Study sheds light on double-star explosions
Thursday, 08 Mar 2007 08:25
Z Cam includes a collapsed dead star
Science In Focus
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New information gathered by Nasa has given weight to a 20-year-old theory that binary star systems are capable of experiencing both small and giant explosions.
The US space agency's galaxy evolution explorer (Galex) has collected new data showing that the double-star systems cycle between differing blast types, rather than experiencing just one.
Researchers, including the Carnegie Observatories' Mark Seibert, analysed the information on cataclysmic binary system Z Camelopardalis (Z Cam), which includes a collapsed dead star known as a white dwarf.
Z Cam, which is 530 light years from earth, has been revealed as a "stellar vampire" by ultraviolet images taken by Galex.
The images showed a never seen before arc and linear feature surrounding the double-star system; evidence that the dwarf nova had experienced traditional nova explosions in the past thousand years.
"You could actually see it immediately, but we had to convince ourselves that we were really seeing a nova remnant," writes Professor Seibert in the Nature journal.
"If true, it would represent the largest nova remnant yet known. But it was especially shocking to find it associated with such a diminutive dwarf nova system. Everyone was sceptical and it took a considerable amount of time and effort to be certain."
And lead study author Mike Shara of the American Museum of Natural History in New York commented that the new data was the "strongest evidence" yet for the cyclical nature of binary stars.
"It's gratifying to see such strong evidence for this theory finally emerge after all this time," he added.
Dwarf nova are unique as rather than occurring through the accretion of hydrogen they come about via inherent instability that causes binary stars to collapse into the white dwarf.