Eta Carinae's star turn puzzles astronomers.

Tempestuous as a diva and just as unpredictable, the massive star Eta Carinae is stunning astronomers with its brightest performance in over a century. Observations taken with the Hubble Space Telescope between December 1997 and this February reveal that the star had more than doubled its brightness and that the light emitted by the billowing gas and dust immediately surrounding it had tripled its intensity.

"This is the largest and most rapid brightening of Eta Carinae in the past 50 years, and the object is now brighter than at any time in the past 130 years," elated researchers reported in an April 19 circular of the International Astronomical Union. This week, the team, which includes Kris Davidson of the University of Minnesota in Minneapolis and Theodore R. Gull of NASA's Goddard Space Flight Center in Greenbelt, Md., described their latest analyses to SCIENCE NEWS.

The recent activity might be a prelude for the kind of light show that made Eta Carinae famous 150 years ago. Visible to the naked eye, it resides 7,500 light-years from Earth in the constellation Carina. In the 1840s, Eta Carinae hurled into space two ballooning gas clouds, ejecting as much mass as would be found in three suns and temporarily becoming the second brightest star in the sky. It underwent a smaller burst 50 years later, and in late 1997 showed an unprecedented upswing in the intensity of X rays it emits (SN: 2/7/98, p. 88). But after making a spectacle of itself, Eta Carinae seemed to be settling down.

"When there is an eruption, it stabilizes the star for a long time afterward," Davidson says. He would have expected another outburst in 2200 or 2300. "It looks like it's throwing all the hand-waving theories out the window," he notes.

Gull suspects that in addition to an increase in the star's luminosity, some of the recent brightening may be due to the clearing of its dust veil, which would allow more starlight to emerge. Increased ionizing radiation from the star may cause some of the surrounding dust to evaporate, he says. Davidson cautions, however, that it's unlikely dust could vanish so rapidly.

Several astronomers, including Elisha Polomski of the University of Florida in Gainesville, have confirmed the Hubble observations. Using a 4-meter telescope at the Cerro Tololo Inter-American Observatory in La Serena, Chile, Polomski and her colleagues have found that since 1997, the amount of mid-infrared radiation emitted by dust surrounding the star has doubled.

"If the only evidence were in the Hubble Space Telescope data, I'd be really nervous about its reality," says Davidson. But at this point, "the only way all this stuff could be a mistake is if everyone concerned.., has simultaneously erred in the same direction."

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