NGC 6543, The Cat's Eye Nebula

NGC 6853, The Dumbbell Nebula

A planetary nebula is an astronomical object consisting of a glowing shell of gas and plasma formed by certain types of stars at the end of their lives. The name originates from a similarity in appearance to giant planets when viewed through a small optical telescope, and is unrelated to planets of the solar system. They are a relatively short-lived phenomenon, lasting a few tens of thousands of years, compared to a typical stellar lifetime of several billion years. About 1,500 are known to exist in the Milky Way Galaxy. Download high resolution version (800x874, 64 KB)X-ray/optical composite image of NGC 6543, the Cats Eye Nebula (X-ray: NASA/UIUC/Y.Chu et al. ... Download high resolution version (800x874, 64 KB)X-ray/optical composite image of NGC 6543, the Cats Eye Nebula (X-ray: NASA/UIUC/Y.Chu et al. ... The Cats Eye Nebula (NGC 6543) is a planetary nebula in the constellation of Draco. ... Image File history File links Size of this preview: 752 × 600 pixelsFull resolution (910 × 726 pixel, file size: 59 KB, MIME type: image/jpeg) Image of Dumbbell Nebula (M27) taken by Robert J. Vanderbei using 10 Ritchey-Chretien telescope and Starlight Express SXV-H9 CCD camera. ... Image File history File links Size of this preview: 752 × 600 pixelsFull resolution (910 × 726 pixel, file size: 59 KB, MIME type: image/jpeg) Image of Dumbbell Nebula (M27) taken by Robert J. Vanderbei using 10 Ritchey-Chretien telescope and Starlight Express SXV-H9 CCD camera. ... Messier Object 27, the Dumbbell Nebula The Dumbbell Nebula (also known as Messier Object 27, M27, or NGC 6853) is a planetary nebula in the Vulpecula constellation, at a distance of about 1250 light years. ... For other uses, see Astronomy (disambiguation). ... Astronomical objects are significant physical entities, associations or structures which current science has confirmed to exist in space. ... For other uses, see Gas (disambiguation). ... For other uses, see Plasma. ... STAR is an acronym for: Organizations Society of Ticket Agents and Retailers], the self-regulatory body for the entertainment ticket industry in the UK. Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... This article does not cite any references or sources. ... The eight planets and three dwarf planets of the Solar System. ... The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Galaxia Kuklos; or simply the Galaxy) is a barred spiral galaxy in the Local Group, and has special significance to humanity as the location of the solar system, which is located near the Orion...

Planetary nebulae are important objects in astronomy because they play a crucial role in the chemical evolution of the galaxy, returning material to the interstellar medium which has been enriched in heavy elements and other products of nucleosynthesis (such as carbon, nitrogen, oxygen and calcium). In other galaxies, planetary nebulae may be the only objects observable enough to yield useful information about chemical abundances. For other uses, see Chemistry (disambiguation). ... In astrophysics, the questions of galaxy formation and evolution are: How, from a homogeneous universe, did we obtain the very heterogeneous one we live in? How did galaxies form? How do galaxies change over time? A spectacular head-on collision between two galaxies is seen in this NASA Hubble Space... The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ... For other meanings, see heavy metal The term heavy metal may have various more general or more specific meanings. ... Nucleosynthesis is the process of creating new atomic nuclei from preexisting nucleons (protons and neutrons). ...

In recent years, Hubble Space Telescope images have revealed many planetary nebulae to have extremely complex and varied morphologies. About a fifth are roughly spherical, but the majority are not spherically symmetric. The mechanisms which produce such a wide variety of shapes and features are not yet well understood, but binary central stars, stellar winds and magnetic fields may all play a role. The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. ... A sphere is a symmetrical geometrical object. ... For the band of the same name, see: Binary Star (band) Hubble image of the Sirius binary system, in which Sirius B can be clearly distinguished (lower left). ... A solar wind is a stream of particles (mostly high-energy protons ~ 500 keV) which are ejected from the upper atmosphere of a star (in the case of a star other than the Earths Sun, it may be called a stellar wind instead). ... Magnetic field lines shown by iron filings In physics, the space surrounding moving electric charges, changing electric fields and magnetic dipoles contains a magnetic field. ...

