Supermassive black holes may solve mystery of our universe's gravitational-wave 'hum'
NANOGrav made the first detection of low-frequency gravitational waves this year. Now, the hunt is on to find the source of these ripples in space — and supermassive black holes are lead suspects.
TroibNews 
NANOGrav made the first detection of low-frequency gravitational waves this year. Now, the hunt is on to find the source of these ripples in space — and supermassive black holes are lead suspects.
