Answer: 1)Spiral galaxies are a class of galaxies originally described by astronomer Edwin Hubble in his 1936 work The Realm of the Nebulae.
2) They are part of the Hubble sequence a morphological classification scheme for galaxies.
3) Spiral galaxies usually consist of a rotating disk that contains stars, dust, gas, and a concentration of stars known as the bulge in the center.
4) These bulges are often surrounded by a faint halo of stars, many of which reside in globular clusters – a spherical collection of stars that orbits a galactic core.
5) As such, Spiral galaxies are named after their spiral structures that extend from the center into a galactic disk.
6) They have spiral arms – sites of ongoing star formation that are brighter than the surrounding disk due to the presence of young OB stars that inhabit them.
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