Thursday, February 16, 2012

Eta Carinae: Echoes of the Ancient 'Great Eruption' Reach Astronomers

When the binary star system Eta Carinae experienced a spectacular outburst in 1837, dubbed the "Great Eruption," there were no cameras or other sophisticated scientific instruments around to record the event for posterity.

But now, 170 years later, remnants of light from the Great Eruption are finally reaching Earth, providing new insight into how massive stars behave when they are on the brink of exploding.

Astrophysicists at the University of California, Santa Barbara and the Las Cumbres Observatory Global Telescope Network, announced the detection of this "light echo" in a Feb. 16 letter to the journal Nature.

UCSB Postdoc Federica Bianco, who compared the light echo to eyewitness reports from the 1800s, phrased the phenomenon best: "You are at the stadium, watching the game, and your team scores. But you do not have modern instruments, detectors and spectrographs to study it," she said in a press release.

"Now we are getting a replay -- an up-close detailed view of our cosmic eruption," she continued. "And just like with the replay, we get to see the outburst from a different point of view, as the light that we see now was originally traveling in a different direction than the light seen in the 1840s."

Eta Carinae is a rare, massive binary star, and the dominant partner in this cosmic coupling belongs to the class of luminous blue variable stars. When it erupted 170 years ago, it became one of the brightest stars in the sky for a time. So why are we suddenly seeing light from that event again?

The astrophysicists explain that originally, the light traveled away from Earth, and then bounced off dust clouds, which rerouted it to Earth -- just like an echo. The longer path means we are only now seeing that echo.

There might not be photographs, but there are a few historical eyewitness accounts on record to help astrophysicists determine that what they are seeing really is a "light echo" from Eta Carinae's 19th century outburst.

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