red giant]]s and slowly lose their outer layers during pulsations in their atmosphere. When a star has lost a sufficient amount of material, its temperature increases and the [[ultraviolet]] radiation it emits is capable of [[ion]]izing the surrounding nebula.<ref>fuseweb.llnl.gov, [http://fusedweb.llnl.gov/CPEP/Chart_Pages/5.Plasmas/Nebula.html Planetary Nebulae.] Retrieved June 24, 2008.</ref>
 
 
Other nebulae may form as [[planetary nebula]]e. This is the final stage of a low-mass star's life, like our own Sun. [[Star]]s with a mass up to 8-10 solar masses evolve into [[red giant]]s and slowly lose their outer layers during pulsations in their atmospheres. When a star has lost a sufficient amount of material, its temperature increases and the [[ultraviolet]] radiation it emits is capable of [[ion]]izing the surrounding nebula that it has thrown off.
 
  
 
==Diffuse nebulae==
 
==Diffuse nebulae==
 
 
[[Image:Omega Nebula.jpg|thumb|150px|The [[Omega Nebula]], an example of an [[emission nebula]].]]
 
[[Image:Omega Nebula.jpg|thumb|150px|The [[Omega Nebula]], an example of an [[emission nebula]].]]
  
 
[[Image:Pleiades.jpg|thumb|150px|The [[Pleiades (star cluster)|Pleiades]].  The diffuse nebulae near the stars are examples of [[reflection nebula]].]]
 
[[Image:Pleiades.jpg|thumb|150px|The [[Pleiades (star cluster)|Pleiades]].  The diffuse nebulae near the stars are examples of [[reflection nebula]].]]
  
Most nebulae can be described as [[diffuse nebula]]e, which means that they are extended and contain no well-defined boundaries.<ref name="Messier">[http://seds.lpl.arizona.edu/messier/diffuse.html The Messier Catalog: Diffuse Nebulae]. University of Illinois. Retrieved September 19, 2007.</ref> In visible light these nebulae may be divided into [[emission nebula]]e and [[reflection nebula]]e, a categorization that depends on how the light we see is created. Emission nebulae contain [[ion]]ized gas (mostly ionized [[hydrogen]]) that produces [[spectral line]] emission.<ref name="shu1982">Shu, F.H. 1982. ''The Physical Universe''. Mill Valley, CA: University Science Books. ISBN 0-935702-05-9.</ref>  These emission nebulae are often called [[HII regions]]; the term "HII" is used in professional astronomy to refer to ionized hydrogen.  In contrast to emission nebulae, reflection nebulae do not produce siginicant amounts of visible light by themselves but instead reflect light from nearby stars.<ref name="shu1982" /> 
+
Most nebulae can be described as [[diffuse nebula]]e, which means that they are extended and have no well-defined boundaries.<ref name="Messier">University of Illinois, [http://seds.lpl.arizona.edu/messier/diffuse.html The Messier Catalog: Diffuse Nebulae.] Retrieved September 19, 2007.</ref> In visible light, these nebulae may be divided into [[emission nebula]]e and [[reflection nebula]]e, a categorization that is based on how the light we detect was created.
  
[[Image:Horsehead-Hubble.jpg|left|thumb|150px|The [[Horsehead Nebula]], an example of a [[dark nebula]].]]
+
* Emission nebulae: They consist of a plasma of [[ion]]ized gas, mostly ionized [[hydrogen]] and electrons.<ref name="shu1982">F.H. Shu, ''The Physical Universe'' (Mill Valley, CA: University Science Books, 1982, ISBN 0935702059).</ref> When the ions recombine with the electrons, they emit spectral lines, particularly the red line of hydrogen.<ref>''FusEdWeb Fusion Energy Education,'' [http://fusedweb.llnl.gov/CPEP/Chart_Pages/5.Plasmas/Nebula/Emission.html Emission Nebulae.] Retrieved June 24, 2008.</ref> Thus, emission nebulae have a reddish glow. These nebulae are often called [[HII region]]s, which refers to the presence of ionized hydrogen.
  
