Thanks for the question. I’m not at all qualified to give you a great answer for this, but I’ve read my share of popular physics and astronomy books! Black holes are thought to form due to something called ‘gravitational collapse’. This is when the internal pressure of an object can’t fight back against its own gravity – this causes it to collapse inwards (forming a “hole”). The effect of this is that once one has been created, things that get too close cannot escape – not even light!