“The new object, which appeared in May 2009, has left us scratching our heads - we’ve never seen anything quite like this before,” said Dr Muxlow. “The object turned on very rapidly within a few days and shows no sign of decaying in brightness over the first few months of its existence. The new young supernova explosions that we were expecting to see in M82 brighten at radio wavelengths over several weeks and then decay over several months, so that explanation seems unlikely.”
The object is not quite in the middle of M82, where astronomers would expect to find the kind of supermassive central black hole that most other galaxies, including the Milky Way, have. Which leaves the possibility that it could be a smaller-scale "microquasar".
We won't know for sure what it is for years to come. But if we start getting reruns of an alien version of I Love Lucy I will be endlessly amused.