Dark nebulae are similar to diffuse nebulae, but they are not seen by their emitted or reflected light. Instead, they are seen as dark clouds in front of more distant stars or in front of emission nebulae.<ref name="shu1982" />
+
* Reflection nebulae: Unlike emission nebulae, reflection nebulae do not produce significant amounts of visible light on their own. Rather, they contain dust particles that scatter (reflect) the light of nearby stars.<ref name="shu1982" /> Given that light is scattered more readily in the blue region than in the red, reflection nebulae tend to appear bluish.<ref>''Fusion Energy Education,'' [http://fusedweb.llnl.gov/CPEP/Chart_Pages/5.Plasmas/Nebula/Reflection.html Reflection Nebulae.] Retrieved June 24, 2008.</ref>
  
Although these nebulae appear different at optical wavelengths, they all appear to be bright sources of emission at [[infrared]] wavelengths. This emission comes primarily from the [[cosmic dust|dust]] within the nebulae.<ref name="shu1982" />
+
[[Image:Horsehead-Hubble.jpg|left|thumb|150px|The [[Horsehead Nebula]], an example of a [[dark nebula]].]]
 
 
{{clear}}
 
  
==Specific types of nebulae==
+
Dark nebulae are similar to diffuse nebulae, but they are not seen by their emitted or reflected light. Instead, they are observed as dark clouds in front of more distant stars or in front of emission nebulae.<ref name="shu1982" />
While diffuse nebulae have poorly-defined boundaries, a few nebulae may actually be described as discrete objects with identifiable boundaries.
 
  
===Planetary nebulae===
+
Although these nebulae appear different at optical wavelengths, they all appear to be bright sources of emission at [[infrared]] wavelengths. This emission comes primarily from the [[cosmic dust|dust]] within the nebulae.<ref name="shu1982" />
  
 +
==Planetary nebulae==
 
[[Image:NGC6543.jpg|right|thumb|150px|The [[Cat's Eye Nebula]], an example of a [[planetary nebula]].]]
 
[[Image:NGC6543.jpg|right|thumb|150px|The [[Cat's Eye Nebula]], an example of a [[planetary nebula]].]]
  
[[Planetary nebula]]e are nebulae that form from the gaseous shells that are ejected from low-mass [[red giant]]s when they transform into [[white dwarf]]s.<ref name="shu1982" />   These nebulae are emission nebulae with spectral emission that is similar to the emission nebulae found in [[star formation]] regions.<ref name="shu1982" /> Technically, they are a type of HII region because the majority of hydrogen will be ionised. However, planetary nebulae are denser and more compact than the emission nebulae in star formation regions.<ref name="shu1982" /> Planetary nebulae are so called because the first astronomers who observed these objects thought that the nebulae resembled the disks of planets, although they are not at all related to planets.<ref name="s">Chaisson, E., S. McMillan. 1995. ''Astronomy: a beginner's guide to the universe''. Upper Saddle River, NJ: Prentice-Hall. ISBN 0-13-733916-X.</ref>
+
[[Planetary nebula]]e are nebulae that form from the gaseous shells ejected from low-mass [[red giant]]s (toward the end of the star's life) when they transform into [[white dwarf]]s.<ref name="shu1982" /> These nebulae are emission nebulae, with spectral emission that is similar to the emission nebulae found in [[star formation]] regions.<ref name="shu1982" /> Technically, they are a type of HII region because most of their hydrogen content will be ionized. However, planetary nebulae are denser and more compact than the emission nebulae in star formation regions.<ref name="shu1982" />
 
 
{{clear}}
 
  
====Protoplanetary nebula====
+
The name "planetary nebulae" was given because the astronomers who first observed these objects thought that they resembled the disks of planets. However, they are not related to planets at all.<ref name="s">E. Chaisson and S. McMillan, ''Astronomy: A Beginner's Guide to the Universe'' (Upper Saddle River, NJ: Prentice-Hall, ISBN 013733916X).</ref>
  
 +
==Protoplanetary nebula==
 
[[Image:PIA04533.jpg|thumb|100px|left|The [[Red Rectangle Nebula]], an example of a [[protoplanetary nebula]].]]
 
[[Image:PIA04533.jpg|thumb|100px|left|The [[Red Rectangle Nebula]], an example of a [[protoplanetary nebula]].]]
  
A [[protoplanetary nebula]] (PPN) is an astronomical object which is at the short-lived episode during a star's rapid stellar evolution between the late [[asymptotic giant branch]] (LAGB) phase and the subsequent planetary nebula (PN) phase.<ref name="sahaietal2005">Sahai, R., C. Sánchez Contreras, M. Morris. 2005. [http://adsabs.harvard.edu/abs/2005ApJ...620..948S Starfish Preplanetary Nebula: IRAS 19024+0044]. ''Astrophysical Journal''. 620:948-960. Retrieved September 19, 2007.</ref> A PPN emits strong in infrared radiation, and is a kind of reflection nebula. The exact point when a PPN becomes a planetary nebula (PN) is defined by the temperature of the central star.
+
A [[protoplanetary nebula]] (PPN) is an astronomical object that is at the short-lived episode during a star's rapid stellar evolution between the late [[asymptotic giant branch]] (LAGB) phase and the subsequent planetary nebula (PN) phase.<ref name="sahaietal2005">R. Sahai, C. Sánchez Contreras, and M. Morris, [http://adsabs.harvard.edu/abs/2005ApJ...620..948S A Starfish Preplanetary Nebula: IRAS 19024+0044,] ''Astrophysical Journal'' 620:948-960. Retrieved June 24, 2008.</ref> A PPN emits strong infrared radiation, and it is a kind of reflection nebula. The exact stage when a PPN becomes a planetary nebula (PN) is defined by the temperature of the central star.
 
