NASA created a stunning picture of Eta Carinae, a gigantic stellar system that surprised scientists by erupting twice in the 19th century and contains a number of other puzzling features.
Researchers used NASA satellites, ground-based telescopes and theoretical modeling to produce the most comprehensive picture of the mysterious system to date. The findings include images that show decades-old shells of ionized gas shooting away from Eta Carinae's largest star at a million miles an hour.
"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 Goddard astrophysicist Ted Gull, who coordinates a research group that has monitored the star for more than a decade.
Eta Carinae is located 7,500 light-years away in the southern constellation of Carina and is made up of two massive stars that orbit unusually close to each other every five and a half years. Both give off gaseous flows called stellar winds, which have made it difficult for researchers to measure these stars' properties
Astronomers have observed dramatic changes in the system in the months before and after the star's closest approach to each other. These changes included X-ray flares followed by a recovery in X-ray emission; the disappearance of objects detected near stars at certain wavelengths; and a strange display of light and shadow detected as the small stars move around the primary stellar object.
"We used past observations to construct a computer simulation, which helped us predict what we would see during the next cycle, and then we feed new observations back into the model to further refine it," said Thomas Madura, a NASA postdoctoral program fellow at Goddard and a theorist on the Eta Carinae team.
The model suggests the interaction of two stellar winds accounts for many of the previously unexplained changes seen in the system. When the companion star swings around the primary, its faster wind (which is also less dense) carves out a spiral cavity in the denser wind of the primary star. The researchers also observed X-rays from the system carry information directly from the wind collision zone, where the shockwaves heat the gas to millions of degrees.
"Changes in the X-rays are a direct probe of the collision zone and reflect changes in how these stars lose mass," said Michael Corcoran, an astrophysicist with the Universities Space Research Association headquartered in Columbia, Md.
The new image shows the observed doubly ironed emissions are born by complex gaseous structure nearly one-tenth of a light-year across, which Gull compared to Maryland blue crabs. In which the shells of gas representing the crab's "claws" were observed moving away from the stars at speeds of up to a million miles per hour.
"These gas shells persist over thousands of times the distance between Earth and the sun," Gull explained. "Backtracking them, we find the shells began moving away from the primary star about 11 years or three periastron passages ago, providing us with an additional way to glimpse what occurred in the recent past."
When the stars approach each other the companion becomes immersed in the primary's dense winds, preventing its UV light from reaching the gas shell. When this energy is taken away the doubly ionized iron ceases to emit light and the "crab" structure disappears at this wavelength. Once the companion moves away from the densest wind its light can once again escape and re-energizes the iron atoms of the shell, allowing the crab to return.
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