The Stars That Shouldn’t Exist

Theories in astronomy are fun to model on paper with equations, but once in awhile they need to stand up to observations.  Phil Berardelli wrote for Science Now:

It seems as though every time astronomers point their telescopes at the night sky, some weird new finding forces them to revamp their theories.  And so it is with nine newly discovered white dwarfs.  The stars defy their expected chemical makeup and by rights shouldn’t even exist.  An explanation could open up a new branch of astronomy.

The stars may be violating human rights but apparently abide by stellar rights.  One astronomer concluded, “It tells us that nature has found a way that we didn’t know to make white dwarf stars without the usual hydrogen or helium surface layers.”
    According to stellar evolution theory, white dwarfs should be enveloped with hydrogen and helium, not carbon.  Astronomers could find no trace of hydrogen or helium in the spectra from these oddball stars.  “Astronomers don’t have a clue why,” the article continued.  Another astronomer commented, “There is currently no explanation how such stars can be formed.  It’s a real challenge to stellar-evolution theory.”  The stars were identified in the Sloan Digital Sky Survey.  See also EurekAlert.  The original paper was published in Nature.¹  “Our analysis shows that the atmospheric parameters found for these stars do not fit satisfactorily in any of the currently known theories of post-asymptotic giant branch evolution,” the abstract states.

1.  P. Dufour, J. Liebert, G. Fontaine and N. Behara, “White dwarf stars with carbon atmospheres,” Nature 450, 522-524 (22 November 2007) | doi:10.1038/nature06318.

This portion of the news is brought to you by the makers of Humble Pie, reminding you that moderation in science is a good thing.
    “Twinkle twinkle little star, I don’t wonder what you are; for by spectroscopic ken, I know that you are hydrogen.”  So astronomers used to say.  Always be wary when a scientist says, “I know.”  What rhymes with carbon?
    If they had only found seven of these unexpected stars, we could have spun some fairy tales about Snow White Theories and the Seven Dwarfs getting lost in the Data Mine.  We’ll show moderation, though, and not discuss which astronomers were sleepy, dopey or grumpy.