Observations

NGC 7293, The Helix Nebula

Planetary nebulae are generally faint objects, and none are visible to the naked eye. The first planetary nebula discovered was the Dumbbell Nebula in the constellation of Vulpecula, observed by Charles Messier in 1764 and listed as M27 in his catalogue of nebulous objects. To early observers with low-resolution telescopes, M27 and subsequently discovered planetary nebulae somewhat resembled the gas giants, and William Herschel, discoverer of Uranus, eventually coined the term 'planetary nebula' for them, although, as we now know, they are very different from planets. Image File history File links Size of this preview: 600 × 600 pixelsFull resolution (3200 × 3200 pixel, file size: 1. ... Image File history File links Size of this preview: 600 × 600 pixelsFull resolution (3200 × 3200 pixel, file size: 1. ... The Helix Nebula (also known as NGC 7293) is a planetary nebula about 650 light-years away in the constellation Aquarius. ... The naked eye is a figure of speech referring to human visual perception that is unaided by enhancing equipment, such as a telescope or binoculars. ... Messier Object 27, the Dumbbell Nebula The Dumbbell Nebula (also known as Messier Object 27, M27, or NGC 6853) is a planetary nebula in the Vulpecula constellation, at a distance of about 1250 light years. ... Vulpecula (IPA: , Latin: ) is a faint northern constellation located in the middle of the Summer Triangle, an asterism consisting of the bright stars Deneb, Vega and Altair. ... Charles Messier Charles Messier (June 26, 1730 – April 12, 1817) was a French astronomer who in 1774 published a catalogue of 45 deep sky objects such as nebulae and star clusters. ... The Messier objects are a set of astronomical objects catalogued by Charles Messier in his catalogue of Nebulae and Star Clusters first published in 1774. ... For other persons named William Herschel, see William Herschel (disambiguation). ... Atmospheric characteristics Atmospheric pressure 120 kPa Hydrogen 83% Helium 15% Methane 1. ...

The nature of planetary nebulae was unknown until the first spectroscopic observations were made in the mid-19th century. William Huggins was one of the earliest astronomers to study the optical spectra of astronomical objects, using a prism to disperse their light. His observations of stars showed that their spectra consisted of a continuum with many dark lines superimposed on them, and he later found that many nebulous objects such as the Andromeda Nebula (as it was then known) had spectra which were quite similar to this – these nebulae were later shown to be galaxies. High resolution spectrum of the Sun showing thousands of elemental absorption lines (fraunhofer lines). ... William Huggins Sir William Huggins, OM , FRS (February 7, 1824 – May 12, 1910) was a British astronomer. ... The visible spectrum is the portion of the optical spectrum (light or electromagnetic spectrum) that is visible to the human eye. ... If a shaft of light entering a prism is sufficiently narrow, a spectrum results. ... Look up continuum in Wiktionary, the free dictionary. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... The Andromeda Galaxy (IPA: , also known as Messier 31, M31, or NGC 224; older texts often called it the Great Andromeda Nebula) is a spiral galaxy approximately 2. ... For other uses, see Galaxy (disambiguation). ...

However, when he looked at the Cat's Eye Nebula, he found a very different spectrum. Rather than a strong continuum with absorption lines superimposed, the Cat's Eye Nebula and other similar objects showed only a small number of emission lines. The brightest of these was at a wavelength of 500.7 nanometres, which did not correspond with a line of any known element.^[1] At first it was hypothesized that the line might be due to an unknown element, which was named nebulium - a similar idea had led to the discovery of helium through analysis of the Sun's spectrum in 1868. The Cats Eye Nebula (NGC 6543) is a planetary nebula in the constellation of Draco. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... A nanometre (American spelling: nanometer, symbol nm) is a unit of length in the metric system, equal to one thousand-millionth of a metre, which is the current SI base unit of length. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Standard atomic weight 4. ... Sol redirects here. ...

NGC 2392, The Eskimo Nebula

However, while helium was isolated on earth soon after its discovery in the spectrum of the sun, nebulium was not. In the early 20th century Henry Norris Russell proposed that rather than being a new element, the line at 500.7 nm was due to a familiar element in unfamiliar conditions. Image File history File links Download high-resolution version (1500x1500, 402 KB)The Eskimo Nebula (NGC 2392) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Download high-resolution version (1500x1500, 402 KB)The Eskimo Nebula (NGC 2392) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... NGC 2392, the Eskimo Nebula. ... Henry Norris Russell (October 25, 1877 – February 18, 1957) was a US astronomer who, along with Ejnar Hertzsprung, developed the Hertzsprung-Russell diagram (1910). ...