 
{{clear}}
 
  
===Supernova remnants===
+
==Supernova remnants==
  
 
[[Image:Crab Nebula.jpg|thumb|150px|The [[Crab Nebula]], an example of a [[supernova remnant]].]]
 
[[Image:Crab Nebula.jpg|thumb|150px|The [[Crab Nebula]], an example of a [[supernova remnant]].]]
  
A [[supernova]] occurs when a high-mass star reaches the end of its life. When [[nuclear fusion]] ceases in the core of the star, the star collapses inward on itself. The gas falling inward either rebounds or gets so strongly heated that it expands outwards from the core, thus causing the star to explode.<ref name="shu1982"/> The expanding shell of gas form a [[supernova remnant]], a special type of [[diffuse nebula]].<ref name="shu1982"/>   Although much of the optical and [[X-ray]] emission from supernova remnants originates from ionized gas, a substantial amount of the [[radio]] emission is a form of non-thermal emission called [[synchrotron emission]].<ref name="shu1982"/> This emission originates from high-velocity and [[electrons]] oscillating within [[magnetic field]]s.
+
A [[supernova]] is produced when a high-mass star reaches the end of its life. When [[nuclear fusion]] ceases in the core of the star, the star collapses inward on itself and forms a neutron core. The gas falling inward either rebounds or gets so strongly heated that it expands outward from the core, thus causing the star to explode.<ref name="shu1982"/> The expanding shell of gas forms what is called a [[supernova remnant]], a special type of [[diffuse nebula]].<ref name="shu1982"/> Although much of the optical and [[X-ray]] emission from supernova remnants originates from ionized gas, a substantial amount of the [[radio]] emission is a form of nonthermal emission called [[synchrotron emission]].<ref name="shu1982"/> This latter emission originates from near the core of the remnant as high-velocity [[electron]]s move within the [[magnetic field]] of the neutron star.<ref>''Fusion Energy Education,'' [http://fusedweb.llnl.gov/CPEP/Chart_Pages/5.Plasmas/Nebula/Supernova.html Supernova Remnants.] Retrieved June 24, 2008.</ref>
 
 
{{clear}}
 
 
 
==Notable named nebulae==
 
  
 +
==Examples of notable named nebulae==
 +
*[[Barnard's Loop]]
 +
*[[Cat's Eye Nebula]]
 +
*[[Crab Nebula]]
 
*[[Eagle Nebula]]
 
*[[Eagle Nebula]]
 
*[[Eta Carinae Nebula]]
 
*[[Eta Carinae Nebula]]
 +
*[[Horsehead Nebula]]
 +
*[[Hourglass Nebula]]
 
*[[Orion Nebula]]
 
*[[Orion Nebula]]
*[[Hourglass Nebula]]
+
*[[Red Square Nebula]]
*[[Horsehead Nebula]]
+
*[[Ring Nebula]]
 
*[[Rosette Nebula]]
 
*[[Rosette Nebula]]
*[[Ring Nebula]]
 
*[[Crab Nebula]]
 
*[[Cat's Eye Nebula]]
 
*[[Barnard's Loop]]
 
*[[Red Square Nebula]]
 
 
*[[Tarantula Nebula]]
 
*[[Tarantula Nebula]]
 
==See also==
 
 
* [[Star]]
 
* [[Orion Molecular Cloud Complex]]
 
* [[Magellanic Cloud]]
 
* [[Messier object]]
 
  
 
== Notes ==
 
== Notes ==
Line 84: Line 68:
  
 
==References==
 
==References==
 +
* Coe, Steven R. 2007. ''Nebulae and How to Observe Them.'' London: Springer. ISBN 978-1846284823.
 +
* Gurzadyan, Grigor A. 1997. ''The Physics and Dynamics of Planetary Nebulae.'' Berlin: Springer. ISBN 3540609652.
 +
* Kaufmann, William J. 1978. ''Stars and Nebulas''. San Francisco: W.H. Freeman. ISBN 3540609652.
 +
* O'Dell, C. Robert. 2003. ''The Orion Nebula: Where Stars Are Born''. Cambridge, MA: Belknap. ISBN 067401183X.
  
