Top Ten Nebulas

Top Ten Nebulas

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       A nebula (from Latin: “cloud”) is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, nebula was a general name for any extended astronomical object, including galaxies beyond the Milky Way (some examples of the older usage survive; for example, the Andromeda Galaxy was referred to as the Andromeda Nebula before galaxies were discovered by Edwin Hubble). Nebulae are often 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 massive enough to form stars. The remaining materials are then believed to form planets and other planetary system objects.

  1. Ant Nebula
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    Menzel 3 is a young bipolar planetary nebula in the constellation Norma that is composed of a bright core and four distinct high-velocity outflows that have been named lobes, columns, rays, and chakram. These nebulosities are described as: two spherical bipolar lobes, two outer large filamentary hour-glass shaped columns, two cone shaped rays, and a planar radially expanding, elliptically shaped chakram. Mz 3 is a complex system composed of three nested pairs of bipolar lobes and an equatorial ellipse. Its lobes all share the same axis of symmetry but each have very different morphologies and opening angles. It is an unusual PN in that it is believed, by some researchers, to contain a symbiotic binary at its center. Study suggests that the dense nebular gas at its center may have originated from a source different than that of its extended lobes. The working model to explain this hypothesizes that this PN is composed of a giant companion that caused a central dense gas region to form, and a white dwarf that provides ionizing photons for the PN.
    Links: http://en.wikipedia.org/wiki/Ant_Nebula,
  2. Hourglass Nebula
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    The Engraved Hourglass Nebula (also known as MyCn 18) is a young planetary nebula situated in the southern constellation Musca about 8,000 light-years away from Earth. It was discovered by Annie Jump Cannon and Margaret W. Mayall during their work on an extended Henry Draper Catalogue (1918-1924). At the time, it was designated simply as a small faint planetary nebula. Much improved telescopes and imaging techniques allowed the hourglass shape of the nebula to be discovered by Raghvendra Sahai and John Trauger of the Jet Propulsion Laboratory on January 18, 1996. It is conjectured that MyCn 18’s hourglass shape is produced by the expansion of a fast stellar wind within a slowly expanding cloud which is denser near its equator than its poles. The formation of the shape of the inner “eye” is not yet fully understood. The Hourglass Nebula was photographed by the Wide Field and Planetary Camera 2 of the Hubble Space Telescope. A less-famous “Hourglass Nebula” is located inside the Lagoon Nebula.
    Links: http://en.wikipedia.org/wiki/Hourglass_Nebula,
  3. Cat’s Eye Nebula
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           The Cat’s Eye Nebula (NGC 6543, Caldwell 6) is a planetary nebula in the constellation of Draco. Structurally, it is one of the most complex nebulae known, with high-resolution Hubble Space Telescope observations revealing remarkable structures such as knots, jets, bubbles and sinewy arc-like features. In the center of the Cat’s Eye there is a bright and hot star; around 1,000 years ago this star lost its outer envelope, producing the nebula. It was discovered by William Herschel on February 15th, 1786, and was the first planetary nebula whose spectrum was investigated by the English amateur astronomer William Huggins in 1864. The results of the latter investigation demonstrated for the first time that planetary nebulae consist of hot gases, but not stars. Currently the nebula has been observed across the full electromagnetic spectrum, from far-infrared to X-rays. Modern studies reveal several mysteries. The intricacy of the structure may be caused in part by material ejected from a binary central star, but as yet, there is no direct evidence that the central star has a companion. Also, measurements of chemical abundances reveal a large discrepancy between measurements done by two different methods, the cause of which is uncertain. Hubble Telescope observations revealed a number of faint rings around the Eye, which are spherical shells ejected by the central star in the distant past. The exact mechanism of those ejections, however, is unclear.
    Links: http://en.wikipedia.org/wiki/Cat%27s_Eye_Nebula,
  4. Eskimo Nebula

    The Eskimo Nebula, also known as the Clownface Nebula or Caldwell 39, is a bipolar double-shell planetary nebula. It was discovered by astronomer William Herschel in 1787. The formation resembles a person’s head surrounded by a parka hood. It is surrounded by gas that composed the outer layers of a Sun-like star. The visible inner filaments are ejected by a strong wind of particles from the central star. The outer disk contains unusual light-year long filaments. NGC 2392 lies more than 2,870 light-years away and is visible with a small telescope (but more preferably with a larger telescope) in the constellation of Gemini.
