Caroline Moore, a 14 year old student in New York, discovered the supernova SN 2008ha in a galaxy 70 million light-years away last year. This makes her the youngest person known to have discovered a supernova, which is interesting in itself and reminds us that scientific discovery is not just limited to professional scientists with extensive training and access to expensive instruments. What's even more interesting is that she discovered the weakest supernova ever observed. In fact, I'm not quite certain if it even was a supernova, being far more weaker than other supernova but still far more powerful than a nova.
SN 2008ha was a stellar explosion of a type never seen before. While the consensus seems to be that it was indeed a supernova of some sort, there is disagreement on exactly what sort of supernova it may have been. The lack of hydrogen in the observed spectra indicates that it may have been similar to a Type Ia supernova, which explodes from a runaway fusion reaction when enough matter accretes on a white dwarf. The only problem with this is that the way Type Ia supernova occur suggests that they should all have pretty much the same brightness, and SN 2008ha is far more weaker than the typical Type Ia supernova. An alternative explanation is that it may have been more like a Type II supernova where a massive star implodes, except in this case the massive star in question may have lost much of its hydrogen and had only a "little" of the energy escape the implosion.
And then there's my own favorite theory: it's an alien power station gone kaboom.