Earth's "escape velocity" is roughly 11.2 km/s. This means that if an object is thrown upward at, say, 5 km/s it will fall back to the surface of the Earth. If the object is thrown upward at 7 km/s it will go higher, but still eventually fall back to the surface. If the object is thrown upward at 15 km/s, Earth's gravity will not be able to stop the object and it will never fall back down (it has exceeded Earth's "escape velocity"
Since stars have a lot more mass than Earth, they have higher escape velocities. A black hole is an object whose escape velocity is higher than the speed of light, 300 000 km/s.
Suppose on object has an escape velocity of 330 000 km/s. If someone, somehow, were standing on this objectand were to point a flashlght straight up, the beam of light would go up, slow down, turn around and return to the surface.
Question: Would this be a black hole? If someone tried to observe this from far away, the light from the flashlight would have never made it to the observer, so the object would seem like a black hole, but if they moved closer, they may be able to see the beam of light before it turned around and fell back to the object, so it would no longer be a "black hole".
Does this seem right? Does it matter how far away an object is for it to be a black hole or not?
Are there any astronomers in the house?