Ethan Siegel in Starts With A Bang:
Every once in a while, a star in our own galaxy can do something to surprise us. Over in the constellation of the Unicorn lived a quiet, run-of-the-mill star named V838 Monocerotis. But in early 2002, it brightened incredibly rapidly, and the before-and-after pictures were rather astonishing.
What was initially thought to be a nova turned out to be much, much more fascinating by time the Hubble Space telescope got around to looking at it in May of 2002.
Warning: what you're about to see may shock you!