For decades, scientists have observed that Regulus, the brightest star in the constellation Leo, spins much faster than the sun. But thanks to a powerful new telescopic array, astronomers now know with unprecedented clarity what that means to this massive celestial body.
Regulus and the sun are shown as they would appear side by side. The diameter of Regulus at its equator is 4.2 times that of the sun. The dashed line identifies the spin axis of the star, and the 86 degree tilt of the pole from the north is indicated. The phenomenon of “gravity darkening” is responsible for Regulus being brighter at its poles than around its equator. The picture of Regulus is based upon measurements obtained with the CHARA array, which does not by itself produce a true image of the star.
A group of astronomers, led by Hal McAlister, director of Georgia State Universitys Center for High Angular Resolution Astronomy, have used the centers array of telescopes to detect for the first time Regulus rotationally induced distortions. Scientists have measured the size and shape of the star, the temperature difference between its polar and equatorial regions, and the orientation of its spin axis. The researchers observations of Regulus represent the first scientific output from the CHARA array, which became routinely operational in early 2004.
Most stars rotate sedately about their spin axes, McAlister says. The sun, for example, completes a full rotation in about 24 days, which means its equatorial spin speed is roughly 4,500 miles per hour. Regulus equatorial spin speed is nearly 700,000 miles per hour and its diameter is about five times greater than the suns. Regulus also bulges conspicuously at its equator, a stellar rarity.
Hal McAlister | EurekAlert!
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