    Links: http://en.wikipedia.org/wiki/Eskimo_nebula,
  5. Crab Nebula
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    The Crab Nebula is a supernova remnant and pulsar wind nebula in the constellation of Taurus. Corresponding to a bright supernova recorded by Chinese astronomers in 1054, the nebula was observed later by English astronomer John Bevis in 1731. At an apparent magnitude of 8.4, comparable to that of the largest moon of Saturn, it is not visible to the naked eye but can be made out using binoculars under favorable conditions. At X-ray and gamma ray energies above 30 keV, the Crab is generally the strongest persistent source in the sky, with measured flux extending to above 10 TeV. Located at a distance of about 6,500 light-years (2 kpc) from Earth, the nebula has a diameter of 11 light years (3.4 pc, corresponding to an apparent diameter of some 7 arc minutes) and expands at a rate of about 1,500 kilometers per second (0.5% c). It is part of the Perseus Arm of the Milky Way galaxy. At the center of the nebula lies the Crab Pulsar, a neutron star 28–30 km across with a spin rate of 30.2 times per second, which emits pulses of radiation from gamma rays to radio waves. The nebula was the first astronomical object identified with a historical supernova explosion. The nebula acts as a source of radiation for studying celestial bodies that occult it. In the 1950’s and 1960’s, the Sun’s corona was mapped from observations of the Crab’s radio waves passing through it, and in 2003, the thickness of the atmosphere of Saturn’s moon Titan was measured as it blocked out X-rays from the nebula.
    Links: http://en.wikipedia.org/wiki/Crab_nebula,
  6. God’s Eye Nebula (Helix Nebula)
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    The Helix Nebula, also known as The Helix, NGC 7293, is a large planetary nebula (PN) located in the constellation Aquarius. Discovered by Karl Ludwig Harding, probably before 1824, this object is one of the closest to the Earth of all the bright planetary nebulae. The estimated distance is about 215 parsecs or 700 light-years. It is similar in appearance to the Cat’s Eye Nebula and the Ring Nebula, whose size, age, and physical characteristics are similar to the Dumbbell Nebula, varying only in its relative proximity and the appearance from the equatorial viewing angle. The Helix Nebula has sometimes been referred to as the “Eye of God” in pop culture.
    Links: http://en.wikipedia.org/wiki/Helix_Nebula,
  7. Eagle Nebula
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           The Eagle Nebula, also known as the Star Queen Nebula, is a young open cluster of stars in the constellation Serpens, discovered by Jean-Philippe de Cheseaux in 1745-46. Its name derives from its shape that is thought to resemble an eagle. It contains several active star-forming gas and dust regions, including the famous “Pillars of Creation,” photographed by the Hubble Space Telescope.
    Links: http://en.wikipedia.org/wiki/Eagle_nebula,
  8. Egg Nebula
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           The Egg Nebula is a bipolar protoplanetary nebula approximately 3,000 light-years away from Earth. Its peculiar properties were first described in 1975 using data from the 11 µm survey obtained with sounding rocket by Air Force Geophysical Laboratory in 1971 to 1974. Before this, the object was catalogued by Fritz Zwicky as a pair of galaxies. The Egg Nebula’s defining feature is the series of bright arcs and circles surrounding the central star. A dense layer of gas and dusts enshrouds the central star, blocking its direct light from our view. However, the light from the central star penetrates the thinner regions of this dusty enclosure, illuminating the outer layers of gas to create the arcs. The dusty enclosure around the central star is very likely a disc. The bipolar outflows in the image indicate that the system has angular momentum, which is very likely generated by an accretion disc. In addition, a disc geometry would account for the varying thickness of the enclosure that allows light to escape along the disc’s axis and illuminate the outer layers of gas, but still blocks it from our direct view along the disc edge. Although dusty discs have been confirmed around several post-AGB objects (S. De Ruyter et al., 2006), a disc around the Egg Nebula is yet to be confirmed. The Egg Nebula was photographed by the Wide Field and Planetary Camera 2 of the NASA/ESA Hubble Space Telescope. The Egg Nebula emits polarized light which can also be detected visually by a medium-sized telescope.
