PHYS 1010 Chapter Notes - Chapter 15: Quasar, Planetary Nebula, Recessional Velocity
23 Apr 2016
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Edwin hubble was the first person to categorize galaxies and we still use the hubble classification scheme today. Spiral galaxies are classified according to the size of their central bulge. Type sa has the largest central bulge, type sb is smaller, and sc is the smallest. Type sa tends to have the most tightly bound spiral arms, with types sb and sc progressively less tight, although the correlation is not perfect. Type sc galaxies have the most interstellar gas and dust and sa have the least. The components of spiral galaxies are the same as in our own galaxy: disk, core, halo, bulge, spiral arms. Similar to the spiral galaxies are the barred spirals. They have a bar" of stellar and interstellar matter that extends beyond the bulge into the disk. Referred to as sba, sbb and sbc; they share the properties of regular spirals. Elliptical galaxies have no spiral arms and no disk.
