Thats a theory yes! They may me much more common than previously thought and account for the effect described by dark matter.

Well this is all theory but possibly! Could be that two galaxies with overly large black holes merged and the black holes combined. Or maybe the star that force fed this particular black hole was just way larger than normal.

For reference, Sagittarius A*, the supermassive black hole at the center of the Milky Way is 4.3 million times the mass of the sun.

https://beta.nsf.gov/news/astronomers-confront-massive-black-hole-heart

At 30 billion times the mass of the sun this thing is….. big

Ultra massive black holes like this present a problem for science. Accretion disks can only become so hot, dense, and energetic around black holes before they radiate so much energy that they keep themselves from falling into a black hole above a certain rate. There is effectively a limit to how fast black holes can grow.

These super/ultra massive black holes are bigger than it should be possible for them to be, even if they experienced max growth rate constantly from the birth of the universe.

So how did they get that big?

A cool theory is that when the universe was young, dense, and hot, enormous stars formed that were so massive their cores compressed into black holes. And because these black holes are surrounded by a star which is constantly crushing matter into it, the black holes basically get force fed. The accretion disk energy is overwhelmed by the crushing pressure from the gigantic Star.

It’s a fun theory.