    Links: http://en.wikipedia.org/wiki/Egg_Nebula,
  9. NGC 604
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    NGC 604 is a H II region inside the Triangulum Galaxy. It was discovered by William Herschel on September 11, 1784. It is one of the largest H II regions in the Local Group of galaxies; at the galaxy’s estimated distance of 2.7 million light-years its longest diameter is roughly 1,500 light years (460 parsecs), over 40 times the size of the visible portion of the Orion Nebula. It is over 6,300 times more luminous than the Orion Nebula, and if it were at the same distance it would outshine Venus. Like all emission nebulae, its gas is ionized by a cluster of massive stars at its center, with 200 stars of spectral type O and WR, a mass of 105 solar masses, and an age of 3.5 million years; however, unlike the Large Magellanic Cloud’s Tarantula Nebula central cluster (R136), NGC 604’s one is much less compact and more similar to a large stellar association, being considered the prototypical example of a Scaled OB Association (SOBA).
    Links: http://en.wikipedia.org/wiki/NGC_604,
  10. Great Nebula in Carina
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    The Great Carina Nebula is a large bright nebula that has within its boundaries several related open clusters of stars. Some papers generally refer to this as the Carina Nebula, mostly because of differentiating the many paper published on this object, but the historical precedence as determined by southern observers like James Dunlop and John Herschel, who have both termed it the Eta Argus Nebula or Eta Carinae Nebula. John Herschel also describes “The star η Argus, with the Great nebula about it.” with many of his subsequent published papers supporting this. Eta Carinae and HD 93129A, two of the most massive and luminous stars in our Milky Way galaxy, are among them. The nebula lies at an estimated distance between 6,500 and 10,000 light years from Earth. It appears in the constellation of Carina, and is located in the Carina–Sagittarius Arm. The nebula contains multiple O-type stars. The nebula is one of the largest diffuse nebulae in our skies. Although it is some four times as large and even brighter than the famous Orion Nebula, the Carina Nebula is much less well known, due to its location in the southern sky. It was discovered by Nicolas Louis de Lacaille in 1751–52 from the Cape of Good Hope.
    Links: http://en.wikipedia.org/wiki/Carina_Nebula,
  11. Jellyfish Nebula
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    IC 443 (also known as the Jellyfish Nebula and Sharpless 248 (Sh2-248)) is a Galactic supernova remnant (SNR) in the constellation Gemini. On the plan of the sky, it is located near the star Eta Geminorum. Its distance is roughly 5,000 light years from Earth. IC 443 may be the remains of a supernova that occurred 3,000 – 30,000 years ago. The same supernova event likely created the neutron star CXOU J061705.3+222127, the collapsed remnant of the stellar core. IC 443 is one of the best-studied cases of supernova remnants interacting with surrounding molecular clouds.
    Links: http://en.wikipedia.org/wiki/Jellyfish_nebula,
  12. Tarantula Nebula
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    The Tarantula Nebula is an H II region in the Large Magellanic Cloud. It was originally thought to be a star, but in 1751 Nicolas Louis de Lacaille recognized its nebular nature. The Tarantula Nebula has an apparent magnitude of 8. Considering its distance of about 49 kpc (160,000 light years), this is an extremely luminous non-stellar object. Its luminosity is so great that if it were as close to Earth as the Orion Nebula, the Tarantula Nebula would cast shadows. In fact, it is the most active starburst region known in the Local Group of galaxies. It is also one of the largest such region in the Local Group with an estimated diameter of 200 pc. The nebula resides on the leading edge of the LMC, where ram pressure stripping, and the compression of the interstellar medium likely resulting from this, is at a maximum. At its core lies the compact star cluster R136 (approximate diameter 35 light years) that produces most of the energy that makes the nebula visible. The estimated mass of the cluster is 450,000 solar masses, suggesting it will likely become a globular cluster in the future. In addition to R136, the Tarantula Nebula also contains an older star cluster – catalogued as Hodge 301 – with an age of 20–25 million years. The most massive stars of this cluster have already exploded in supernovae. The closest supernova observed since the invention of the telescope, Supernova 1987A, occurred in the outskirts of the Tarantula Nebula.
    Links: http://en.wikipedia.org/wiki/Tarantula_nebula,
  13. Omega Nebula
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    The Omega Nebula, also known as the Swan Nebula, Checkmark Nebula, Lobster Nebula, and the Horseshoe Nebula (catalogued as Messier 17 or M17 and as NGC 6618) is an H II region in the constellation Sagittarius. It was discovered by Philippe Loys de Chéseaux in 1745. Charles Messier catalogued it in 1764. It is located in the rich starfields of the Sagittarius area of the Milky Way.
    Links: http://en.wikipedia.org/wiki/Swan_nebula,
  14. Stingray Nebula

    The Stingray Nebula (Hen 3-1357) is the youngest known planetary nebula, (Bobrowsky 1994) located in the direction of the southern constellation Ara (the Altar), 18,000 light-years away. Although it is some 130 times the size of our solar system, the Stingray Nebula is only about 1/10 the size of most other known planetary nebulae. Forty years ago it was still a protoplanetary nebula in which the gas had not yet become hot and ionized. In a Nature article, Bobrowsky et al. described how the Hubble observations revealed a 17th-magnitude companion to the Stingray’s 15th-magnitude central star. The image of the Stingray Nebula shown here shows how the outer shells of gas are collimating the continuing outflow of gas from the central star — an important observation, as the process of how these outflows become collimated has not been well understood.
    Links: http://en.wikipedia.org/wiki/Stingray_nebula,
  15. Butterfly Nebulas (Planetary Nebula M2-9 and NGC 6302)
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           Minkowski 2-9, also known as Minkowski’s Butterfly and Twin Jet Nebula, is a planetary nebula that was discovered by Rudolph Minkowski in 1947. It is located about 2,100 light-years away from Earth in the direction of the constellation Ophiuchus. This bipolar nebula takes the peculiar form of twin lobes of material that emanate from a central star. Astronomers have dubbed this object as the Twin Jet Nebula because of the polar jets believed to cause the shape of the lobes. The nebula was imaged by the Hubble Space Telescope in the 1990’s. M2-9 represents the spectacular “last gasp” of a binary star system at the nebula’s center. The primary component of this binary is the hot core of a star that reached the end of its main-sequence life cycle, ejected most of its outer layers and became a red giant, and is now contracting into a white dwarf. It is believed to have been a sun-like star early in its life. The second, smaller star of the binary orbits very closely and may even have been engulfed by the other’s expanding stellar atmosphere with the resulting interaction creating the nebula. Astronomers theorize that the gravity of one star pulls some of the gas from the surface of the other and flings it into a thin, dense disk extending into space. The nebula has inflated dramatically due to a fast stellar wind, blowing out into the surrounding disk and inflating the large, wispy hourglass-shaped wings perpendicular to the disk. Similiarly, NGC 6302 is a bipolar planetary nebula in the constellation Scorpius. The structure in the nebula is among the most complex ever observed in planetary nebulae. The spectrum of NGC 6302 shows that its central star is one of the hottest stars in the galaxy, with a surface temperature in excess of 200,000 K, implying that the star from which it formed must have been very large (cf. PG 1159 star). The central star, a white dwarf, was only recently discovered (Szyszka et al. 2009), using the upgraded Wide Field Camera 3 on board the Hubble Space Telescope. The star has a current mass of around 0.64 solar masses. It is surrounded by a particularly dense equatorial disc composed of gas and dust. This dense disc is postulated to have caused the star’s outflows to form a bipolar structure (Gurzadyan 1997) similar to an hour-glass. This bipolar structure shows many interesting features seen in planetary nebulae such as ionization walls, knots and sharp edges to the lobes.
