While we have all marvelled at the spectacular images of various types of nebulae we have seen on-screen or in magazines, its easy to forget that each image we see represents a brief snapshot of the ongoing cycle of star birth and death across the Universe. After all, diffuse nebulae are not just clouds of gas and dust in space in which stars are born, but another type called planetary nebula are those places created when a star reaches its final evolutionary state, and changes from a red giant to a white dwarf, in the process shedding its outer layers of gas to form a planetary nebula. Although massive stars may instead become neutron stars, over 97% of the stars in our Milky Way will eventually end their lives as a white dwarf, including the Sun.
Which is why we have compiled this list of lesser known, but nevertheless spectacularly beautiful nebulae, that reveals these huge structures in a variety of forms which illustrates the ongoing cycle of star birth and death across the Universe.
Lemon Slice Nebula
– Nebula type: Planetary nebula
– Constellation: Camelopardalis
– Coordinates: RA 12h 33m 06s | Dec. +82° 34’ 00”
– Distance: 4,500 light years
– Diameter: Core: 0.4 light years
– Magnitude: 12.3
-Other designations: IC 3568
Located just 7.5 degrees away from the Pole Star, this is one of the least complex planetary nebulae known, with an almost perfectly spherical morphology. The progenitor star appears to have been an asymptotic red giant, the remains of which can be seen even with modest amateur equipment. This particular star is, however, still heating up, and its current temperature is an estimated 57,000K, at a luminosity of at least 2,000 times that of the Sun. The structure is still very young, which explains the almost total lack of detail or texture in the core, which is expanding at the rate of about 12 km/s or so. The faint halo that surrounds the core region is a shell of dust, while the core consists mostly of ionized helium. The name “Lemon Slice Nebula” derives from a yellow, false color image that originally made the nebula famous.
– Nebula type: Star-forming Pillars & Herbig-Haro Objects with Jets
– Constellation: Carina
– Coordinates: RA 10h 44m 2.38s | Dec. -59° 30′ 29.55″
– Distance: 7,500 light years
– Diameter: Field of view- 1.39 x 1.28 arc minutes
– Age: First observed by Hubble on Feb. 1-2, 2010.
– Other designations: Carina Nebula, HH 901, HH 902
Looking more like the cover of a science fiction novel, this highly enhanced view of a “mountain” of dust and gas in the larger Carina Nebula is the perfect example of a stellar nursery. This image shows the very tip of a pillar of gas and dust (that measures all of three light years from top to bottom), that is being blown apart by the solar winds of nearby stars. However, the assault by hot, energetic stars from outside is deforming the pillar, causing tumultuous internal currents that trigger star formation within the structure. Evidence of this can be seen in the form of the purple jets of light and matter (lower left of the frame) emerging from the dust and gas surrounding such newborn stars.
Monkey Head Nebula
– Nebula type: Emission nebula
– Constellation: Orion
– Coordinates: RA 06h 09.7m | Dec. +20°30′
– Distance: 6,400 light years
– Diameter: 40 degrees
– Magnitude: 6.8
– Other designations: NGC 2174
Located near the star Betelgeuse in the Orion constellation, this nebula is a hive of activity, with new stars forming at a relatively fast pace, and many newborns just starting to emerge from their birth cocoons. The nebula covers an area larger than the full Moon, and while it is visible with binoculars, a small telescope is needed to reveal finer details and texture. This nebula is thought by most investigators to have been created through the process of hierarchical collapse, which is another way of saying that the current structure is the result of a much larger, but more diffuse cloud that had collapsed under its own gravity. This model partially explains the presence of several loose clusters of stars that are embedded within the nebula. However, these clusters will eventually cause the remaining gas and dust to disperse into the surrounding area within the next few million years.
– Nebula type: Planetary nebula
– Constellation: Ara
– Coordinates: RA 17h 16m 21.071s | Dec. -59° 29’ 23.64”
– Distance: 18,000 light years
– Diameter: App. 130 times the diameter of the solar system
– Magnitude: 10.75
– Age: 27 years (First observed by Hubble in 1990)
– Other designations: Hen 3-1357, PN G331
This planetary nebula was only discovered in its present form in 1990, in a position where a pre-planetary nebula was observed in 1971, which makes it the youngest and smallest of all known planetary nebulae. In fact, it was just 25 years ago that it became a visible planetary nebula, a process which usually takes around 100 years, a mere blip compared to millions of years stars exist. The progenitor star was an asymptotic, type B1 supergiant that blew off its outer layers, which are now drifting away from the stellar core. Note that as the nebula drifts away, the stellar remnant heats up, causing the nebula to emit the true, actual colors seen in this image. The color green is emitted by oxygen, blue is emitted by hydrogen, and red is emitted by nitrogen.
Dark Doodad Nebula
– Constellation: Musca
– Coordinates: RA 12h 25m 00s | Dec. -71° 42′ 00?
