Artist’s impression of debris around a white dwarf star. Credit: NASA, ESA, STScI, and G. Bacon (STScI).
Artist’s impression of a massive asteroid belt in orbit around a star.
The new work shows that similar rubble around many white dwarfs
contaminates these stars with rocky material and water. Credit: NASA-JPL
/ Caltech / T. Pyle (SSC)
A decades old space mystery has been solved by an international team
of astronomers led by Professor Martin Barstow of the University of
Leicester and President-elect of the Royal Astronomical Society. The
team put forward a new theory for how collapsed stars become polluted –
that points to the ominous fate that awaits planet Earth.
Scientists from the University of Leicester and University of Arizona
investigated hot, young, white dwarfs — the super-dense remains of
Sun-like stars that ran out of fuel and collapsed to about the size of
the Earth. Their research is featured in the journal Monthly Notices of the Royal Astronomical Society, published by Oxford University Press.
It has been known that many hot white dwarfs’ atmospheres, essentially
of pure hydrogen or pure helium, are contaminated by other elements –
like carbon, silicon and iron. What was not known, however, was the
origins of these elements, known in astronomical terms as metals.
“The precise origin of the metals has remained a mystery and extreme
differences in their abundance between stars could not be explained,”
said Professor Barstow, a Pro-Vice-Chancellor at the University of
Leicester whose research was assisted by his daughter Jo, a co-author of
the paper, during a summer work placement in Leicester. She has now
gone on to be an astronomer working in Oxford on extra-solar planets.
“It was believed that this material was “levitated” by the intense
radiation from deeper layers in the star,” said Professor Barstow.
Now the researchers have discovered that many of the stars show signs
of contamination by rocky material, the leftovers from a planetary
system.
The researchers surveyed 89 white dwarfs, using the orbiting Far Ultraviolet Spectroscopic Explorer
telescope to obtain their spectra (dispersing the light by colour) in
which the “fingerprints” of carbon, silicon, phosphorous and sulphur can
be seen, when these elements are present in the atmosphere.
“We found that in stars with polluted atmospheres the ratio of
silicon to carbon matched that seen in rocky material, much higher than
found in stars or interstellar gas.
‘The new work indicates that at around a one-third of all hot white
dwarfs are contaminated in this way, with the debris most likely in the
form of rocky minor planet analogues. This implies that a similar
proportion of stars like our Sun, as well as stars that are a little
more massive like Vega and Fomalhaut, build systems containing
terrestrial planets. This work is a form of celestial archaeology where
we are studying the 'ruins' of rocky planets and/or their building
blocks, following the demise of the main star.
‘The mystery of the composition of these stars is a problem we have
been trying to solve for more than 20 years. It is exciting to realise
that they are swallowing up the leftovers from planetary systems,
perhaps like our own, with the prospect that more detailed follow-up
work will be able to tell us about the composition of rocky planets
orbiting other stars”, said Professor Barstow.
The study also points to the ultimate fate of the Earth billions of
years from now - ending up as merely contamination within the white
dwarf remnant of our Sun.
Science contact
Professor Martin Barstow (available from Wednesday 26 March)
University of Leicester
Tel: +44 (0)116 252 3492
mab@le.ac.uk
Media contacts
Ellen Rudge
News and Events Officer
University of Leicester
Tel: +44 (0)116 229 7467
er134@le.ac.uk
Peter Thorley
Corporate News Officer
University of Leicester
Tel: +44 (0)116 252 2415
pt91@le.ac.uk
Robert Massey
Royal Astronomical Society
Tel: +44 (0)20 7734 3307 / 4582
Mob: +44 (0)794 124 8035
rm@ras.org.uk
Images and captions
Image 1
Artist’s impression of debris around a white dwarf star. Credit: NASA, ESA, STScI, and G. Bacon (STScI)
Artist’s
impression of a massive asteroid belt in orbit around a star. The new
work shows that similar rubble around many white dwarfs contaminates
these stars with rocky material and water. Credit: NASA-JPL / Caltech /
T. Pyle (SSC)
Further information
The new work appears in “Evidence for an external origin of heavy elements in hot DA white dwarfs”,
M. A. Barstow, J. K. Barstow, S. L. Casewell, J. B. Holberg and I.
Hubeny, Monthly Notices of the Royal Astronomical Society, Oxford
University Press, in press.
Notes for editors
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