Black holes seem to have captured the imagination more so than all other cosmic bodies or phenomena. Blockbusters like Interstellar and Event Horizon have certainly increased the profile of black holes and worm holes. With a captured imagination comes misconceptions and inaccuracies.
To begin, most physicists believe black holes aren’t even holes at all! Black holes contain matter so compressed that their gravitational pull won’t let their light reach out eyes or telescopes. The reason we know they are there is the effect they have on bodies near them, black holes can cause gases to swirl at speeds close to light giving off high energy radiation that we can see. So a black hole in essence is a compressed sphere of non-reflecting and outrageously dense matter as opposed to a hole.
Black holes can be calculated or predicted using the Schwartzchild Radius formula. This is an object being compressed so far that it’s gravitational pull would pull faster than light. The Schwartzchild radius itself is the distance between the centre of a non rotating black hole and the event horizon.
Another misconception is that black holes rage through the universe sucking in everything in its path. Again, this isn’t entirely true. Black holes do have a massive pull and objects can fall in if they become too close. Otherwise, black holes just sit there. We have a supermassive black hole in the centre of our galaxy, Sagittarius A*. We are all still here with no danger of being sucked in….yet.
So let’s say the sun manages to collapse into a black hole instantaneously, first of all we wouldn’t know until 8 minutes after the event due to the sun being 8 light minutes in distance away from us. The Earth would become very cold and very dark which of course goes without saying.
If the sun compressed itself into a black hole it would be around 3.5 miles in diameter but would still have the same gravitational pull as the sun has now. Signicantly smaller diameter but with the same gravitational force. If the force is the same then the orbit of the planets will stay the same. In essence, Earth would be orbiting the Black hole like it orbits our sun now.
We would not be in any danger of being sucked in whatsoever. The sun itself is not big enough to compress itself into a black hole. Only massive stars become black holes that cause grief and destruction around the universe. If any matter is condensed it can become a black hole, even the Earth itself. If the Earth collapsed into a Black hole it would be around the size of a marble but would again have the same gravitational force Earth has now. It would suck in meteors etc at the same rate. The Moon would still orbit the Earth without falling in or being sucked in.
Even if I collapsed into a black hole I would be one thousand billion billion times smaller than a grain of salt but I would exert the same force as I have now. So nothing would fall into me either.
So what would happen if the Sun became a black hole? I wish I could say that it would cause infinite chaos, hypernova explosions and the total warping of space and time. In reality, the Earth would freeze. That’s about it.