A star in Scorpius likes to blow off steam. It stages big outbursts every decade or so. And the next one could happen any day now.
U Scorpii is a system of two stars that are only a few million miles apart. One of the stars is at the end of its “normal” lifetime, so it’s starting to puff up. The other has already ended its life, so only its hot, dead core remains — a white dwarf.
The white dwarf “steals” gas from its companion. The gas forms a disk around the white dwarf. Some of the gas funnels onto the star’s surface. As it builds up, it gets hotter. Eventually, it gets hot enough to trigger a nuclear explosion. That blasts the built-up gas out into space.
U Scorpii erupts about every 10 years. The most recent outburst came in January of 2010. In a few hours, the system grew about 10,000 times brighter than average. It then faded quickly. Within a few days, though, the white dwarf was already pulling in more gas. But observations over the following years showed that it took about 18 months to fully reestablish the disk of gas around the star.
Astronomers expect to see the next eruption this year. In fact, it’s possible that it’s erupted since we recorded this program. Whenever it happens, astronomers will keep a close eye on U Scorpii — watching it once again blow off some steam.
The system stands above Antares, the scorpion’s bright orange heart, which is in the south as night falls. More about Scorpius tomorrow.