Death from the Skies! by Ph. D. Philip Plait Read Free Book Online Page A

come.
    Some people like to say the Sun is essentially a giant nuclear bomb, but that’s misleading: a bomb explodes. 7 But the Sun doesn’t explode, because it has a lot of mass. This means it has a lot of gravity, which balances the energy it generates. The heat produced makes the Sun want to expand (like a hot-air balloon expands), but the Sun’s own gravity holds it together. It’s a balancing act; in fact, a good definition of a star is a ball of gas with nuclear fusion in its center held together by its own gravity.
    But just because the entire Sun doesn’t explode like a bomb doesn’t mean that explosions don’t happen. In fact, the Sun is capable of epic eruptions; but they’re not nuclear in nature, they’re magnetic.

CURRENT EVENTS
    When I was a kid (and sure, I’ll admit it: even today), I was fascinated by magnets. I had a few different kinds, and I would play with them constantly. I read a lot about magnetism, and in one of my books it said magnetism could be destroyed by heat. I (carefully!) held a bar magnet in a candle flame for a few minutes, and sure enough, after that it wouldn’t attract nails or needles anymore.
    I was also something of an astronomy geek even then, and I had a book that talked about the magnetic field of the Sun. I remember being confused by this: how could the Sun have a magnetic field if it was so hot?
    What I didn’t understand is that there is more than one way to create a magnetic field. Simply put, a magnetic field can be generated by moving electrical charges. When you turn on a light, for example, electrons (subatomic particles with a negative charge) flow through a wire from the wall to the light. This motion produces a local (temporary) magnetic field around the wire. When you turn off the light, though, the flow of electrons stops, and the magnetic field collapses. 8
    This has a very interesting—and useful—effect. If an electrically conductive object like a wire moves through a magnetic field, an electric current will flow along the wire. This current, in turn, generates its own magnetic field. If the current moves in just the right way, its magnetic field will reinforce the magnetic field already there and you get a self-sustaining system.
    However, this only works if there is an outside source of energy to make things move. For example, you could use a crank to make a coil of copper wires rotate inside a magnetic field (generated by a permanent magnet). Your arm supplies the outside energy. Or, if you’re smart, and you want to make a lot of electricity, you stick this getup near a source of flowing water—say, inside a dam—and make giant turbines composed of copper that spin as water flows past them . . . which is precisely how hydroelectric power plants work. A system that converts mechanical energy to electromagnetism in this way is called a dynamo.
    The Sun is just such a dynamo. Its interior is hot: so hot, in fact, that electrons are stripped off their atoms, allowing them to flow more or less freely. An atom that is missing one or more electrons is said to be ionized. As these electrons move in the ionized gas, they generate magnetic fields.
    If the Sun were just sitting there in space, a nonmoving and non-rotating ball of hot gas, the electrons inside would move around higgledy-piggledy, and all those individual magnetic fields generated would be oriented in random directions and cancel each other out. But the motions of the electrons in the Sun are far from random. For one thing, the Sun spins on its axis once a month, and that can create streams of gas in its interior. This preferred direction of motion for the electrons means that their individual magnetic fields can build on one another like creeks all flowing into a river, creating a larger magnetic field.
    If it were just that simple, scientists would understand everything about how the Sun works. But in reality the Sun is incredibly complicated, with a vast system of moving gas inside it. The