Free Astronomy Magazine September-October 2018

51 SEPTEMBER-OCTOBER 2018 SPACE CHRONICLES T his six-panel graphic illustrates a possible scenario for the powerful blast seen 170 years ago from the star system Eta Carinae. 1 - Eta Carinae initially was a triple-star system. Two hefty stars (A and B) in the system are orbiting closely and a third companion C is orbiting much farther away. 2 - When the most massive of the close binary stars (A) nears the end of its life, it begins to expand and dumps most of its material onto its slightly smaller sibling (B). 3 - The sibling (B) bulks up to about 100 solar masses and becomes extremely bright. The donor star (A) has been stripped of its hydrogen layers, exposing its hot helium core. The mass transfer alters the gravitational balance of the system, and the helium-core star moves farther away from its monster sibling. 4 - The helium-core star then interacts gravitationally with the outermost star (C), pulling it into the fray. The two stars trade places, and the outermost star gets kicked inward. 5 - Star C, moving inward, interacts with the extremely massive sibling, creating a disk of material around the giant star. 6 - Eventually, star C merges with the hefty star, producing an explosive event that forms bipolar lobes of material ejected from the monster sibling. Meanwhile, the surviving companion, A, settles into an elongated orbit around the merged pair. Every 5.5 years it passes through the giant star’s outer gaseous envelope, producing shock waves that are detected in X-rays. [NASA, ESA, and A. Feild (STScI)] a violent explosion when Eta Carinae devoured one of its two compan- ions, rocketing more than 10 times the mass of our Sun into space. The ejected mass created gigantic bipo- lar lobes resembling the dumbbell shape seen in present-day images. The results are reported in a pair of papers by a team led by Nathan Smith of the University of Arizona in Tucson, Arizona, and Armin Rest of the Space Telescope Science Institute in Baltimore, Maryland. The light echoes were detected in visible-light images obtained since 2003 with moderate-sized tele- scopes at the Cerro Tololo Inter- American Observatory in Chile. Using larger Magellan telescopes at the Carnegie Institution for Sci- ence’s Las Campanas Observatory and the Gemini South Observatory, both also located in Chile, the team then used spectroscopy to dissect the light, allowing them to measure the ejecta’s expansion speeds. They clocked material zipping along at more than 20 million miles per hour (fast enough to travel from Earth to Pluto in a few days). The observations offer new clues to the mystery surrounding the titanic convulsion that, at the time, made Eta Carinae the second-brightest nighttime star seen in the sky from Earth between 1837 and 1858. The data hint at how it may have come to be the most luminous and mas- sive star in the Milky Way galaxy.