Nebula Classification
Created by Captain Aidan Rackham on Wed Apr 15th, 2015 @ 12:44pm
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. |
