Familiar to inhabitants of the Northern Hemisphere as the Northern Lights, the dancing sheets of excited atmospheric particles called auroras also occur in the Southern Hemisphere. Here they color the Australian sky an eerie red.

Particularly energetic outbursts from the Sun can produce auroral displays over broad regions of the globe.

Sighting the
SUPERENERGETIC

Elsewhere in the cosmos, magnetic fields lace our Milky Way and entire clusters of galaxies. These fields sweep through millions of light-years of space, guiding the motions of vast curtains of charged gas. They also accelerate protons and atomic nuclei that supernova explosions have spewed into space. These particles gain enormous amounts of energy during their looping travels around the galaxy. If they slam into Earth's atmosphere, we call them cosmic rays. Some of them carry so much energy that they have the mass equivalent of a brick. Cosmic rays can damage satellites and computer chips, and they make spurious blips of light on astronomical CCDs. They also account for about 20 percent of the natural radiation that we encounter at Earth's surface.

The most impressive magnetic fields of all may encase the bizarre objects called "magnetars." These neutron stars appear to have magnetic fields 100 times stronger than ordinary neutron stars and a billion times stronger than the strongest fields ever sustained in laboratories on Earth. Such intense fields may crack the exotic surfaces of the dense stars, generating bursts of gamma rays and x-rays that make them visible to us. The crushing force would bring the rapidly spinning stars to a near standstill within thousands of years, a cosmic eyeblink. Once the stars slow down, their radiation would dwindle away. Millions of these quiet objects may populate the Milky Way, utterly invisible to us.

Neutron stars are just a few pinches of stellar mass away from black holes. But the mass of a solitary black hole, as impressive as it is, comes nowhere near that of supermassive black holes, thought to dwell at the hearts of many galaxies. These behemoths may contain hundreds of millions of times more mass than our Sun, all crammed into a volume smaller than our solar system. We call such systems gravitational engines because they use their immense tidal forces to convert (continued)