Do Solo Black Holes Roam the Universe?

If you were to take the 3 million solar mass black hole in the center of the Milky Way, and plop it into the solar system where the sun is, the Schwartzchild radius would be well within the orbit of Mercury. We wouldn't lose a single planet, though an earth "year" would shrink to roughly 2 hours. Hold your fist at arm's length. That's how big it would appear in the sky.

Now imagine trying to see something like that, from 4 billion light years away, moving faster than galactic escape velocity. The only reason you can see it at *all* is that it's still siphoning galactic gas into its accretion disk. Once it hits intergalactic space, you'll never see it again.

Three million solar masses sounds huge, but is a microscopic fraction of the Milky Way's total mass (1-4 trillion solar masses). Given the quantity of matter orbiting near the center of a galaxy, I'd believe it likely that even if the central black hole were ejected, a new one would form in short (cosmologically speaking) time. So core ejection may not be a one-off, but a common event during galaxy collisions. In which case, there might be enough of them to partly explain dark matter (though certainly not enough to explain it all).

We also know there is a relationship between the mass of the central black hole, and the "tightness" of the arms in a spiral galaxy. But how would core ejection affect this? Given the speed of light, the outer regions of a galaxy would be tightly wound, while the inner region would be loosely wound (after core ejection). Wouldn't that look an awful lot like a barred spiral?

So many interesting questions, so few answers...

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