Credit: NASA/CXC/GSFC/K.Hamaguchi, et al.
Down Low
Eta Carinae, that doomed star, is acting up on cue. This extremely massive star is notorious for episodes in the 1800s when it, for some still unknown reason, decided to eject about 1/5 of its mass into circumstellar space. We can still see the results of this outburst as the well-known, beautiful, bizarre Homunculus, a massive, dusty, bipolar nebula surrounding the star. Astronomers recently have been able to determine the 3-D structure of this nebula, providing a detailed look at the ejected mass, which you can print and hold in your hand. Eta Car is a binary system, orbited by another massive star whose presence is only indirectly detected by the collisions of the powerful stellar winds the two stars possess. This collision carves an enormous cavity in eta Car's stellar wind, and also generates 50 million degree gas that produces X-ray emission. The companion moves in an extremely elliptical orbit, so that the separations between the two stars vary enormously, and the observed X-ray emission varies enormously as well. Every five and one half years, the companion moves behind eta Car and comes so close that it nearly skims its surface. This time of closest approach, or periastron, has just occurred, producing a characteristic faint state in the observed X-ray emission, which astronomers are studying with all the X-ray telescopes at their disposal. The image above shows X-ray emission around the eta Car system as seen by the Chandra X-ray Observatory during the previous two X-ray minima. The orange extended emission is produced by hot gas associated with shocked outer gas beyond the Homunculus. Hot X-ray emitting gas associated with the eta Car binary system itself is seen as the white dot at the center of the image. At the time of this image there's little X-ray emission from the wind-wind collision, so you can see faint blue emission from X-rays reflected by the cold gas in the Homunculus around eta Car.
Published: September 8, 2014
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