Physicists showed in the 1920s that in gas at extremely low densities, electrons can populate excited metastable energy levels in atoms and ions which at higher densities are rapidly de-excited by collisions.^[2] Electron transitions from these levels in oxygen ion (O²⁺ or OIII) give rise to the 500.7 nm line. These spectral lines, which can only be seen in very low density gases, are called forbidden lines. Spectroscopic observations thus showed that nebulae were made of extremely rarefied gas.^[3] For other uses, see Electron (disambiguation). ... Excitation is the amount of energy (energy in a general sense, not energy as defined in physics) that Curtis has. ... Metastability is the ability of a non-equilibrium state to persist for a long period of time. ... A quantum mechanical system can only be in certain states, so that only certain energy levels are possible. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ... A forbidden line is a spectral line emitted by atoms undergoing energy transitions not normally allowed by the selection rules of quantum mechanics. ...

As discussed further below, the central stars of planetary nebulae are very hot. Their luminosity, though, is very low, implying that they must be very small. Only once a star has exhausted all its nuclear fuel can it collapse to such a small size, and so planetary nebulae came to be understood as a final stage of stellar evolution. Spectroscopic observations show that all planetary nebulae are expanding, and so the idea arose that planetary nebulae were caused by a star's outer layers being thrown into space at the end of its life. This article does not cite any references or sources. ...

Towards the end of the 20th century, technological improvements helped to further the study of planetary nebulae. Space telescopes allowed astronomers to study light emitted beyond the visible spectrum which is not detectable from ground-based observatories (because only radio waves and visible light penetrate the earth's atmosphere). Infrared and ultraviolet studies of planetary nebulae allowed much more accurate determinations of nebular temperatures, densities and abundances. CCD technology allowed much fainter spectral lines to be measured accurately than had previously been possible. The Hubble Space Telescope also showed that while many nebulae appear to have simple and regular structures from the ground, the very high optical resolution achievable by a telescope above the Earth's atmosphere reveals extremely complex morphologies. A space observatory is any object in outer space which is used for observation of distant planets, galaxies, and other outer space objects. ... For other uses, see Infrared (disambiguation). ... For other uses, see Ultraviolet (disambiguation). ... For other uses, see Temperature (disambiguation). ... For other uses, see Density (disambiguation). ... Abundance is the state in which there is more than enough. ... A specially developed CCD used for ultraviolet imaging in a wire bonded package. ... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. ... Resolving power is the ability of a microscope or telescope to measure the angular separation of images that are close together. ... “Air” redirects here. ...

Under the Morgan-Keenan spectral classification scheme, planetary nebulae are classified as Type-P, although this notation is seldom used in practice. In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequenly refined in terms of other characteristics. ...

Origins

Computer simulation of the formation of a planetary nebula from a star with a warped disk, showing the complexity which can result from a small initial asymmetry.

Planetary nebulae are the end stage of stellar evolution for most stars. Stars weighing more than a few solar masses will end their lives in a dramatic supernova explosion, but for the medium and low mass stars, such as our Sun, the end involves the creation of a planetary nebula. Image File history File links Download high resolution version (700x980, 68 KB) This image shows a snapshot from a hydrodynamics simulation movie by Vincent Icke at http://www. ... Image File history File links Download high resolution version (700x980, 68 KB) This image shows a snapshot from a hydrodynamics simulation movie by Vincent Icke at http://www. ... In astronomy, stellar evolution is the sequence of radical changes that a star undergoes during its lifetime (the time in which it emits light and heat). ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ...

A typical star weighing less than about twice the mass of the Sun spends most of its lifetime shining as a result of nuclear fusion reactions converting hydrogen to helium in its core. The energy released in the fusion reactions prevents the star from collapsing under its own gravity, and the star is stable. The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Standard atomic weight 4. ...

After several billion years, the star runs out of hydrogen, and there is no longer enough energy flowing out from the core to support the outer layers of the star. The core thus contracts and heats up. Currently the sun's core has a temperature of approximately 15 million K, but when it runs out of hydrogen, the contraction of the core will cause the temperature to rise to about 100 million K. For other uses, see Kelvin (disambiguation). ...

