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Now you see it, now you don't.

Now you see it, now you don't

The sudden disappearance of a star often provides a clear sign that an unseen, orbiting companion has moved in front of it, blocking the star's light. Eventually, as the obscuring companion moves aside, the star reappears. In the case of an unusual blue star (designated PG 1500+131) in the constellation Ophiuchus, the reappearance happens after only 12 minutes. Observed last summer by Reinhold Hafner of the European Southern Observatory at La Silla in Chile, this vanishing act represents the most complete and arguably the fastest stellar eclipse yet seen.

The double-star system apparently consists of one star that has already evolved into a small, bright, compact object (a white dwarf) and another, faint star (a red dwarf) still in the main phase of its life, converting hydrogen fuel into helium. When the fainter star passes in front of its brighter partner, only light from the fainter star is visible. Because the darkening is so complete, the red dwarf must be less than one-hundredth as bright as the white dwarf. Moreover, the short duration of the eclipse indicates the faint star is also very small. The two stars orbit roughly 700,000 kilometers apart, meaning the entire system would fit within the space filled by our sun.

The discovery of this binary star system provides important information about a rarely observed phase in the evolution of binary stars. The stars seem in a state that immediately precedes the unstable "cataclysmic" phase, in which a stream of gas begins to flow from the larger to the smaller star, causing the smaller star to brighten abruptly. Futher observations of the system are planned for later this year.
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Title Annotation:stellar eclipse in constellation Ophiuchus
Publication:Science News
Date:Jan 7, 1989
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