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Amateur astronomers at the Mount Wilson Observatory in Pasadena, California,
have discovered a star that is posing a problem for the professionals. The
puzzle is that, according to all the normal criteria, the star is older
than the Universe.

In September, six amateurs working under the guidance of Sallie Baliunas
of the Harvard Smithsonian Center for Astrophysics in Cambridge, Massachusetts,
were measuring the light emitted by calcium in nearby stars. A low emission
indicates that the star has a weak magnetic field and, in general, the more
feeble a star’s magnetic field, the older it is.

When Baliunas’s team observed the star HD202537, which is less than
100 light years away, they found its magnetic field to be 30 to 50 per cent
weaker than any Baliunas had ever seen. This corresponds to an age of 19
billion years. Most astronomers believe the Universe to be 10 to 15 billion
years old, so the measurements make the star older than the Universe. ‘Since
that’s ludicrous, this means we have an unusual item on our hands,’ says
Baliunas.

The discovery was an unexpected bonus for the amateurs, who were realising
their ambition to use a large astronomical telescope during the week they
were spending at Mount Wilson through the Smithsonian Research Expedition’s
programme. ‘It was exciting to find something out of context of what’s previously
been detected,’ says Philip Monaghan, one of the participants.

The most likely cause of the discrepancy, according to Baliunas and
her colleague Robert Donahue, is that the star has been misclassified as
a dwarf – a star in its main hydrogen-burning stage, like our Sun. Instead,
it may actually be a red giant, a bright cool star in its later stages.

The calcium emission line of a dwarf is 1 angstrom wide, while a red
giant’s is about 2 angstroms across. If HD202537 is indeed a red giant,
the astronomers would have recorded only half the light emitted by its calcium,
giving the appearance of a very weak magnetic field. But even after widening
the spectral range of their measurement to 2 angstroms, Baliunas and Donahue
say that the star’s magnetic field is still weak.

The definitive test will be to look at the star’s spectrum over a range
of 100 angstroms, in order to reveal other telltale spectral lines that
might show the star to be a red giant.