– Distance: 700 light-years
– Diameter: ˜3 degrees
– Other designations: Sandqvist 149, CG 21, BHR 80, TGU H1875, DCld 301.7-07.2, [DB2002b] G301.70-7.16
The dark Doodad is a very good example of just how opaque dust clouds can be. In this example, the streak of gas and dust near the centre of the frame is dense enough to prevent light from the stars behind it penetrating, creating the appearance of a cleft, or split through the star field in the back ground. The Doodad Nebula is visible from the southern hemisphere with large binoculars, close to the large globular cluster NGC 4372.
– Nebula type: Dark nebula
– Constellation: Crux
– Coordinates: RA 12h 50m | Dec. -62° 30′
– Distance: 600 light years
– Diameter: 30–35 light years (radius)
– Other designations: C99
The Coalsack in Crux represents a different type of dark nebula, in the sense that it is not absolutely dark, since it has a faint glow that is produced by the light of the stars it is obscuring. This nebula is visible to the naked eye and has been known since 1499, when it was discovered by Vicente Yáñez Pinzón. Strangely, even though the Coalsack is the most prominent dark nebula in the southern Milky Way, it is not listed in the NGC or any other catalogue except for the Caldwell Catalogue, in which it is listed as C99.
– Constellation: Leo
– Coordinates: RA 10h 48m 19.0s | Dec. +12° 41′ 21?
– Distance: 38 (± 4.6) × 106 light years
– Diameter: ± 650,000 light years
– Age: App. 1 billion years
While all nebulae are big, the Leo Ring is exceptionally so, even though it is not the biggest known. However, this vast collection of dust and gas is the result of a collision between two huge galaxies, NGC 3384 and M96, which occurred about 1 billion years ago in the heart of the Leo Group of Galaxies. The collision was so violent that roughly a galaxy’s worth of gas (mostly hydrogen and helium) was expelled from both galaxies into intergalactic space, where it eventually settled into the ring structure seen to surround both galaxies today. However, the Leo Ring has since split into two discrete sections, and the parts are now drifted about 38 million light years apart.
– Constellation: Orion
– Coordinates: RA 05h 27.5m | Dec. -03° 58′
– Distance: 518 or 1,434 light years, depending on the source consulted
– Diameter: 10 degrees (600 minutes of arc as seen from Earth)
– Magnitude: 5
– Age: About 2 million years
– Other designations: Sh 2-276
Part of the Orion Molecular Cloud Complex that also contains the Horsehead and Orion Nebulae, Bernard’s’ Loop is thought to have been created by a supernova event that occurred roughly 2 million years or so ago. The structure is also big enough to cover most, if not all of the Orion constellation; consider the relative size of the Orion Nebula roughly in the centre of the Loop for comparison. The supernova that is credited with creating Barnard’s Loop is believed to have occurred in a multi-star system in an explosion that was powerful enough to propel the stars AE Aurigae, Mu Columbae, and 53 Arietis to velocities that place them in the “runaway star” category. Barnard’s Loop is visible without optical aid under dark skies.
Double Helix Nebula
– Nebula type: Emission
– Constellation: Sagittarius
– Distance: 25,000 light-years
– Location: About 300 light years from the galactic centre
This nebula should not be confused with the similarly named Helix Nebula, which is a planetary nebula located in the constellation Aquarius. The Double Helix is so named for the effect that the strong magnetic fields close to the galactic centre have on gaseous material. In this case, the twisting, or rotating magnetic field lines have twisted the material shown here in false color into something resembling a DNA molecule, hence the name, Double Helix Nebula. Only part of this structure has been imaged, with the section shown here about 80 light years in extent. Most of the stars in this structure are only visible in infrared wavelengths, and efforts to image stars that are visible in optical wavelengths are continuing.
– Nebula type: Emission
– Constellation: Cygnus
– Coordinates: RA 20h 12m 7s | Dec. +38° 21.3′
– Distance: 5,000 light years
– Diameter: 18’ × 12’
– Magnitude: 7.4
– Other designations: NGC 6888, Sharpless 105, Caldwell 27
This nebula has a rather complex origin, in the sense that it is being shaped by both the fast solar wind of the Wolf-Rayet star WR 136 (HD 192163) and by the slower moving solar wind from the same star when it evolved into a less energetic red giant star between about 250,000 and 400,000 years ago. The two conflicting solar winds from the same star created two shockwaves moving in opposite directions, with the slower inward-moving shockwave heating the piled-up material to temperatures where it emits X-rays. Even small telescopes of 80-mm aperture will reveal the nebulosity of the structure, while larger instruments fitted with a UHC or OIII filter will sometimes reveal a feature that resembles the Euro currency symbol; hence the nebula’s other name, the “Euro Sign Nebula”.