From the August 2006 issue

Bob Berman’s strange universe: Magnetic attraction

August 2006: When we think of cosmic power, magnetism doesn't usually come to mind.
By | Published: August 1, 2006
Bob Berman
When we think of cosmic power, magnetism doesn’t usually come to mind. The Sun’s nuclear furnace churns out blistering heat and blinding light, but magnetism plays no role in the fusion process, which converts our star’s mass to energy. So a star’s magnetic field is like cole slaw: nice but unnecessary. Certainly irrelevant in the energy big leagues. At least, that’s how it always seemed.

Not anymore. During the past few years, researchers have learned that neutron stars — already among the universe’s all-time strangest objects — can be wrapped in magnetic fields brawny enough to affect the rest of the cosmos.

The first hint of magnetic trouble came March 5, 1979, when a burst of gamma rays swept through the solar system at light-speed. Radiation monitors aboard spacecraft near Venus and Earth suddenly went off the scale.

The deadly torrent lasted for only 1/5 of a second, but in that eye blink, some mysterious object had given off twice the energy the Sun has emitted since the pyramids were built. The burst could not be explained by any known phenomenon. Eventually, the culprit was narrowed down to an invisible — to us — neutron star in a neighbor galaxy.

All that power from a tiny neutron star, a dead ex-sun that doesn’t even boast a nuclear generator? Maybe we needed to take another look at these objects.

Neutron stars are tiny — 20 would easily fit within Yellowstone Park. They’re the only stars with a solid surface.

A neutron star forms when a massive star collapses and sends supernova brilliance outward and a tiny remnant core imploding inward. That core — now a 12-mile-wide (19 kilometers) sun — spins crazily, often hundreds of times a second. Such frenzied motion causes its magnetic field to wrap around itself, intensifying the field lines. What’s new about all of this is that for a brief period in a neutron star’s youth, the magnetic field can reach a thousand-trillion gauss. By comparison, Earth’s field is less than 1 gauss. With fields a million-billion times greater than a refrigerator magnet’s, such stars are aptly called magnetars.

Magnetars embody the physics of extremes. Extremes of density, gravity, and magnetism.
More bursts have arrived since that first eye-opener, and altogether a dozen magnetars have now been discovered. Only one, 18,000 light-years away in Cassiopeia, can be seen visually through telescopes. The others are detected solely by the radiation they emit. But more than a million other magnetars are thought to loiter unseen in the dusty hallways of the Milky Way.

I spoke with Vicky Kaspi of McGill University, who won the 2004 Herzberg Medal for her studies of these fantastic objects. She’s obsessed with them.

“Magnetars are the only deep-space objects to directly affect Earth,” she said.

“The [December 27] 2004 burst changed our ionosphere from night to day, and caused a significant drop in ham radio signals. Some fishermen in the arctic saw a sudden aurora at that moment.”

And get this: Magnetars are powered not by nuclear energy like the Sun, nor
by the loss of kinetic energy from rotation slowing, which is what lights up pulsars.

“In a magnetar, we see a unique source of power: All of its energy comes from the gradual loss of its magnetic field,” Kaspi explains. The intense magnetism bends and deforms a magnetar’s solid crust to produce starquakes. They are nothing like the tremors we get here, that can merely destroy a city. No, a neutron star’s ultradense starquakes release titanic bursts of energy that actually create electrons and positrons —
a form of antimatter. When these particles combine, they annihilate each other, and produce the lethal gamma rays that sweep through the universe.

Meanwhile, the magnetism slows the star. In a mere 10,000 years, according to current thinking, the magnetic field will weaken to a paltry 2 trillion times greater than Earth’s. Then, the starquakes stop, the gamma rays die out, and the star may settle down to be a garden-variety neutron star.

In short, magnetars embody the physics of extremes. Extremes of density, gravity, and magnetism. No wonder they’re so much fun to talk about.

As long as we keep our distance.

Imagine a future astronaut approaching a magnetar. At the Moon’s distance from Earth (238,000 miles [383,000 km]), the magnetar would appear as a shapeless point. At half that distance, all the astronaut’s credit cards get mysteriously erased.

He’s now broke, but curiosity drives him forward. At 20,000 miles (32,000 km), the magnetar is still just a dot, but its magnetism now pulls every atom in the astronaut’s body into long, strange, needle formations. By then it’s too late, as he learns that these bizarre objects can truly hold a fatal attraction.