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AT LAST, astrophysicists will be able to do something most scientists take
for granted鈥攅xperiments. They may be able to generate magnetic fields as
intense as those in the hearts of galaxies, using only a laser and a thin
wire.

Astrophysics deals with the behaviour of weird objects such as white dwarfs,
collapsing stars and quasars, which have magnetic fields billions of times
stronger than Earth鈥檚. But astrophysicists can鈥檛 test their theories about the
way matter in these fields behaves because the most powerful artificial magnetic
fields are at least a thousand times weaker.

That could now change, because Alexander Kaplan at Johns Hopkins University
in Baltimore and Peter Shkolnikov at the State University of New York at Stony
Brook claim existing lasers could create huge magnetic fields, as well as
ultrafast radiation pulses, simply by propelling electrons round in a
circle.

Pulse lasers emit circularly polarised light, meaning that the
electromagnetic field of the light rotates. Any electron within the field is
pushed round in a circle as well, causing it to send a narrow beam of X-rays or
gamma rays out in front of it like a revolving lighthouse beam.

Kaplan and Shkolnikov say that if the laser were fired at a thin wire, the
electrons in the wire would rotate in synchrony, making the wire radiate like an
antenna (see Graphic). Interference would destroy the radiation in all
directions but two, leaving two pulsing beams at right angles to the direction
of the laser and the wire.

The researchers call their antenna a 鈥渓asetron鈥�. The radiation pulses it
gives out would be millions of times briefer than those of the laser powering
it. Top-of-the-range lasers that pulse every picosecond鈥�10^-12 of a
second鈥攃ould produce radiation bursts just zeptoseconds
濒辞苍驳鈥�10^-21 of a second. That鈥檚 swift enough to image even
fast-moving atomic nuclei.

But the most obvious application of the lasetron is to use the huge magnetic
field produced by so many electrons circling in synchrony. Shkolnikov says that
with today鈥檚 lasers, the technique could generate a field of 1 million
teslas鈥攁t least as strong as that around a white dwarf star. If you
powered the lasetron with laser radiation of centimetre wavelengths, the
magnetic field formed around the wire would be stable for several centimetres
around the wire鈥攅nough to do experiments within it.

The lasetron would allow astrophysicists to test their ideas about what
happens to matter in such powerful magnetic fields. Atoms should become
elongated as the field stretches their orbiting electrons, but no one yet knows
how this would affect molecular reactions. 鈥淭his is a way to do astrophysics on
a tabletop,鈥� says Shkolnikov.