There's never a dull moment — er, light year — in outer space.
NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton spotted an unusual X-ray signal in the data received from the Perseus galaxy cluster some 240 million light years away.
The signal appeared as an intensity spike at an X-ray wavelength where none had been seen before.
So what is it? Is it lovable '80s sitcom star Alf returning to Earth to provide us all with four more seasons of his hilarious show and possibly star in a made-for-TV movie?
Alas, probably not. Though the origin of the signal is not yet known, one of the possible explanations has scientists pretty pumped up. The signal could have originated from the decay of sterile neutrinos, particles that some experts have proposed as the source of dark matter.
Dark matter is believed to make up 85 percent of the universe. However, because it doesn't emit or absorb light, it can't be seen or even proven to exist.
There may be other less exciting explanations. Time will, hopefully, tell.
"More data and investigation will be needed to confirm both the signal's existence and nature," NASA reports.
The mind boggles.