The outer layers of the star expand enormously because of the very high temperature of the core, and become much cooler. The star becomes a red giant. The core continues to contract and heat up, and when its temperature reaches 100 million K, helium nuclei begin to fuse into carbon and oxygen. The resumption of fusion reactions stops the core's contraction. Helium burning soon forms an inert core of carbon and oxygen, with a helium-burning shell surrounding it. According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ... For other uses, see Carbon (disambiguation). ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ...

Helium fusion reactions are extremely temperature sensitive, with reaction rates being proportional to T⁴⁰. This means that just a 2% rise in temperature more than doubles the reaction rate. This makes the star very unstable - a small rise in temperature leads to a rapid rise in reaction rates, which releases a lot of energy, increasing the temperature further. The helium-burning layer rapidly expands and therefore cools, which reduces the reaction rate again. Huge pulsations build up, which eventually become large enough to throw off the whole stellar atmosphere into space.^[4]

The ejected gases form a cloud of material around the now-exposed core of the star. As more and more of the atmosphere moves away from the star, deeper and deeper layers at higher and higher temperatures are exposed. When the exposed surface reaches a temperature of about 30,000K, there are enough ultraviolet photons being emitted to ionise the ejected atmosphere, making it glow. The cloud has then become a planetary nebula. For other uses, see Ultraviolet (disambiguation). ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... Ionisation can be: the process of creating an ion, see ionization a piece of music by Edgar Varèse; see Ionisation (Varèse) This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...

Lifetime

The gases of the planetary nebula drift away from the central star at speeds of a few kilometers per second. At the same time as the gases are expanding, the central star is cooling as it radiates away its energy - fusion reactions have ceased, as the star is not heavy enough to generate the core temperatures required for carbon and oxygen to fuse. Eventually it will cool down so much that it doesn't give off enough ultraviolet radiation to ionise the increasingly distant gas cloud. The star becomes a white dwarf, and the gas cloud recombines, becoming invisible. For a typical planetary nebula, about 10,000 years will pass between its formation and recombination of the star. This article or section does not adequately cite its references or sources. ... Plasma Recombination is a process by which ions of a plasma capture the free energetic electrons to form new neutral atoms. ...

Galactic recyclers

Planetary nebulae play a very important role in galactic evolution. The early universe consisted almost entirely of hydrogen and helium, but stars create heavier elements via nuclear fusion. The gases of planetary nebulae thus contain a large proportion of elements such as carbon, nitrogen and oxygen, and as they expand and merge into the interstellar medium, they enrich it with these heavy elements, collectively known as metals by astronomers. For other uses, see Universe (disambiguation). ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Standard atomic weight 4. ... For other uses, see Carbon (disambiguation). ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ... The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ...

Subsequent generations of stars which form will then have a higher initial content of heavier elements. Even though the heavy elements will still be a very small component of the star, they have a marked effect on its evolution. Stars which formed very early in the universe and contain small quantities of heavy elements are known as Population II stars, while younger stars with higher heavy element content are known as Population I stars (see stellar population). Stars observed in our galaxy appear to group into two general types called Population I and Population II. (A hypothetical third group, Population III, does not occur in our galaxy. ...

Characteristics

Physical characteristics

NGC 6720, The Ring Nebula

A typical planetary nebula is roughly one light year across, and consists of extremely rarefied gas, with a density generally around 1000 particles per cm³. (The Earth's atmosphere, by comparison, contains 2.5×10¹⁹ particles per cm³.) Young planetary nebulae have the highest densities, sometimes as high as 10⁶ particles per cm³. As nebulae age, their expansion causes their density to decrease. Download high resolution version (1024x768, 40 KB) M57, the Ring Nebula Image Credit: NASA and The Hubble Heritage Team (STScI/AURA) [1] Source http://heritage. ... Download high resolution version (1024x768, 40 KB) M57, the Ring Nebula Image Credit: NASA and The Hubble Heritage Team (STScI/AURA) [1] Source http://heritage. ... Planetary Nebula M57 (also known as the Ring Nebula, NGC 6720 or Messier Object 57) is located in the constellation Lyra. ... A light-year or lightyear (symbol: ly) is a unit of measurement of length, specifically the distance light travels in vacuum in one year. ...

