The culprit is what's known as a neutron star, the tiny but very dense corpse of a massive star that died in a supernova blast. Sitting 16,000 light-years away, this particular neutron star is normally among the faintest objects in the x-ray sky.

But during recent observations with the European Space Agency's XMM-Newton space telescope, the star unexpectedly surged to 10,000 times its original brightness.