, 2 min, 206 words
Tags: physics astrophysics
It's been a while, but here's a new fun physics fact!
The two main means of heat dissipation in stars are radiation, in which light transfers energy away from the center of the star, and convection, in which hotter areas of the star bubble upward, carrying their heat with them and expanding as they rise.
Convection is a much more effective means of heat transfer than radiation, but only kicks in when the stellar temperature decreases outwards with radius more slowly than the convective bubble's temperature as it moves outward (this means that if a bubble of hotter material rises a bit, when it expands and cools, it remains hotter than its surroundings - if it didn't, it would just sink again, and convection wouldn't occur). In this case, convection carries heat outward very quickly, drowning out radiative heat transfer.
Convection occurs in the outer 30% or so of the Sun, and is visible on the surface of the sun as granules (around the size of North America) of bright, hot material rising to the surface surrounded by boundaries of darker, cooler material sinking downward.
Also, according to Wikipedia, just below the surface of the sun are supergranules - convective regions that are larger than the entire Earth!