Radiation from the central star heats the gases to temperatures of about 10,000 K. Counterintuitively, the gas temperature is often seen to rise at increasing distances from the central star. This is because the more energetic a photon, the less likely it is to be absorbed, and so the less energetic photons tend to be the first to be absorbed. In the outer regions of the nebula, most lower energy photons have already been absorbed, and the high energy photons remaining give rise to higher temperatures. For other uses, see Kelvin (disambiguation). ...

Nebulae may be described as matter bounded or radiation bounded. According to this rather counterintuitive terminology, in the former case, there is not enough matter in the nebula to absorb all the UV photons emitted by the star, and the visible nebula is fully ionized. In the latter case, there are not enough UV photons being emitted by the central star to ionise all the surrounding gas, and an ionization front propagates outward into the circumstellar neutral envelope.

Because most of the gas in a typical planetary nebula is ionised (i.e. a plasma), the effects of magnetic fields can be significant, giving rise to phenomena such as filamentation and plasma instabilities. For other uses, see Plasma. ... Magnetic field lines shown by iron filings In physics, the space surrounding moving electric charges, changing electric fields and magnetic dipoles contains a magnetic field. ... Instability in systems is generally characterized by some of the outputs or internal states growing without bounds. ...

Numbers and distribution

About 3000 planetary nebulae are now known to exist in our galaxy, out of 200 billion stars. Their very short lifetime compared to total stellar lifetime accounts for their rarity. They are found mostly near the plane of the Milky Way, with the greatest concentration near the galactic center. They are only very rarely seen in star clusters, with only one or two known cases. Planetary nebulae have been detected in only four globular clusters: M 15, M 22, NGC 6441 and Palomar 6. For other uses, see Galaxy (disambiguation). ... For other uses, see Milky Way (disambiguation). ... The Galactic Center is the rotational center of the Milky Way galaxy. ... The central square arcminute of M15 imaged using the lucky imaging technique Globular Cluster M15 (also known as Messier Object 15 or NGC 7078) is a globular cluster in the constellation Pegasus. ... Globular Cluster M22 (also known as Messier Object 22, Messier 22, M22, or NGC 6656) is a globular cluster in the Sagittarius constellation. ...

While CCDs have almost entirely superseded photographic film in modern astronomy, a recent high resolution H-alpha survey of the Southern Galactic Plane^[5] permitted searches which have greatly increased the number of known planetary nebulae by ~1000.^[6] The detector was fine grained Kodak Technical Pan film which was used in combination with a very high quality, single element interference filter which isolated the brightest emission line of hydrogen on the wide-field UK Schimdt Telescope. This Balmer line is strongly emitted by almost all planetary nebulae. This article is about motion pictures. ... Eastman Kodak Company (NYSE: EK) is a large multinational public company producing photographic equipment. ... Technical Pan was a black and white film produced by Kodak. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ...

Morphology

Only about 20% of planetary nebulae are spherically symmetric. A wide variety of shapes exist with some very complex forms seen. The reason for the huge variety of shapes is not fully understood, but may be caused by gravitational interactions with companion stars if the central stars are double stars. Another possibility is that planets disrupt the flow of material away from the star as the nebula forms. In January 2005, astronomers announced the first detection of magnetic fields around the central stars of two planetary nebulae, and hypothesised that the fields might be partly or wholly responsible for their remarkable shapes [1]. When two stars are so nearly in the same direction as seen from Earth that they appear to be a single star to the naked eye but may be separated by the use of telescopes, they are referred to as a double star. ... Magnetic field lines shown by iron filings In physics, the space surrounding moving electric charges, changing electric fields and magnetic dipoles contains a magnetic field. ...

Current issues in planetary nebula studies

A long standing problem in the study of planetary nebulae is that in most cases, their distances are very poorly determined. For a very few nearby planetary nebulae, it is possible to determine distances by measuring their expansion parallax: high resolution observations taken several years apart will show the expansion of the nebula perpendicular to the line of sight, while spectroscopic observations of the Doppler shift will reveal the velocity of expansion in the line of sight. Comparing the angular expansion with the derived velocity of expansion will reveal the distance to the nebula.^[7] This does not adequately cite its references or sources. ... The Doppler effect is the apparent change in frequency or wavelength of a wave that is perceived by an observer moving relative to the source of the waves. ...

