What would happen if a massive black hole happens to enter our solar system?
We would all die, eventually.
If a massive black hole came up next to our solar system, it would take out everything near it, including light, and planets. If it was by the sun, it would take out the sun, then nothing would be able to grow. That, or it would take out Earth before that.
It wouldn't be a happy ending, though.
Usually black holes fall under two catagories,
The first type wouldn't be much of a threat, until about 4 billion years later when Andromeda is predicted to collide with Milky Way.
The second type could be one threat. Cygnus X-1, or any other star within a few light years could venture into the solar system. It would pull everything inside itself, ripping all the planets into atoms ( or maybe even quarks :)
Hope this helps :)
A massive black hole couldn't enter our solar system as such.
First of all it is important to understand something about orbits. The Moon doesn't orbit the Earth. The Earth and Moon both orbit their centre of mass - the Earth-Moon Barycentre (SSB). Likewise, the planets don't orbit the Sun. The Sun, planets orbit the Solar System Barycentre (SSB).
Any black hole formed from a large star will by definition have more mass than our entire solar system. So, as a massive black hole approached the solar system its gravity would start affecting the Sun and the planets and everything else in the solar system. Everything would end orbiting the centre of mass of the black hole, the sun and the planets.
It is likely that some planets will be flung out of the system if gravity forced that to happen.
Black holes are not gobblers, they are very slow eaters. It is likely that comets, asteroids and even planets will get broken up to form an accretions disc falling slowly into the black hole. This disc could then start emitting high energy radiation.
It is very likely that all of the planets orbits will be changed and their distance from the sun will change. It would almost certainly be catastrophic for life on Earth.