Astrophysics (Index)About

spiral arm

(long, winding visible structure within a spiral galaxy)

A spiral galaxy's spiral arm is one of the long structures visible with stars that wind around, forming the spiral. They lead from a central bulge or bar outward toward the edge of the galaxy's disk. They typically host star formation, thus include very bright, early, blue stars, which is what makes them stand out when the galaxy is observed. A grand design spiral galaxy is one with two symmetric spiral arms. Our limited view of the Milky Way (from the inside) has led to challenges in determining its arm structure. It is currently thought to have four major arms. Among the names used:

The Sun resides in a smaller arm called the Orion Arm, Orion-Cygnus Arm, Orion Spur, or Local Arm.


The term spiral arm is also used for spiral-shaped structures of disks such as circumstellar disks. These suggest gravitational instability, which may also be described as a factor in the development of galaxy spiral arms.


(galaxies,spiral)
Further reading:
https://en.wikipedia.org/wiki/Spiral_galaxy#Spiral_arms
https://en.wikipedia.org/wiki/Milky_Way#Spiral_arms
http://burro.cwru.edu/academics/Astr222/Galaxies/Spiral/spiral.html
http://astronomy.swin.edu.au/cosmos/S/spiral+arm

Referenced by pages:
age-velocity-dispersion relation (AVR)
bar
bulge
core collapse supernova (CCSN)
corotation resonance
disk
filament
galaxy classification
Gould's Belt
grand design spiral galaxy
lenticular galaxy (S0)
Lindblad resonance
Milky Way (MW)
open cluster (OC)
peculiar galaxy (p)
Population I (Pop I)
Population II (Pop II)
Radcliffe wave
Scutum-Centaurus Arm
spiral galaxy
stellar population
tidal arm

Index