Mega Star Viewed In Unprecedented Detail

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A star millions of times as bright as the sun has been imaged using a combination of space and Earth-based telescopes to provide extraordinary detail. The observations could help us predict when the star will go through an explosion that is likely to offer us a spectacular show.

Within the Eta Carinae stellar system is a truly phenomenal star, with an estimated mass so great it has forced us to reconsider how heavy stars can be without blowing themselves apart. More massive stars have since been found, and it is thought they once grew bigger still, but nothing so large is anything like it so close.

In 1843, Eta Carinae had an extraordinary outburst, making it temporarily the second brightest star in the sky. Its fading is thought to result from a cloaking cloud of dust, rather than any diminution of emitted light.

We now know Eta Carinae is two stars orbiting each other with a period of 5.5 years. The larger star was once 150 times the mass of our sun, but is now down to around 120 solar masses, while the smaller is a still huge 30 solar masses.

The enveloping gas and dust thrown off by Eta Carinae’s A’s activity is so thick that for a long time there was debate about whether a second star even existed. Now NASA has mapped their interaction and the effect of their stellar winds on the surrounding gasses with extraordinary accuracy, including stitching together 41 Hubble images covering gas clouds a tenth of a light-year wide.

The stars’ orbits are very elongated, and when these stars are closest together (periastron) interesting things happen, including X-ray flares followed by a sudden quiet. One periastron occurred in 2014, and astronomers now think they are coming to understand what they witnessed. To solidify their thinking, the NASA scientists used a 3-D printer to create models of the system with the stars at different orbital stages.

They believe the key to what was seen during the last three periastrons is the way the two stars’ stellar winds interacted with each other and the gas around them. In keeping with their size, both stars have hugely powerful stellar winds, but with differing compositions – thick and slow for Eta Carinae A, six times faster and a hundredfold less dense for its companion.



“We are coming to understand the present state and complex environment of this remarkable object, but we have a long way to go to explain Eta Carinae’s past eruptions or to predict its future behavior,” said Dr. Ted Gull of the Goddard Space Flight Center. The Goddard team have created a model that predicts how each periastron will differ, but face a frustrating wait until 2020 before they can test it out.

Credit: NASA’s Goddard Space Flight Center/T. Madura Simulation with Eta Carinae A and B as black dots and lighter colors showing denser stellar winds.

Stars larger than eight times the mass of the sun end their life in supernovae explosions. We know much less about stars 15 times larger, but suspect they put on quite a show and Eta Carinae A may be ready to blow.

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