Answer to Question #173619 in Astronomy | Astrophysics for ANJU JAYACHANDRAN

Question

4. a) Explain Hubble’s scheme of galaxy classification with the help of a diagram.

Describe the prominent features of spiral galaxies.

Answer 1

Let us look at the Hubble's classification scheme (from en.wikipedia.org).

There are elliptic galaxies (from E0 to E7 or from spherical to highly elliptic), lenticular galaxies (S0, disk galaxies without prominent spiral arms) and spiral galaxies (S and SB). Here are two types of the spiral galaxies. Sa, Sb, Sc are the spiral galaxies without the central bar and SBa, SBb, SBc types have a central bar. The spiral galaxies always have the spiral arms at their disks. Sa and SBa types have tight spiral arms, Sc and SBc have very untight spiral arms. We may also see that spiral galaxies have bulges (central spheroids), the largest and most prominent bulges are in Sa and SBa types.