John Carlos Baez on Nostr: It's funny that the most massive black hole known is called TON 618. In fact it's ...

It's funny that the most massive black hole known is called TON 618. In fact it's mass is about10³⁸ tonnes. Its event horizon is roughly 400 billion kilometers - over forty times the diameter of Neptune’s orbit. It sits proudly at the center of a distant galazy.

Because it's so huge, its surface gravity is *less* than most black holes. The surface gravity is the force per mass registered by a stationary faraway observer holding the mass right above the horizon via a long string. Surprisingly, this is inversely proportional to the black hole's mass.

For a 3-solar-mass black hole, the surface gravity is half a trillion times the surface gravity on Earth - half a trillion g's.

For the black hole at the center of the Galaxy, it's 3 million g's.

For TON 618, it's just 230 g's. Still damn strong, but much less!

The concept of surface gravity for black holes is a bit weird, and I didn't explain it carefully - but it does make sense, and it's important. The temperature of a black hole is proportional to its surface gravity!

It's explained more here:

https://en.wikipedia.org/wiki/Surface_gravity#Black_holes