When we look at the night sky, it’s like being stuck watching just one TV channel or visiting just one web page. There’s a lot more to see, but our eyes can’t tune to the other channels.
One of those missing channels is the UV channel. Ultraviolet energy is produced by some of the hottest and brightest objects in the universe. That includes massive young stars, which are tens of thousands of degrees hotter than the Sun. They can emit dozens of times more ultraviolet light than visible light; more about that tomorrow.
Other UV targets include the remnants of exploded stars, and the disks of superhot gas around black holes. Studying these objects in the ultraviolet reveals details about their temperature, chemical composition, and other characteristics that we can’t see in other wavelengths.
Fortunately, we can build instruments that allow us to see the ultraviolet glow of these objects. But the ozone in Earth’s upper atmosphere blocks most ultraviolet wavelengths, so they never reach the ground. To see the ultraviolet, then, the instruments have to be launched into space.
Over the decades, more than a dozen UV telescopes have been launched. They’ve detected and studied thousands of objects. Their observations have helped astronomers find and map the birthplaces of new stars, peel back the layers of exploding stars, and study how hot gas funnels into black holes — switching on an exciting new channel in our study of the universe.