Scientists solve riddle of celestial archaeology

Mar 26, 2014
This is an artist's impression of debris around a white dwarf star. Credit: NASA, ESA, STScI, and G. Bacon (STScI)

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.

Scientists from the University of Leicester and University of Arizona investigated hot, young, —the super-dense remains of Sun-like that ran out of fuel and collapsed to about the size of the Earth. Their research is featured in MNRAS- the 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 , the left overs from a planetary system.

This is an artist's impression of a massive asteroid belt in orbit around a star. The new work with SDSS data shows that similar rubble around many white dwarfs contaminates these stars with rocky material and water. Credit: NASA-JPL / Caltech / T. Pyle (SSC)

The researchers surveyed 89 white dwarfs, using the Far Ultraviolet Spectroscopic Explorer 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 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 left overs 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 a contamination within the white dwarf Sun.

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More 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.

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not rated yet Mar 26, 2014
"In the end, gravity always wins." Even around dying stars...
1 / 5 (3) Mar 26, 2014
Great speculation on the extrapolated terminal fate of the earth, not exactly scientific, but with equal credibility as the unknowable Big Bang or the Beginning at infinity past.
5 / 5 (1) Mar 27, 2014
Planetary fossils.

@hrfJC: What is your evidence that such an extrapolation is unscientific?

Both the fates of stars the Sun's size and of inner planets like Earth is modeled ("extrapolated") and then tested as here. That is the very definition of the core of science, testability and repeatability. So at least superficially it looks like usual science. (You have to check the constraints and the statistics to really know, of course.)

"Big Bang" is not "unknowable" or infinite in age, in fact Planck showed 2013 (by releasing some preliminary polarization data) that it is the only remaining theory that predicts all features of the cosmic microwave background and that the observable universe is 13.8 years old. So again, this is testable.

It is inflation, the preceding part, that is still up for grabs. (See the BICEP2 results lately.) If inflation is a fact, we do not know how old the inflation universe is that later seeded the observable universe at a spacetime size of ~ proton.
not rated yet Mar 27, 2014
[cont] Maybe we can test it, but it is iffy. Linde's chaotic inflation looks best at the current time, and such an inflaton undergoes a 10^10^13 expansion before it seeds the first universe. But it then goes on, meaning that it generates an eternal fractal.

Worse, as Linde points out, if a seed spacetime fluctuated into inflation once, it should happen again as no process in physics generates lone systems. So there are fractals of fractals, eternally going back unless other constraints appears.

And such fractals lose their memory fast. So with likelihood = 1 every universe will find itself later than the roots, if it can be measured. So while it is untestable as of yet, the inflationary fractal is effectively eternally old. If ... if ... if. But as of yet, not non-scientific, we can't yet exclude that it is testable.
1 / 5 (1) Mar 29, 2014
Kind of hard for god to fake this one without suspicion, eh Lrrkrr?

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