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Eta Carinae II

June 17, 2014

Astronomers in the southern hemisphere will be paying close attention to an impressive star system this summer. The system’s two stars will be passing closest to each other, at perhaps no more than the distance from Earth to the Sun. That should produce dramatic changes in the system’s light — and perhaps in its larger star.

Eta Carinae is one of the most massive binaries in the galaxy — a pair of supergiants that together shine about five million times brighter than the Sun.

These massive stars produce strong “winds” of hot gas. When the winds ram together, they get even hotter, so they emit lots of X-rays.

The stars follow a highly elongated orbit around each other. When they get closest, as they will next month, the wind from the larger star may overpower that of the smaller star. The battleground between the two winds may then collapse onto the smaller star, so the X-rays will go away.

Some astronomers think the close encounter may make the bigger star spin faster. In fact, it may spin so fast that it becomes unstable, eventually staging a powerful eruption.

One such eruption was seen in the 1840s. And there’s evidence that the star may be building up to another. Perhaps repeated close encounters — one every five-and-a-half years — have once again made the bigger star unstable.

Observations of this year’s close approach may help astronomers better understand whether that model is correct — and Eta Carinae is headed for another big blast.

More tomorrow.

Script by Damond Benningfield, Copyright 2014

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