Stellar magnetic field

Article By:

Valenti, Jeff A. Space Telescope Science Institute, Baltimore, Maryland.

Last reviewed:January 2021

DOI:https://doi.org/10.1036/1097-8542.654100

A magnetic field, far stronger than the Earth's magnetic field, which is possessed by many stars. Magnetic fields are important throughout the life cycle of a star. Initially, magnetic fields regulate how quickly interstellar clouds collapse into protostars. Later in the star formation process, circumstellar disk material flows along magnetic field lines, either accreting onto the star or flowing rapidly out along the rotation axis. Outflowing material (stellar winds) carries away angular momentum, slowing rotation at a rate that depends on stellar magnetic field strength. On the Sun, dark sunspots, prominences, flares, and other forms of surface activity are seen in regions where there are strong magnetic fields. There is some evidence that long-term variations in solar activity may affect the Earth's climate. Turbulence in the solar atmosphere drives magnetic waves which heat a tenuous corona (seen during eclipses) to millions of degrees. About 10% of hotter stars (with temperatures of about 10,000 K) with stable atmospheres are Ap stars, which have stronger magnetic fields that control the surface distribution of exotic elements. Even after stars end their internal fusion cycle and become compact remnants, magnetic fields channel accreting material from binary companions, occasionally producing spectacular novae. Despite the enormous gravity around pulsars, magnetic forces far exceed gravitational forces, creating intense electromagnetic beams that spin down (slow the rotation of) the pulsar. See also: Binary star; Cataclysmic variable; Nova; Protostar; Pulsar; Stellar evolution

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