Published: 20 March 2013

Star researchers demonstrate powerful magnetism

A team of physicists led by Professor Ben Murdin has reproduced the conditions of one of the galaxy’s most hostile environments, where the earthly rules of chemistry don’t apply…

Understanding our universe is no easy task. Black holes, red giants, white dwarfs: these are complex stellar phenomena that tend to be rather resistant to laboratory observation.

In the case of the white dwarf, that hasn’t deterred Professor Ben Murdin and his team in the Department of Physics. Together, they have set about replicating the conditions of a white dwarf on earth. It’s a groundbreaking research project that has already garnered extensive coverage in respected publications like The Economist and Nature.

Dense remnants of stars, with a mass up to eight times that of the Sun, white dwarfs demonstrate extremely high gravitational forces, extreme temperatures and powerful magnetic fields. Replication of their conditions is further complicated by the fact that the rules of chemistry completely change in the stellar environment. Atoms that did not previously stick together can suddenly bond; previously bonded molecules change their size and shape.

Professor Ben Murdin’s team has found that ordinary silicon crystals, like those used in the manufacture of computer chips, are so sensitive to the effects of a magnetic field that they can be used to create white dwarf-like conditions in a lab.

The team wanted to test the impact of the white dwarf’s high-intensity magnetic field on hydrogen emissions. Mimicking these conditions allowed Professor Murdin and colleagues to investigate the response of the electron cloud around a hydrogen atom.

White dwarfs represent the latter stages of life for many stars: one day they will cool down to such an extent that they no longer emit any heat or light. It’s at this point that they will finally become what are known as black dwarfs. For now, they simply plod (relatively speaking) through the Universe, with diminishing means of generating energy, on the final legs of a journey that’s lasted billions of years.

The research itself has serious practical implications. “It’s not just about astronomy,” explains Dr Ellis Bowyer, who ran the experiments. “Learning how to control the shapes of tiny electron clouds in silicon chips allows us design new kinds of computer chips, called quantum computers, where the transistors contain just one atom.”

“The theory predicting the behaviour of hydrogen atoms in magnetic fields this high has been around for just under a century, but until now, no one was able to test it at the limits seen on white dwarfs,” adds co-author Professor Paul Murdin from Cambridge’s Institute of Astronomy.

The team is now looking for signs of a helium molecule – predicted to exist on white dwarf stars, but never before seen.

Read the full published paper in Nature Communications

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