Credit: Movie: Christopher M. P. Russell (Pontificia Universidad Católica de Chile); Thumbnail: T. Madura & NASA/GSFC
Eta Carinae: A Star-Winds Story
The Eta Carinae star system is the most massive and brightest object within about 10,000 lightyears. Based on periodic variations seen in its infrared and X-ray emission, we know that Eta Carinae is a binary system in which one very massive star, containing about 30 times the Sun's mass, orbits one of the most massive stars in our Galaxy. This star, Eta Carinae A, erupted most noticeably in the mid-nineteenth century, an event nearly as powerful as a supernova, and the remnants of this explosion can still be seen as a bipolar, dusty, massive nebula called the Homunculus, which surrounds the star system and hides it from direct view. Eta Carinae A contains close to 100 times the Sun's mass, and because of this, the star generates so much radiation that it's literally blowing itself apart. Material is flying off Eta Carinae A in the form of a thick, slow stellar wind. The wind is so dense that the star loses about the Sun's mass of material in only 1000 years. The companion star is also extremely luminous and generates a weaker wind which rams against the wind of Eta Carinae A, forming a conical, colliding wind shock of very hot gas around the companion. As the stars orbit each other, the X-ray emission from this bow shock is seen to vary. The changes in the observed X-ray emission help us understand the orbit of the two stars and derive important physical properties about the stars themselves (indeed the companion star best makes itself known by way of this X-ray emission). The movie in the upper left shows a portion of a 3-D simulation of the variation in the shape and location of the colliding wind bow shock as the two stars orbit around each other. Large changes are apparent since the orbit is extremely eccentric, so that the separation of the stars varies by a factor of 10 or so. The other panels show details of the shape and velocity of the X-ray emitting gas as the stars revolve. The Eta Carinae system has an orbital period of 5.5 years, and this month the stars are passing the point of closest approach, when the X-ray emission disappears as the companion passes behind the massive primary.
Published: February 17, 2020
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