A STAR in the constellation Draco may be giving us a glimpse of the Earth鈥檚
future 4.5 billion years hence, when the Sun swells up into a red giant, say
astrophysicists in Canberra.
If the Sun grows large enough, the Earth鈥檚 atmosphere and surface will be
stripped away. But its iron and nickel core might survive, as the Sun shrinks
back to become a white dwarf star the size of Venus (see 鈥淔inal summer鈥�, New
杏吧原创, 25 July, p 40).
Jianke Li, Lilia Ferrario and Dayal Wickramasinghe of the Australian National
University, think a white dwarf called GD356, 65 light years away, has gone down
a similar path. White dwarfs sometimes have powerful magnetic fields, and Li
says these would induce huge electrical currents in the metal core of any planet
circling the star. The currents would flow between the star and the planet,
carried by the ionised gases surrounding the star.
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The team鈥檚 calculations, due to appear in Astrophysical Journal
Letters, show that such electrical currents could excite hydrogen atoms in
the poles of GD356 to emit frequencies of light which would be polarised by the
star鈥檚 magnetic fields. Until now the polarised light emitted by the star has
defied explanation.
The idea is intriguing, says James Liebert of the University of Arizona in
Tucson, who has studied GD356 since its discovery in the 1980s. 鈥淚 have seen no
viable alternative idea proposed to explain this unique star.鈥�
