[4] M82 X-2 is an ultraluminous X-ray source (ULX), shining about 100 times brighter than theory suggests something of its mass should be able to.

Possible explanations for violations of the Eddington limit include geometrical effects arising from the funneling of in-falling material along magnetic field lines.

While M82 X-2 was previously known as an X-ray source, it was not until an observation campaign to study the newly discovered supernova SN 2014J in January 2014 that X-2's true nature was uncovered.

[5][6] Scientists looking at data from the NuSTAR spacecraft noticed a pulsing in the X-ray spectrum coming from near the supernova in Messier 82.

[2][7] Data from the Chandra and Swift spacecraft was used to verify the NuSTAR findings and provide the necessary spatial resolution to determine the exact source.