    Links: http://en.wikipedia.org/wiki/Planetary_Nebula_M2-9, http://en.wikipedia.org/wiki/NGC_6302,
  16. Witch Head Nebula

    IC 2118 (also known as Witch Head Nebula due to its shape), is an extremely faint reflection nebula believed to be an ancient supernova remnant or gas cloud illuminated by nearby supergiant star Rigel in Orion. It lies in the Eridanus constellation, about 900 light-years from Earth. The nature of the dust particles, reflecting blue light better than red, is a factor in giving the Witch Head its blue color. Radio observations show substantial carbon monoxide emission throughout parts of IC 2118 an indicator of the presence of molecular clouds and star formation in the nebula. In fact candidates for pre-main sequence stars and some classic T-Tauri stars have been found deep within the nebula. The molecular clouds of IC 2118 are probably juxtaposed to the outer boundaries of the vast Orion-Eridanus bubble, a giant supershell of molecular hydrogen blown by the high mass stars of the Orion OB1 association. As the supershell expands into the interstellar medium, favorable circumstances for star formation occur. IC 2118 is located in one such area. The windblown appearance and cometary shape of the bright reflection nebula is highly suggestive of a strong association with the high mass luminous stars of Orion OB1. The fact that the heads of the cometary clouds of IC2118 point northeast towards the association is strong support of that relationship.
    Links: http://en.wikipedia.org/wiki/Witch_Head_Nebula,
  17. Hand of God Nebula
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    Description:
    Links:
  18. Calabash Nebula

           The Calabash Nebula, also known as the Rotten Egg Nebula or by its technical name OH 231.84 +4.22, is a protoplanetary nebula (PPN) 1.4 light years (13 Pm) long and located some 5,000 light years (47 Em) from Earth in the constellation Puppis. Violent gas collisions that produced supersonic shock fronts in a dying star are seen in a new, detailed image from NASA’s Hubble Space Telescope. The object is sometimes called the Rotten Egg Nebula because it contains a relatively large amount of sulfur. The densest parts of the nebula are composed of material ejected recently by the central star and accelerated in opposite directions. This material, shown as yellow in the image, is zooming away at speeds up to one and a half million km per hour (one million miles per hour). Most of the star’s original mass is now contained in these bipolar gas structures. A team of Spanish and US astronomers used NASA’s Hubble Space Telescope to study how the gas stream rams into the surrounding material, shown in blue. They believe that such interactions dominate the formation process in planetary nebulae. Due to the high speed of the gas, shock-fronts are formed on impact and heat the surrounding gases. Although computer calculations have predicted the existence and structure of such shocks for some time, previous observations have not been able to prove the theory. This new Hubble image used filters that only let through light from ionized hydrogen and nitrogen atoms. Astronomers were able to distinguish the warmest parts of the gas heated by the violent shocks and found that they form a complex double-bubble shape. The bright yellow-orange colors in the picture show how dense, high-speed gas is flowing from the star, like supersonic speeding bullets ripping through a medium in opposite directions. The central star itself is hidden in the dusty band at the center. Much of the gas flow observed today seems to stem from a sudden acceleration that took place only about 800 years ago. The astronomers believe that 1,000 years from now, the Calabash Nebula will become a fully developed planetary nebula, like a butterfly emerging from its chrysalis.
    Links: Top Ten Butterflies, http://en.wikipedia.org/wiki/Calabash_Nebula,
  19. Orion Molecular Cloud Complex (Horse Head and Flame Nebulas)
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    The Horsehead Nebula is a dark nebula in the constellation Orion. It 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 nebula was first recorded in 1888 by Scottish astronomer Williamina Fleming at the Harvard College Observatory. The Horsehead Nebula is approximately 1,500 light years from Earth. It is one of the most identifiable nebulae because of the shape of its swirling cloud of dark dust and gases, which bears some resemblance to a horse’s head when viewed from Earth. The red or pinkish glow originates from hydrogen gas predominantly behind the nebula, ionized by the nearby bright star Sigma Orionis. The darkness of the Horsehead is caused mostly by thick dust, although the lower part of the Horsehead’s neck casts a shadow to the left. Streams of gas leaving the nebula are funnelled by a strong magnetic field. Bright spots in the Horsehead Nebula’s base are young stars just in the process of forming. The nebula exhibits a noticeable change in the density of the stars which indicates that a red ribbon of radiant red hydrogen gas at the precipice of a sizable dark cloud. The underside of the horse’s visible ‘neck’ reflects this concept of shade and density because it casts a great shadow across the field of view just below the horse’s ‘muzzle.’ The visible heart of the nebula emerges from the gaseous complex to serve as an active site of the formation of “low-mass” stars. A glowing strip of hydrogen gas marks the edge of the massive cloud and noticeable densities of stars are present on either side. The dark cloud of dust and gas is a region in the Orion Nebula where star formation is taking place right now. A complex housing forming stars, known as a stellar nursery, can contain over 100 known organic and inorganic gases as well as dust consisting of large and complex organic molecules. The region of the Orion Nebula containing the Horsehead is a stellar nursery. The darkness of the massive nebula is not explained by this dust and gas, but by the complex blocking the light of stars behind it.
