The Sun's Turbulent Outer Layer

An average star in every respect, the Sun is one of 100 billion in our galaxy. Astronomers classify it as a "yellow dwarf," and no dramatic changes are expected for another five billion years or so, when in the last stage of its life, the Sun will transform to a "red giant," expanding into space and gobbling up Mercury, Venus and probably Earth.

At its dense core -- which at about 14 million degrees Kelvin is the furnace for every living room on Earth -- hydrogen atoms fuse to form helium, converting four million tons of matter into energy every second, which radiates outward as light rays. The dense, ionized gas becomes progressively cooler closer to the surface, until at about 30,000 degrees, in the convection zone, electrons join up with protons to form atoms. Here the gas begins to move with a convective motion -- essentially the same as heat circulating in a radiator-heated room. Rising streams of hot gas carry heat toward the Sun's surface where,. at about 5,000 degrees, cooler gas sinks back toward lower reaches of the convective layer. This roiling motion is highly turbulent, and it affects the rate at which energy leaves the Sun, radiating outward into space.

Understanding these flows is important for understanding the evolution of stars, and it has a direct bearing on predictions of solar lifetime. Violent turbulence in the convection zone also affects the periodic flares of gas that shoot out into space, releasing great bursts of energy that can disrupt electronic systems on Earth.

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