Last century, a massive binary system went supernova, ejecting at least 10 times the mass of our Sun into space. NASA scientists have now created the first hi-res model of the expanding cloud produced by this iconic outburst.
During the eruption, which occurred between 1838 and 1845 (at least from our perspective in the Hubble Bubble; the object is located about 7,500 light-years away), a huge gaseous shell was shot into space. The resulting explosion, what we call Eta Carinae, went on to become the second-brightest star in our sky. The blast area now forms a twin-lobed and dust-filled cloud known as the Homunculus Nebula. The spectacular stellar object is currently about one light-year long as it continues to expand at more than 1.3 mph (2.1 million km/h).
The new model was compiled using new observations made by the European Southern Observatory's Very Large Telescope and its X-Shooter spectrograph over two nights in March 2012. The team imaged near-infrared, visible and ultraviolet wavelengths along 92 separate swaths across the nebula; it's considered the most complete spectral map to date. A software program called "Shape" was used to create the 3D modeling.
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The new shape model confirms several features identified by previous studies, including pronounced holes located at the ends of each lobe and the absence of any extended molecular hydrogen emission from a dust skirt apparent in visible light near the center of the nebula. New features include curious arm-like protrusions emanating from each lobe near the dust skirt; vast, deep trenches curving along each lobe; and irregular divots on the side facing away from Earth.
"One of the questions we set out to answer with this study is whether the Homunculus contains any imprint of the star's binary nature, since previous efforts to explain its shape have assumed that both lobes were more or less identical and symmetric around their long axis," explained team member Jose Groh, an astronomer at Geneva University in Switzerland. "The new features strongly suggest that interactions between Eta Carinae's stars helped mold the Homunculus."
Every 5.5 years, when their orbits carry them to their closest approach, called periastron, the immense and brilliant stars of Eta Carinae are only as far apart as the average distance between Mars and the sun. Both stars possess powerful gaseous outflows called stellar winds, which constantly interact but do so most dramatically during periastron, when the faster wind from the smaller star carves a tunnel through the denser wind of its companion. The opening angle of this cavity closely matches the length of the trenches (130 degrees) and the angle between the arm-like protrusions (110 degrees), indicating that the Homunculus likely continues to carry an impression from a periastron interaction around the time of the Great Eruption.
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Images: Image Credit: NASA's Goddard Space Flight Center/Ed Campion