It's named "52-Hertz" because that is the frequency at which it sings. Science doesn't know which species of whale our 52-Hertz belongs to.
The dear 52-Hertz is one of a kind. It could be the "last of a previously unknown species of baleen whale"; it could be "malformed, or maybe a rare hybrid — perhaps a blue whale and fin whale cross."
There is no clear photo evidence of 52-Hertz, which makes identifying it even more difficult.
A team of marine researchers tracked its movements for about a decade.
The Woods Hole Oceanographic Institution on Cape Cod recorded and tracked frequencies of whale sounds coming from the North Pacific using hydrophones (which were originally "used by the Navy to monitor enemy submarines"). The travel pattern of the 52-Hertz whale somewhat matches that of the grey whale.
According to Lilly Sullivan, author of this public radio story about 52-Hertz, one of the original researchers has begun his quest of finding this whale. Joseph George explains that he has never seen 52-Hertz, and he doesn't believe it's lonely. It might just be alone.