What would happen if a massive black hole happens to enter our solar system?

If a massive black hole were to form close to our solar system, it would destroy everything in its vicinity, including planets and light. If it were to form near the sun, it would destroy the sun and all life on Earth would be rendered impossible.

If Cygnus X-1 or any other star within a few light years ventures into the solar system, it could pull everything inside itself, ripping all the planets into atoms (or maybe even quarks:) The first type would not pose much of a threat until about 4 billion years later, when Andromeda is predicted to collide with the Milky Way.

I hope this is helpful.

To begin with, it is crucial to have a basic understanding of orbits. The Earth and Moon both orbit the Earth-Moon Barycentre (SMB), not the other way around. Similarly, the planets orbit the Solar System Barycentre (SB), not the Sun.

As a massive black hole approached the solar system, its gravity would begin to affect the Sun, the planets, and everything else in the solar system, until everything ended up orbiting the black hole's center of mass, which would be the sun and the planets. Any black hole formed from a large star will by definition have more mass than our entire solar system.

If gravity forced it to happen, some planets would probably be thrown out of the system.

Since black holes are extremely slow eaters, it is likely that asteroids, planets, and comets will break apart to form an accretions disc that will slowly fall into the black hole and begin to emit high energy radiation.

It is highly likely that all of the planets will experience a change in their orbits and distances from the sun, which would be disastrous for life as we know it.