By Ron Cowen
Think of the sun and other giant balls of gas that twinkle in the heavens. Conventional wisdom has it that all these stars are round. But because stars spin, they’re not perfect spheres. The rotation moves material outward more strongly at the equator than at the poles. This nudges the star into a shape reminiscent of that of a toy top.
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For a slow rotator like our sun, the effect is tiny. But for a rapidly rotating star such as Achernar, which is 145 light-years from Earth and six times the sun’s mass, that distortion can be significant. Although astronomers already knew that Achernar spins at least 225 kilometers per second, they were flat-out astonished by their newest observations. The squashed star is more than 1.5 times as wide as it is tall.