Physics: Principles and Problems

 

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The Touch of a Distant Star
December 2003

It was 2:00 AM on a cool Seattle morning when a nurse got in her car to drive home after the late shift. The sky was clear and full of stars; as she drove she flipped on her local radio station, letting the music help her begin to wind down after a long day's work.

Suddenly the radio went dead. The nurse looked down at the dashboard. No, the radio itself was still working; the signal had just disappeared. Then, before she could touch the dials, something even stranger happened. A different station began playing--only this one was being broadcast from Omaha.

At the same time, along the east coast, people who were talking to each other on short wave radios experienced a similar moment of silence, only to find themselves abruptly listening to ham radio operators . . . all the way up in Canada!


What On Earth Was Going On?

The answer, it turned out, wasn't "on Earth" at all. This bizarre rearrangement of radio signals, along with other atmospheric effects, was caused by a burst of energy that had just reached our planet from outer space.

Startling as that may sound, these kinds of blasts from space are not uncommon. They come, for example, from our own Sun, and are the result of solar flares. At certain times, known as "solar maximum," the Sun can erupt every few weeks or even every few days, sending X-rays and showers of protons zooming toward Earth. When they get here they collide with our planet's magnetic field and upper atmosphere, causing short wave blackouts and threatening sensitive electronic devices onboard satellites.


A Blast From Space

If you think about it, though, the surge of energy that hit Earth in late 2003, letting that nurse in Washington suddenly hear Nebraska stations, couldn't possibly have come from the Sun. Why? Because it was 2:00AM where she was; that means the blast was hitting the night side of our planet. And that means it came from somewhere in deep space.

Astronomers at NASA, recognizing what had happened, worked on locating the source of the energy wave. Eventually they pinned it down: we had been touched by something called SGR 1900+14, a star over 45,000 light years away. This is such a vast distance that when the blast was initially released, human culture was still in its stone age, and Neandertals roamed the European continent. The energy traveled for all those tens of thousands of years, and only now was it crashing into our planet. While it's dramatic to think that a flare up on the Sun can send a sudden burst of X-rays racing all the way to Earth, it's astounding to think that we could have our atmosphere scorched by something as far away as SGR 1900+14. How could a simple star be that powerful?


The Most Powerful Magnets in the Universe

The answer is that SGR 1900+14 isn't s simple star at all; it's a special class of neutron star called a "magnetar." Magnetars have the strongest magnetic fields of any objects in the universe, and solar flares are caused by disruptions in magnetic fields. To get a sense of how much punch a disruption on a magnetar packs, consider that our own Sun has a magnetic field of about 10 gauss in most spots. (A "gauss" is a unit of measurement for magnetic energy.) An average magnetar weighs in at a million billion gauss. When a magnetar flares, it's an explosion of astounding power.


Just a Matter of Time?

How often does our planet receive a jolt like this from deep space? More often than you might imagine. In the brief time since 1998, ten separate energy waves have passed across our planet, throwing radio transmissions for a loop and causing changes in our upper atmosphere. Five of those events have been linked to SGR 1900+14. The others? We don't yet know. But astronomers think there are more magnetars out there than have been spotted to date. If that's right, it's only a matter of time before they make their presences known . . . with a sudden blast.


Activity
Find a magnet and try picking up some different metal objects from the floor with it. (Don't use aluminum objects--it won't work!) If you can lift an object up, such as a nail, it means your magnet is exerting a stronger force on that nail than the gravitational pull of the entire Earth. How big does the object have to be before Earth's gravity is stronger than your magnet? Have you ever thought of magnetism as being like gravity--one of the forces exerted by stars and planets?

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