The Sciences

The Universe's Most Powerful Magnets

Nuclear fusion reactors, particle colliders, and other big-science rely on giant magnetic fields. But nature's most powerful magnets blow even our best efforts away.

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Photo Credits: All text by Andrew Moseman; image: NASA

Magnets do a lot more than stick on your refrigerator. The strongest manmade fields make particle collider and fusion reactions possible. But, as we shall see, our best efforts pale in comparison to magnetic fields in the far reaches of the universe, like those emanating from neutron stars.

Different kinds of supernovae produce different results. The largest supernovae leave black holes in their wake, but slightly less massive ones create neutron stars. These stars are incredibly dense, and incredibly magnetic: While the Earth lackadasically maintains a magnetic field of about 0.5 gauss, a neutron star's field measures in the trillions. This one is Cassiopeia A, imaged by the Chandra X-Ray observatory.

Photo Credits: Image: NASA

Not all neutron stars are created equal. Some, for reasons that are not totally understood, fall under the classification of "magnetars," which take the already-astounding field of an ordinary neutron star and multiply it by about 1,000 times. Even parked halfway between the Earth and the moon, a magnetar could still strip the info from your credit card.

Scientists aren't sure why magnetars are so much stronger than ordinary neutrons stars, but astronomers are finding more of them all the time. When the extraordinary magnetic field begins to slow the star's spinning, it releases intense bursts of energy in X-ray wavelengths, visible to NASA's X-ray observatories.

Photo Credits: Image: NASA/CXC/M. Weiss

We know the story of black holes: These ultra-dense supernova remnants exert such a fearsome gravitational pull that they suck in everything in their neighborhood (within the "event horizon"), further fueling the black hole. But the story doesn't end with gravity. Once matter is pulled toward the black hole, it rotates around the edge and spins off some of its angular momentum before it falls in.

That's where magnetism comes in. As gasses spin in a disk on the black hole's edge, they create their own magnetic field, which ejects some of the gas at the disk's exterior away from the black hole. That ejection steals momentum from the inside of the gas disk that's closest to the black hole. The gas then slows down and falls into the dark monster.

Photo Credits: Image: Leroy N. Sanchez/LANL

While man-made magnets can't hold a candle to the most powerful magnets in nature, our best efforts are nothing to sneeze at. Three locations in the United States--Florida State University, the University of Florida, and the Los Alamos National Laboratory in New Mexico--compose the National Magnetic Field Laboratory, home to the biggest man-made magnets in the world. Los Alamos alone houses eight magnets capable of operating at 50 tesla or more (a regular bar magnet generating about .01 tesla), including the 100-tesla multiple shot magnet that took ten years to create.

Running all those magnets isn't cheap: Los Alamos uses a 1.43 gigawatt generator and five 64-megawatt power supplies. The generator sits on a bed of 60 springs, which are necessary to ease the tremors created when it decelerates after powering the magnet, creating an earth-shaking fury.

Photo Credits: Image: CERN

The LHC is a huge machine bearing huge magnets, with coils that are 14 meters or more in length. The superconducting magnets, operating in excess of eight tesla, will propel the protons around the 17-mile ring before they smash into one another and create a cascade of subatomic particles.

All this it will do... we hope. The LHC barely got going last September before bad electrical connections in the magnet's cooling systems shut the experiments down. Now, nearly a year later, everyone's favorite supercollider is still offline and will be until at least November, if not longer.

Photo Credits: Image: ITER

Contained, self-sustaining fusion power is still a dream, but the reason that dream may be attainable is magnetism. The International Thermonuclear Experimental Reactor (ITER) is a multinational collaboration that represents one of the world's largest attempts to fuse deuterium and tritium, two heavy isotopes of hydrogen.

When (or if) ITER is built, it will heat up the fusion materials into a plasma state, generating 500 megawatts of heat. The machine will then use magnetic field to contain and control that superheated plasma mass.

Photo Credits: Image: Nijmegen High Field Magnet Laboratory

Superconductivity is one of those bizarre phenomena that classical physics alone can't totally explain. Some materials, when cooled to temperatures near absolute zero, reach zero electrical resistance. Thus, an electric current can persist indefinitely.

Scientists use superconductive materials in particle colliders like the LHC, but you don't have to go all the way to Europe to do entertaining tricks with them. The persistent current in a superconductor can levitate materials, since the constant current repels the magnetic field of the levitating object, even a living one. Here, Dutch scientists levitate a frog in a 16-tesla magnetic field.

Photo Credits: Image: Roberta Dupuis-Devlin/UIC Photo Services

Since scientists created the first magnetic resonance images (MRIs) in the early 1970s, the technology has grown more powerful by leaps and bounds--so much so that the Food and Drug Administration has capped the level of magnetism to which humans can be exposed. Eight tesla was the maximum in 2003, until University of Illinois at Chicago scientists rolled out a 9.4 T scanner, which eventually gained FDA approval.

But that's not the world's most powerful MRI. Bruker BioSpin, who built a 9.4 T scanner for MIT, upped the ante and designed an 11.7 T MRI scanner. In 2009, the University of Texas announced plans to install an 11.7 T MRI scanner in its health center.

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