ASTRON 1F03 Quiz: Normal and Active Galaxies
12 Apr 2016
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Document Summary
Spiral galaxies are classified according to the size of their central bulge. Sa tends to have the most tightly bound spiral arms, with types sb and sc progressively less tight, although the correlation is not perfect. Similar to the spiral galaxies are the barred spirals. Elliptical galaxies have no spiral arms and no significant disk. They come fin many sizes, from giants ellipticals of trillions of stars, down to dwarf ellipticals of fewer than a million stars. Ellipticals also contain very little, if any, cool gas and dust, and show no evidence of ongoing star formation. Many, however have large clouds of hot gas extending far beyond the visible boundaries of the galaxy. Ellipticals are classified according to their shape, from e0 (almost spherical) to e7 (the most elongated). S0 (lenticular) and sb0 galaxies have a disk and bugle but no spiral arms and no interstellar gas. Irregular galaxies have a wide variety of shapes.