Lightner, G. Samuel. "Nebulae: Fuzzy Patches in Space." ''FusedWed.pppl.gov/CPEP'' 18 December 2000.
 
 
---. "Nebulae." ''FusedWed.pppl.gov/CPEP'' 17 November 2005.
 
 
---. "Reflection Nebulae." ''FusedWed.pppl.gov/CPEP'' 18 December 2000.
 
 
---. "Emission Nebulae." ''FusedWed.pppl.gov/CPEP'' 18 December 2000.
 
 
---. "Planetary Nebulae." ''FusedWed.pppl.gov/CPEP'' 18 December 2000.
 
 
---. "Supernova Remnants." ''FusedWed.pppl.gov/CPEP''18 December 2000.
 
 
==External links==
 
  
* [http://fusedweb.pppl.gov fusedweb.pppl.gov]
 
* [http://www.geocities.com/altoid22001/starformation.html Information on star formation]
 
  
 
[[Category:Physical sciences]]
 
[[Category:Physical sciences]]

Latest revision as of 16:07, 11 November 2022

The "Pillars of Creation" from the Eagle Nebula.

A nebula (pl. nebulae, nebulæ, or nebulas; derived from the Latin word for "mist" or "cloud"[1]) is an interstellar cloud of dust, hydrogen gas, and plasma. Originally, the term nebula was a general name for any extended astronomical object, including galaxies beyond the Milky Way. For example, the Andromeda Galaxy was once referred to as the Andromeda Nebula before galaxies were discovered by Edwin Hubble. Many nebulae (known as diffuse nebulae) have poorly defined boundaries; others (such as planetary nebulae) may be described as discrete objects with identifiable boundaries.

Nebulae often contain star-forming regions, as observed in the Eagle Nebula, depicted in NASA's famous image known as the Pillars of Creation. In these regions, the formations of gas, dust, and other materials "clump" together to form larger masses, which attract further matter and eventually become large enough to form stars. The remaining materials are then believed to form planets and other objects similar to those in the Solar System.

The Triangulum Emission Nebula NGC 604.

Formation

NGC 2024, The Flame Nebula.

Many nebulae are formed during the gravitational collapse of diffuse gases in the interstellar medium (ISM). As the material collapses under its own weight, massive stars may form in the center, and their ultraviolet radiation ionizes the surrounding gas, making it visible at optical wavelengths. Examples of this type of nebula are the Rosette Nebula and the Pelican Nebula. These nebulae vary in size, depending on the size of the original cloud of gas. The number of stars formed can vary as well. At the sites of star formation, the newly formed stars are sometimes known as young, loose clusters.

Some nebulae are formed as a consequence of supernova explosions, which are the death throes of massive, short-lived stars. The material thrown off from the supernova explosion is ionized by the supernova remnant. One of the best examples of this is the Crab Nebula, in Taurus. It is the result of a supernova recorded in the year 1054, and the center of the nebula contains a neutron star, created during the explosion.

Other nebulae may form as planetary nebulae (discussed below). This is the final stage of the life of a low-mass star, such as our Sun. Stars that have a mass of up to 8-10 solar masses evolve into red giants and slowly lose their outer layers during pulsations in their atmosphere. When a star has lost a sufficient amount of material, its temperature increases and the ultraviolet radiation it emits is capable of ionizing the surrounding nebula.[2]

Diffuse nebulae

The Omega Nebula, an example of an emission nebula.
The Pleiades. The diffuse nebulae near the stars are examples of reflection nebula.

Most nebulae can be described as diffuse nebulae, which means that they are extended and have no well-defined boundaries.[3] In visible light, these nebulae may be divided into emission nebulae and reflection nebulae, a categorization that is based on how the light we detect was created.

  • Emission nebulae: They consist of a plasma of ionized gas, mostly ionized hydrogen and electrons.[4] When the ions recombine with the electrons, they emit spectral lines, particularly the red line of hydrogen.[5] Thus, emission nebulae have a reddish glow. These nebulae are often called HII regions, which refers to the presence of ionized hydrogen.
  • Reflection nebulae: Unlike emission nebulae, reflection nebulae do not produce significant amounts of visible light on their own. Rather, they contain dust particles that scatter (reflect) the light of nearby stars.[4] Given that light is scattered more readily in the blue region than in the red, reflection nebulae tend to appear bluish.[6]
The Horsehead Nebula, an example of a dark nebula.

