First premise: I have already made this question in the worldbuilding section, but since it is a very specific question many have recommended me to write in the astronomy section so here we are.
Second premise: I'm Italian so please excuse any mistake
So, I'm writing a story about a fast and cataclysmic climate change. Obviously there are some artistic licenses but I would like nothing in my story to be completely impossible, only (at most) very unlikely.
The climate change that I would like to include in my story is very extreme, so I had to discard any terrestrial forcing to cause it (no change of ocean currents, supervolcanoes and methane eruptions) because they could not act fast enough and would not be so catastrophic (compared to what I imagine). So I focused on astronomical forcing. I excluded the impossibly forcing (for example, a magical and radical reduction in solar luminosity) and those that would be more catastrophic than the climate change itself (i.e. a planetary impact).
The last possible (though very very unlikely) option I have left is a dramatic change in the Earth's orbit. I have some knowledge in physics and astronomy so I did a personal search to figure out what could cause such an orbital change.The most plausible option would be to pass a rogue planet (or star) into the solar system, but since I want to complicate my life, I would like the orbital change to happen without any notice, which is quite impossible if it is the passage of a planet or a star in the solar system to cause it.
The only plausible explanations I have found to fully satisfy my scenario are either the passage of a primordial black hole in the solar system (a black hole with Jupiter's mass would have a schwarzschild radius of 2.8 meters and, if it did not come in direct contact with some celestial body, it may take in the solar system without notice) or passing a high-density cluster of dark matter (assuming an self-interacting form of dark matter) near or inside the solar system. Both are immensely unlikely options and very speculative (primordial black holes are hypothetical objects and we still have no idea what the dark matter really is and how it behaves) but I do not think they are impossible in the beginning, or is it wrong?
Assuming I want to move the Earth 2x10^7 km (if I do not mistake at this distance the average temperature of the planet would be between 15 and 18 ° C lower than now) farther from the sun, could this change take place in less than a decade and the earth's orbit would remain stable or simply the planet would be expelled from the solar system?
I also wondered what effects this sudden and drastic lowering of the Earth's temperature would have on the weather (especially considering that the poles would cool down much faster than the equator) but I think it's a pretty OT question so I leave it as optional