Question: what would happen if we replaced the sun with an blackhole

Caroline Roche answered on 24 Oct 2024:

If the sun was replaced by a black hole of similar mass, Earth should continue on it’s orbit as normal. The earth would have to be alot closer (inside the Schwarzchild radius) to be sucked into the black hole. The NASA website says that for a black hole of the sun’s mass that radius would be 3km while the earth is 150 million km away.
But after 8 minutes, we would see no more light from the sun. The moon would also visually disappear from our view as we only see it because it reflects the light of the sun. Plants would no longer be able to photosynthesis and would die in a few days/weeks – some plants and trees would survive longer.
But the temperatures would also start to drop, after a few days the average temperature for the entire earth would be below freezing.
I would expect most life on the surface to die off within a year. Life deep within the oceans or near geothermal activity (where the heat comes from the earths core) would survive for a lot longer, possibly adapting to the new conditions and continuing their lives as normal.