If you include "look", you can gamma ray bursts[0] to the list. As summarized in the wikipedia article, gamma ray bursts were originally discovered by the Vela satellites, which were looking for nuclear weapons tests in space. They discovered multiple bursts of gamma rays, coming from outside the solar system. Some of these bursts (the long ones, longer than about 2 seconds)) are now know to be associated with supernovae, while the origin of the short bursts is still uncertain.<p>[0] <a href="https://en.wikipedia.org/wiki/Gamma-ray_burst" rel="nofollow">https://en.wikipedia.org/wiki/Gamma-ray_burst</a>