FWD: [UASR] Astronomers puzzled by brightening of star
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Astronomers puzzled by brightening of star
CHICAGO, June 2 (Reuters) - The brightest known star in the universe is
radiating twice as much light as it did 20 years ago, puzzling astronomers
who said on Wednesday they could not explain the sudden change.
The star, known as Eta, is about 7,500 light-years from Earth, and is visible
to the naked eye in the southern hemisphere. The star sits between two huge
lobes of gas and dust that were formed by a tremendous explosion observed
about 150 years ago.
Astrophysicists at a meeting of the American Astronomical Society in Chicago
said they had expected Eta's spectrum to change in 1998, but did not foresee
a major jump in brightness. The central star has more than doubled in
brightness since 1977, after dimming somewhat from 1992 to 1997.
``Eta's brightness routinely wiggles plus or minus 10 percent,'' said Kris
Davidson, an astrophysicist at the University of Minnesota. ``But we've
gotten four spectra from (the Hubble Space Telescope) in the last two years,
and its brightness is rising at an incredible rate.''
Eta's brightening was all the more puzzling because it was happening
uniformly at all wave lengths. Scientists had expected that as the object
cooled off, its spectrum would dim at the more energetic ultraviolet
wavelengths. Instead, its across-the-board brightening was similar to some
kind of cosmic shroud was being lifted, said Roberta Humphreys, another
astrophysicist at the University of Minnesota.
``The clearing of dust in our line of sight could do that kind of thing, but
that's a lot to ask of dust,'' Humphreys said. ``Dust is coming out from Eta
in all directions. Therefore, it's unlikely that a cloud of dust just moved
across our line of sight and is now clearing.''
Astrophysicists consider Eta one of the most enigmatic celestial objects. The
star radiates a stream of energetic particles, called a stellar wind, that is
100 to 1,000 times stronger than the winds generated by most massive stars.
Every millennium, Eta loses enough mass to equal that of our sun, Davidson
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