What are stars made of? Basically, stars are big exploding balls of gas, mostly hydrogen and helium. Our nearest star, the Sun, is so hot that the huge amount of hydrogen is undergoing a constant star-wide nuclear reaction, like in a hydrogen bomb.
In a spiral galaxy like the Milky Way, the stars, gas, and dust are organized into a "bulge," a "disk" containing "spiral arms," and a "halo." Elliptical galaxies have a "bulge-shape" and a "halo," but do not have a "disk.
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