Free Astronomy Magazine September-October 2018

50 SEPTEMBER-OCTOBER 2018 SPACE CHRONICLES Astronomers uncover new clues to the star that wouldn’t die by NASA/ESA W hat happens when a star behaves like it exploded, but it’s still there? About 170 years ago, astronomers witnessed a major outburst by Eta Carinae, one of the brightest known stars in the Milky Way galaxy. The blast unleashed almost as much en- ergy as a standard supernova explo- sion. Yet Eta Carinae survived. An explanation for the eruption has eluded astrophysicists. They can’t take a time machine back to the mid-1800s to observe the outburst with modern technology. However, astronomers can use na- ture’s own “time machine,” courtesy of the fact that light travels at a fi- nite speed through space. Rather than heading straight toward Earth, some of the light from the outburst rebounded or “echoed” off of inter- stellar dust, and is just now arriving at Earth. This effect is called a light echo. The light is behaving like a postcard that got lost in the mail and is only arriving 170 years later. By performing modern astronomical forensics of the delayed light with ground-based telescopes, astrono- mers uncovered a surprise. The new measurements of the 1840s eruption reveal material expanding with record-breaking speeds up to T his animation shows how the massive star Eta Carinae survived a major erup- tion in the 1840s. In this scenario, Eta Carinae initially began as a triple-star sys- tem. Two hefty stars in the system are orbiting closely and a third companion is orbiting much farther away. When the most massive of the close binary stars nears the end of its life, it begins to expand and dumps most of its material onto its sib- ling. The sibling bulks up and becomes extremely bright. The donor star, having lost most of its mass, moves farther away from its monster sibling and interacts with the outermost star. The two stars trade places, with the outermost star get- ting kicked inward. The inward-moving star falls into the monster sibling, and the two stars merge. The merger produces an explosive event that forms bipolar lobes of material ejected from the giant star. The surviving companion star settles into an elongated orbit around the merged pair, passing through the monster star’s outer gaseous envelope every 5.5 years. [NASA, ESA, and G. Bacon (STScI)] 20 times faster than astronomers ex- pected. The observed velocities are more like the fastest material ejected by the blast wave in a supernova ex- plosion, rather than the relatively slow and gentle winds expected from massive stars before they die. Based on this data, researchers sug- gest that the eruption may have been triggered by a prolonged stel- lar brawl among three rowdy sibling stars, which destroyed one star and left the other two in a binary system. This tussle may have culminated with