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A new close-up view of the violent surroundings of the brightest known star in the Milky Way Galaxy confirms the unstable beast's years are numbered. The study also yields new insight into the huge, eruptive star.
Eta Carinae is 100 times more massive than the Sun and 5 million times as luminous.
The monster, as astronomers have described it, had a dramatic outburst in 1841, shining for a time as the second brightest star in Earth's night sky despite being about 7,500 light-years away, or roughly 1,000 times farther away than Sirius, the
brightest star in the sky.Eta Car, as astronomers call it, could erupt again at any time and will eventually explode in a life-ending supernova event that might be visible during the day from Earth, if anyone is still around to watch.
The 1841 eruption created two massive, mushroom-shaped lobes of material that astronomers now study with high-powered telescopes. Thing is, the stuff in the lobes, along with a constant stream of charged particles still emanating from the scene, obscure the star itself.
The new observations got closer than ever.
Astronomers have still not seen the star, but they used the Very Large Telescope at the European Southern Observatory (ESO) in Chile to examine its immediate surroundings. A study of the data, announced last week, shows Eta Carinae is on the verge of instability, rotating at about 90 percent of the maximum speed possible prior to a theoretical breakup.
The observations, in infrared light, detail a "wind" of charged particles plowing out from the star. Our own Sun produces a constant high-speed outflow known as the solar wind. But it is a mild breeze compared to the stellar wind of Eta Car, which blows off the equivalent of 500 Earth masses every year, said study leader Roy van Boekel of the ESO and the University of Amsterdam.
"If Eta Car goes on like this, all of its estimated 100 solar masses would be blown away in about 60,000 years," van Boekel told SPACE.com. The star's life will be shorter if there are more large outbursts like the one in 1841, when perhaps 10 solar masses were ejected, he said.
It is more likely, however, that Eta Carinae will go supernova long before it simply withers away. That dramatic event could occur within 10,000 or perhaps 20,000 years.
Meanwhile, Eta Carinae
shrouds itself in mystery. "The stellar wind that surrounds it is so dense that basically all photons leaving from the star are absorbed in the wind," van Boekel said. The new observations allowed van Boekel and his colleagues to map the shape of the constant outflows, which in turn provided clues to the orientation and dynamics of the unseen star.
They found that Eta Carinae's stellar wind is elongated in the polar direction. Here's why:
"The stellar wind occurs because atoms at the surface of the star are bombarded with so many photons, that they can be blown away," he said. "The star itself is flattened by the centrifugal force arising from its rotation."
Its diameter at the equator is larger than when measured pole-to-pole.
"This causes the temperature of the star to be higher at the poles, and therefore every square foot of stellar surface at the poles emits more photons than the same area at the equator," van Boekel continued. "As more photons can blow away more atoms, the stellar wind is stronger in the polar direction."
The fresh examination fits neatly with previous examinations of the mushroom shaped lobes, which astronomers call the Homunculus Nebula. The current polar outflows appear to be lined up with the much larger homunculus.
"The assumption is that the major axis of the homunculus coincides with the rotation axis of the star," van Boekel said.
Eta Carinae's nebula is visible from the Southern Hemisphere.
Eta Carinae's Nebula, Up Close
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