SEATTLE, WASHINGTON—Last year NASA scientists trained orbiting and ground-based observatories on one of the most bizarre and violent systems in our galaxy: Eta Carinae, a binary system made up of two enormous unstable stars that orbit each other every 5.5 years. “It’s an erratic stellar monster,” astronomer Michael Corcoran of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, told a press conference at the American Astronomical Society here today. The huge stars, one about 100 times as massive as the sun and the other about 30 times, are blowing off material in stellar winds at a furious rate—roughly the mass of Jupiter every year. “They’re blowing themselves apart,” Corcoran says. The orbit takes the stars far apart for most of the time, but once per orbit they approach very close and the competing solar winds—traveling at 420 kilometers per second from the large star and up to 3000 km/s from the smaller—create a bow shock, heating the gas to tens of millions of degrees. At that temperature, the gas emits x-rays, hence NASA’s Swift satellite was focused on the latest close approach last year. NASA researchers have used last year’s observations to refine computer simulations of the system and to produce 3D printed models (pictured, and available to download), which have helped them discover fingerlike protrusions from the bow shock. “We think these arise from physical instabilities in the heated gas,” Goddard’s Thomas Madura says. For reasons that scientists don’t understand, the system produced a huge eruption of material—equivalent to 30 solar masses—in the 1840s. “We don’t know which of the stars had the great eruption. It’s still a bit of a mystery,” Madura says. This instability makes Eta Carinae a prime candidate to explode as a supernova or even hypernova in our vicinity. If that happens, says Goddard’s Theodore Gull, it will be visible in daytime, “a comparable brightness to the moon.”*Correction, 7 January, 8:55 p.m.: This item originally stated material equivalent to “30 million solar masses” erupted from Eta Carinae in the 1840s. It should be “30 solar masses”. We have updated the item to correct this.