> if you replaced the Milky Way's black hole with TON 618 it would appear to be almost as bright as the moon. Does the math check out on this one?

It could be even brighter.

Taking the apparent magnitude of the full Moon and the absolute magnitude of TON 618, then plugging them into a distance formula, gives me a value of over 142,000 light years. That’s about five times the distance between Earth and the galactic centre.

With all the dust and whatnot between us and the galaxy’s supermassive black hole, it’s not outside the realm of possibility that enough light extinction would occur to bring TON 618’s luminosity down to “only” that of the full Moon even if it were 5 times closer to us.

What’s even more extreme than that is by plugging in values for the Sun’s apparent magnitude and TON 618’s absolute magnitude into the same equation, I get a value of over 196 light years. In other words, TON 618 would be as bright as the Sun from 196 light years away.