    Links: http://en.wikipedia.org/wiki/Horse_head_nebula,
  20. Cone Nebula
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    The Cone Nebula is an H II region in the constellation of Monoceros. It was discovered by William Herschel on December 26, 1785, at which time he designated it H V.27. The nebula is located about 830 parsecs or 2,700 light-years away from Earth. The Cone Nebula forms part of the nebulosity surrounding the Christmas Tree Cluster. It is in the northern part of Monoceros, just north of the midpoint of a line from Procyon to Betelgeuse. The cone’s shape comes from a dark absorption nebula consisting of cold molecular hydrogen and dust in front of a faint emission nebula containing hydrogen ionized by S Monocerotis, the brightest star of NGC 2264. The faint nebula is approximately 7 light-years long (with an apparent length of 10 arcminutes), and is 2,700 light-years away from Earth. The nebula is part of a much larger star-forming complex. The nebula is sometimes referred to as the Jesus Christ Nebula because of its resemblance to Jesus with his hands in a prayer position.
    Links: http://en.wikipedia.org/wiki/Cone_nebula,
  21. Blinking Nebula
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    NGC 6826 (also known as Caldwell 15) is a planetary nebula located in the constellation Cygnus. It is commonly referred to as the “blinking planetary,” although many other nebulae exhibit such “blinking.” When viewed through a small telescope, the brightness of the central star overwhelms the eye when viewed directly, obscuring the surrounding nebula. However, it can be viewed well in the peripheral vision (averted vision), which causes it to “blink” in and out of view as the observer’s eye wanders. A distinctive feature of this nebula are the two bright patches on either side, which are known as FLIERs, or Fast Low-Ionization Emission Regions. They appear to be relatively young, moving outwards at supersonic speeds. According to Bruce Balick (University of Washington), “some of their observed characteristics suggest that they are like sparks flung outward from the central star late in the very recent past (a thousand years ago). Yet their shapes … seem to suggest that they are stationary, and that material ejected from the star flows past them, scraping gas from their surfaces. Future Hubble observations will monitor any changes in the positions of FLIERs to resolve this issue. In either case, the formation of FLIERs cannot be easily explained by any models of stellar evolution.”
    Links: http://en.wikipedia.org/wiki/Blinking_Nebula,
  22. Orion Nebula
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    The Orion Nebula is a diffuse nebula situated south of Orion’s Belt in the constellation of Orion. It is one of the brightest nebulae, and is visible to the naked eye in the night sky. M42 is located at a distance of 1,344 ± 20 light years and is the closest region of massive star formation to Earth. The M42 nebula is estimated to be 24 light years across. It has a mass of about 2,000 times the mass of the Sun. 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 stars and planetary systems are formed from collapsing clouds of gas and dust. Astronomers have directly observed protoplanetary disks, brown dwarfs, intense and turbulent motions of the gas, and the photo-ionizing effects of massive nearby stars in the nebula.
    Links: http://en.wikipedia.org/wiki/Orion_Nebula,
  23. Owl Nebula
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    The Owl Nebula is a planetary nebula located approximately 2,030 light years away in the constellation Ursa Major. It was discovered by French astronomer Pierre Méchain on February 16, 1781. When William Parsons, 3rd Earl of Rosse observed the nebula in 1848, his hand-drawn illustration resembled an owl’s head and it has been known as such ever since. This 8,000 year old planetary nebula is essentially circular in cross-section with a “relatively bland internal structure.” It was formed from the outflow of material from the stellar wind of the central star as it evolved along the asymptotic giant branch. The nebula is arranged in three concentric shells, with the outermost shell being about 20–30% larger than the inner shell. The owl-like appearance of the nebula is the result of an inner shell that is not circularly symmetric, but instead forms a barrel-like structure aligned at an angle of 45° to the line of sight. The nebula holds about 0.13 times the mass of the Sun worth of matter, including hydrogen, helium, nitrogen, oxygen, and sulfur; all with a density of less than 100 particles per cubic centimeter. Its outer radius is around 0.91 ly (0.28 pc) and it is expanding with velocities in the range of 27–39 km/s into the surrounding interstellar medium. The 14th magnitude central star has since reached the turning point of its evolution where it condenses to form a white dwarf. It has 55–60% of the Sun’s mass, 41–148 times the brightness of the Sun, and an effective temperature of 123,000 K. The star has been successfully resolved by the Spitzer Space Telescope as a point source that does not show the infrared excess characteristic of a circumstellar disk.