Dark nebulae are similar to diffuse nebulae, but they are not seen by their emitted or reflected light. Instead, they are observed as dark clouds in front of more distant stars or in front of emission nebulae.[4]

Although these nebulae appear different at optical wavelengths, they all appear to be bright sources of emission at infrared wavelengths. This emission comes primarily from the dust within the nebulae.[4]

Planetary nebulae

The Cat's Eye Nebula, an example of a planetary nebula.

Planetary nebulae are nebulae that form from the gaseous shells ejected from low-mass red giants (toward the end of the star's life) when they transform into white dwarfs.[4] These nebulae are emission nebulae, with spectral emission that is similar to the emission nebulae found in star formation regions.[4] Technically, they are a type of HII region because most of their hydrogen content will be ionized. However, planetary nebulae are denser and more compact than the emission nebulae in star formation regions.[4]

The name "planetary nebulae" was given because the astronomers who first observed these objects thought that they resembled the disks of planets. However, they are not related to planets at all.[7]

Protoplanetary nebula

The Red Rectangle Nebula, an example of a protoplanetary nebula.

A protoplanetary nebula (PPN) is an astronomical object that is at the short-lived episode during a star's rapid stellar evolution between the late asymptotic giant branch (LAGB) phase and the subsequent planetary nebula (PN) phase.[8] A PPN emits strong infrared radiation, and it is a kind of reflection nebula. The exact stage when a PPN becomes a planetary nebula (PN) is defined by the temperature of the central star.

Supernova remnants

The Crab Nebula, an example of a supernova remnant.

A supernova is produced when a high-mass star reaches the end of its life. When nuclear fusion ceases in the core of the star, the star collapses inward on itself and forms a neutron core. The gas falling inward either rebounds or gets so strongly heated that it expands outward from the core, thus causing the star to explode.[4] The expanding shell of gas forms what is called a supernova remnant, a special type of diffuse nebula.[4] Although much of the optical and X-ray emission from supernova remnants originates from ionized gas, a substantial amount of the radio emission is a form of nonthermal emission called synchrotron emission.[4] This latter emission originates from near the core of the remnant as high-velocity electrons move within the magnetic field of the neutron star.[9]

Examples of notable named nebulae

  • Barnard's Loop
  • Cat's Eye Nebula
  • Crab Nebula
  • Eagle Nebula
  • Eta Carinae Nebula
  • Horsehead Nebula
  • Hourglass Nebula
  • Orion Nebula
  • Red Square Nebula
  • Ring Nebula
  • Rosette Nebula
  • Tarantula Nebula

Notes

  1. Online Etymology Dictionary, Nebula. Retrieved June 23, 2008.
  2. fuseweb.llnl.gov, Planetary Nebulae. Retrieved June 24, 2008.
  3. University of Illinois, The Messier Catalog: Diffuse Nebulae. Retrieved September 19, 2007.
  4. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 F.H. Shu, The Physical Universe (Mill Valley, CA: University Science Books, 1982, ISBN 0935702059).
  5. FusEdWeb Fusion Energy Education, Emission Nebulae. Retrieved June 24, 2008.
  6. Fusion Energy Education, Reflection Nebulae. Retrieved June 24, 2008.
  7. E. Chaisson and S. McMillan, Astronomy: A Beginner's Guide to the Universe (Upper Saddle River, NJ: Prentice-Hall, ISBN 013733916X).
  8. R. Sahai, C. Sánchez Contreras, and M. Morris, A Starfish Preplanetary Nebula: IRAS 19024+0044, Astrophysical Journal 620:948-960. Retrieved June 24, 2008.
  9. Fusion Energy Education, Supernova Remnants. Retrieved June 24, 2008.

References
ISBN links support NWE through referral fees

  • Coe, Steven R. 2007. Nebulae and How to Observe Them. London: Springer. ISBN 978-1846284823.
  • Gurzadyan, Grigor A. 1997. The Physics and Dynamics of Planetary Nebulae. Berlin: Springer. ISBN 3540609652.
  • Kaufmann, William J. 1978. Stars and Nebulas. San Francisco: W.H. Freeman. ISBN 3540609652.
  • O'Dell, C. Robert. 2003. The Orion Nebula: Where Stars Are Born. Cambridge, MA: Belknap. ISBN 067401183X.

Credits

New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

The history of this article since it was imported to New World Encyclopedia:

Note: Some restrictions may apply to use of individual images which are separately licensed.