The closest supermassive black hole pair, in NGC 7727, was only recently discovered.
Just 89 million light-years away, these 154,000,000- and 6,300,000-solar-mass black holes are just 1,600 light-years apart.
We’ve also discovered pairs of “double quasars,” with two supermassive black holes each.
Approximately 0.1% of young quasars are expected to be doubles, with typical separations of ~10,000 light-years.
Until 2015, when PKS 1302-102‘s was identified, only one double supermassive black hole was known.
That’s OJ 287, still the most extreme supermassive binary, 3.5 billion light-years away.
First spotted in 1887, it flares with a double burst every 12 years.
Its main black hole is enormous: 18.35 billion solar masses.
Its event horizon is 12 times the size of Neptune’s orbit.
It also has a companion black hole of “merely” 150,000,000 solar masses.
The periodic double burst arises when the smaller black hole punches through the larger’s accretion disk.
With a 12-year orbit, it varies from 0.05 to 0.28 light-years away from the primary.
The secondary black hole precesses 39° with every orbit: a fantastic confirmation of General Relativity’s predictions.
In only ~10,000 years, these behemoths should merge.
Hopefully, humanity will be watching when it happens.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.