The issue of how such a diverse range of nebular shapes can be produced is a controversial topic. Broadly, it is believed that interactions between material moving away from the star at different speeds gives rise to most shapes observed. However, some astronomers believe that double central stars must be responsible for at least the more complex and extreme planetary nebulae.^[8] One recent study has found that several planetary nebulae contain strong magnetic fields, something which has been hypothesised by Grigor Gurzadyan already in 1960s (see e.g. ref.[3]). Magnetic interactions with ionised gas could be responsible for shaping at least some planetary nebulae.^[9]

There are two different ways of determining metal abundances in nebulae, which rely on different types of spectral lines, and large discrepancies are sometimes seen between the results derived from the two methods. Some astronomers put this down to the presence of small temperature fluctuations within planetary nebulae; others claim that the discrepancies are too large to be explained by temperature effects, and hypothesise the existence of cold knots containing very little hydrogen to explain the observations. However, no such knots have yet been observed.^[10]

See also

• Asymptotic Giant Branch
• Bipolar nebula
• Interstellar medium
• List of planetary nebulae
• Nebula
• Nova remnant
• Protoplanetary nebula
• Stellar evolution
• Supernova remnant
• White dwarf

A period of Stellar evolution undertaken by all low to intermediate mass stars (0. ... Planetary Nebula M2-9, otherwise known as the Twin Jet Nebula or the Wings of a Butterfly Nebula, is a good example of a bipolar or two-lobed nebula. ... The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ... See also Nebula Planetary nebula Wikipedia Project: Astronomical Objects Categories: | ... The Triangulum Emission Nebula NGC 604 The Pillars of Creation from the Eagle Nebula For other uses, see Nebula (disambiguation). ... A nova remnant is made up of the materials left behind by the gigantic explosion of a star in a nova. ... The Egg Nebula, a protoplanetary nebula in Cygnus A protoplanetary nebula (PPN) is an astronomical object which is formed as a star evolves into a planetary nebula. ... In astronomy, stellar evolution is the sequence of radical changes that a star undergoes during its lifetime (the time in which it emits light and heat). ... The Crab Nebula is an expanding cloud of gas created by the 1054 supernova. ... This article or section does not adequately cite its references or sources. ...

References

1. ^ Huggins W., Miller W.A. (1864). On the Spectra of some of the Nebulae, Philosophical Transactions of the Royal Society of London, 154, 437
2. ^ Bowen, I.S. (1927). The Origin of the Chief Nebular Lines, Publications of the Astronomical Society of the Pacific, 39, 295
3. ^ Gurzadyan, G.A. (1997), The Physics and dynamics of planetary nebulae, Springer; ISBN 978-3-540-60965-0
4. ^ Renzini, A. (1987). Thermal pulses and the formation of planetary nebula shells, Proceedings of the 131st symposium of the IAU, Ed S. Torres-Peimbert, 391
5. ^ Parker, Q.A. et al. (2005). The AAO/UKST SuperCOSMOS H-alpha Survey, MNRAS, 36, 689
6. ^ Parker Q.A, et al. (2006), The Macquarie/AAO/Strasbourg H-alpha Planetary Nebulae Catalogue: MASH, MNRAS, 373, 79
7. ^ Reed, D.S., Balick, B., Hajian, A.R. et al (1999). Hubble Space Telescope Measurements of the Expansion of NGC 6543: Parallax Distance and Nebular Evolution, Astronomical Journal, 118, 2430
8. ^ Soker N. (2002), Why every bipolar planetary nebula is 'unique', Monthly Notices of the Royal Astronomical Society, 330, 481
9. ^ Jordan S, Werner K., O’Toole S.J. (2005), Discovery of magnetic fields in central stars of planetary nebulae, Astronomy & Astrophysics, 432, 273
10. ^ Liu X.W., Storey P, Barlow M.J. et al (2000), NGC 6153: a super-metal-rich planetary nebula?, Monthly Notices of the Royal Astronomical Society, 312, 585

External links

• Entry in the Encyclopedia of Astrobiology, Astronomy, and Spaceflight
• Press release on recent observations of the Cat's Eye Nebula
• Planetary Nebulae, SEDS Messier Pages
• The first detection of magnetic fields in the central stars of four planetary nebulae
• WWW Search for Galactic Planetary Nebulae

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Planetary nebulae

• Planetary Nebulae - Information and amateur observations

   

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