Ad Astra Observatory

Just read the press release — they had calculated, based on supernova frequency in other galaxies, that about 3 SN per century should pop off in any given galaxy (like the Milky Way, for instance). But no known
supernova had been seen since Casseiopeia A popped in 1680. That means there should be 10 SN remnants that should be lurking out there that we hadn’t seen yet, and they found the first one.

It apparently popped ~140 years ago, but is behind a dense chunk of galactic dust from us, so they had to detect it in X-Rays.