>>12553136A black hole on a gravitational level is exactly the same of the star it is made from (save the mass that was expelled in the explosion generating it).
The only difference is, it doesn't emit light and if you get too close you'll be sucked in, but getting too close to a star would be pretty bad anyway.
So this is exactly equivalent to asking what a passing by star would do to the Earth and our solar system.
If it collided with the sun or the Earth, it would be pretty bad, like, seriously bad.
The problem is even a close passing by could be just as bad, it could disrupt our planets' orbit enough to render the planet uninhabitable.
What could we do? With our current tech pretty much nothing.
