Soon thereafter, gravity will win out and compress the stellar core to higher temperatures. Eventually the core becomes a white dwarf . These high temperatures somehow cause the expulsion of star's outer layers, creating a planetary nebula such as the Blue Snowball pictured above. Although the Blue Snowball, also known as NGC 7662, does appear blue, the above picture's colors are not real and were chosen to highlight the emission of certain ions in the nebula. Many things are still not known about planetary nebula , including details of the physical mechanism that creates the nebula, and the reason for fast knots of gas in the outer regions known as fliers .
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