Aquila, the eagle, spreads its wings across the evening sky as we head into summer. Right now, it’s low in the east a couple of hours after sunset. Its brightest star, Altair, is at the bottom right point of the wide-spread Summer Triangle. Altair represents the eagle’s breast, with the wings above and below. A pair of stars at one of the wingtips faces a spectacular future. The two stars will ram together, then explode as a supernova — in about 700 million years. The system is known as Henize 2-248. It consists of two white dwarfs — the dead cores of once-normal stars like the Sun. They’re only a few hundred thousand miles apart — so close that they orbit each other once every four hours. As they orbit, though, they radiate gravitational waves — a process that causes them to spiral closer and closer. Each of the stars is a bit less massive than the Sun. So when they merge, the combined star will be almost twice as massive as the Sun. And for a white dwarf, that’s a bad thing. With tha
