Sa & SBa: The "Early" Spiral Galaxies
Spirals galaxies have extended disks or arms. They progress from very bulge-dominated spirals, to arm-dominated spirals. Below are two kinds of bulge-dominated spirals: one with a normal bulge and one with a bar. Their designations are, respectively Sa and SBa.
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M94 is an Sa galaxy. Its arms are dwarfed by the immense central bulge. What you can clearly see in this photo is the dust lanes. This tells us that gas and dust exist in the outer disk region of the galaxy. Sa galaxies have some star formation occurring. |
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M65 is a weak example of a barred spiral, SBa. It's bulge almost looks square! This hint of elongation along the bulge is referred to as a bar. Bars can be a bit more difficult to see in early spirals because of their large stellar bulge. |