Nebula Classification

Created by Lieutenant Commander Alexander Gunning on Mon May 4th, 2015 @ 2:07pm

What Is a Nebula?
A nebula (from Latin: "cloud" [1]; pl. nebulae or nebul, with ligature or nebulas) is an interstellar cloud of dust, hydrogen gas, helium gas and plasma. 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 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 planetary system objects.

Nebula Class A - Emission Nebula

Composition Hydrogen, helium, oxygen
Average Size 100 - 5,000 ly
Average Temp. 10 - 20 K
Lifespan 1 - 2 million years
Color Red, green, blue
Example Lagoon Nebula, Veil Nebula
Emission nebulas are large clouds of ionized plasma where star formation usually takes place. They are illuminated from within by groups of young stars that form in H II Regions within the nebula.

Nebula Class B H II Region

Composition Hydrogen, helium
Average Size 20 - 2,000 ly
Average Temp. 10,000 K
Lifespan 1 - 2 million years
Color Red, pink
Example Eagle Nebula
An H II region is a large stellar nursery, typically located inside an emission nebula. Over the duration of its lifespan, an H II region can give birth to thousands of stars. Gravimetric forces by the larger stars will eventually disperse the nebula and leave behind a star cluster similar to the Pleiades.

Nebula Class C Bok Globule

Composition Hydrogen, helium, carbon
Average Size 1 ly
Average Temp. 3 K
Lifespan 1 - 2 million years
Color Black
Example NGC 281, NGC 1999, BHR 71
An H II region is a large stellar nursery, typically located inside an emission nebula. Over the duration of its lifespan, an H II region can give birth to thousands of stars. Gravimetric forces by the larger stars will eventually disperse the nebula and leave behind a star cluster similar to the Pleiades.

Nebula Class D Reflection Nebula

Composition Hydrogen, carbon, iron, nickel
Average Size 100 ly
Average Temp. 25,000 K
Lifespan 10 million - 10 billion years
Color Blue, purple
Example Trifid Nebula, Witchhead Nebula
Reflection nebulas are large clouds of dust that reflect light from nearby stars. The nearby stars are not usually hot enough to cause ionization, but are bright enough to make the dust visible. Star formation can occur within a reflection nebula.

Nebula Class E Planetary Nebula

Composition Carbon,oxygen,nitrogen,calcium
Average Size 1 ly
Average Temp. 10,000 K
Lifespan 10,000 years
Color Orange, green, blue
Example Ring Nebula, Hourglass Nebula
Despite the name, planetary nebulas have nothing to do with planets. They are, in fact, the final stage of life for most stars, developing when a star is no longer able to sustain nuclear fusion. As the star's core contracts, it ejects ionized gases into space, creating a planetary nebula. This plays a crucial role in the evolution of the galaxy, for the process returns material to the interstellar medium.

Nebula Class F Dark Nebula

Composition Hydrogen
Average Size 200 ly
Average Temp. 7 K
Lifespan 1 - 2 million years
Color Black
Example Coalsack Nebula, Snake Nebula
Dark nebulas are a type of large molecular cloud. The cloud cores are completely invisible to the naked eye, and are be undetectable aside from microwave emissions from the molecules within. Dark nebulas have strong magnetic fields that create considerable gravimetric forces in and around the nebula. Stars and astrophysical masers can form deep inside dark nebulas.

Nebula Class G Supernova Remnant

Composition Ionized hydrogen, oxygen
Average Size 3 ly
Average Temp. 10,000,000 K
Lifespan 1,000,000 years
Color Varies; typically orange, blue
Example Tycho's Remnant,1987A
When a massive star reaches the end of its life, it explodes in an immensely powerful supernova. This event blows the entire star apart, leaving in its wake a remnant nebula that expands into the interstellar medium.

Nebula Class H Nova Remnant

Composition Ionized hydrogen, oxygen
Average Size .5 ly
Average Temp. 5,000 K
Lifespan 300 years
Color Varies; typically blue, orange
Example RR Pictoris
Nova remnants are similar to supernova remnants, only much smaller on all levels. They are also much more common.

Nebula Class I Solar Nebula

Composition Hydrogen, helium, oxygen
Average Size 100 AU
Average Temp. 150 K
Lifespan 2,000,000 years
Color Yellow, orange
Example Panak
While most stars form within emission nebulas, there are exceptions to the rule. When a young star forms elsewhere, gravimetric forces gradually attract a disk of dust and gas that flatten to form a new star system that includes planets and asteroids.

Nebula Class J Wolf-Rayet Nebula

Composition Helium, carbon, oxygen
Average Size .5 ly
Average Temp. 25,000 - 50,000 K
Lifespan 1 - 2 million years
Color Blue
Example NGC 6888, NGC 3199
A Wolf-Rayet nebula forms when strong stellar winds cause a Class O star to rapidly lose its mass. The dispersed mass forms a nebulous halo around the star.

Nebula Class K Inversion Nebula

Composition Ionized plasma strings
Average Size 200 AU
Average Temp. 10,000 K
Lifespan 5 - 10 years
Color Pink
Example Marayna's Nebula
Inversion nebulas are rare, highly unstable nebulas created by plasma strings. They typically burn out after a few years.


Categories: Stellar Cartography