    Links: http://en.wikipedia.org/wiki/Owl_nebula,
  24. Red Rectangle
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    The Red Rectangle Nebula, so called because of its red color and unique rectangular shape, is a protoplanetary nebula in the Monoceros constellation. Also known as HD 44179, the nebula was discovered in 1973 during a rocket flight associated with the AFCRL Infrared Sky Survey called Hi Star. The binary system at the center of the nebula was first discovered by Robert Grant Aitken in 1915.
    Links: http://en.wikipedia.org/wiki/Red_Rectangle_Nebula,
  25. Boomerang Nebula *Coolest Natural Place in the Known Universe
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    The Boomerang Nebula is a protoplanetary nebula located 5,000 light-years away from Earth in the constellation Centaurus. The nebula’s temperature is measured at 1 K (−272.15 °C; −457.87 °F) making it the coolest natural place currently known in the Universe. The Boomerang Nebula is believed to be a stellar system evolving toward the planetary nebula phase. It continues to form and develop due to the outflow of gas from its core where a star in its late stage life sheds mass and emits starlight illuminating dust in the nebula. The outflowing gas is moving outwards at a speed of about 164 km/s and expanding rapidly as it moves out into space; this gas expansion results in the nebula’s unusually low temperature. Keith Taylor and Mike Scarrott called it the ‘Boomerang Nebula’ in 1980 after observing it with the Anglo-Australian telescope at the Siding Spring Observatory. Unable to view it with great clarity, the astronomers saw merely a slight asymmetry in the nebula’s lobes suggesting a curved shape like a boomerang. The nebula was photographed in detail by the Hubble Space Telescope in 1998 revealing a more symmetric hourglass shape. In 1995, using the 15-metre Swedish-ESO Submillimetre Telescope in Chile, astronomers revealed that it is the coldest place in the Universe found so far, besides laboratory-created temperatures. With a temperature of −272 °C, it is only 1 °C warmer than absolute zero (the lowest limit for all temperatures). Even the −270 °C background glow from the Big Bang is warmer than the nebula. Aside from the CMB cold spot, it is the only object found so far that has a temperature lower than the background radiation. In 2013, observations of the ALMA radio interferometer revealed other features of the Boomerang Nebula. The visible double lobe of the Boomerang Nebula was observed to be surrounded by a larger spherical volume of cold gas seen only in sub-millimeter radio wavelengths. The nebula’s outer fringes appear to be gradually warming.
    Links: http://en.wikipedia.org/wiki/Boomerang_nebula,
  26. Medusa Nebula
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    The Medusa Nebula is a large planetary nebula in the constellation of Gemini on the Canis Minor border. It also known as Abell 21 and Sharpless 274. It was originally discovered in 1955 by UCLA astronomer George O. Abell, who classified it as an old planetary nebula. The braided serpentine filaments of glowing gas suggests the serpent hair of Medusa found in ancient Greek mythology. Until the early 1970’s, the Medusa was thought to be a supernova remnant. With the computation of expansion velocities and the thermal character of the radio emission, Soviet astronomers in 1971 concluded that it was most likely a planetary nebula. As the nebula is so big, its surface brightness is very low, with surface magnitudes of between +15.99 and +25 reported. Because of this most websites recommend at least an 8-inch (200 mm) telescope with an [O III] filter to find this object although probably possible to image with smaller apertures.
    Links: http://en.wikipedia.org/wiki/Medusa_Nebula,
  27. Links: The Universe, http://en.wikipedia.org/wiki/Nebula,