Question

What physical phenomenon is there that black whole has high gravity

Answer 1

To understand the phenomena at work, you have to understand that gravity is what we call the tendency of one thing to want to get closer to another thing. This “wanting to get closer” is because space (space-time) is like a fabric, like a sheet. If you take a “thing", like a tennis ball, and put it at the edge of the sheet, then take another “thing", like your hand, and push down on the center of the sheet, the ball will roll towards your hand. Now think of big things, like comets, asteroids, moons, planets, and stars. Imagine that they are pushing down on the sheet. They all want to roll towards each other. Notice how much each one pushes down on the sheet. The area of the sheet that is being pushed down and the bit of sheet that is being stretched toward it is what we call the gravity well. The bigger the “thing" the more it pushes down on the sheet. The amount that it pushes down on that sheet is what we call mass. So the more mass something has, the more it distorts the flatness of the sheet, i.e., the bigger and deeper the area of the sheet is being pushed down, thus the bigger the gravity well. Back to our earlier example. Put a tennis ball on the edge and a bowling ball in the center. They both push the sheet down where they sit, but the bowling ball pushes it down further and tugs on more area of the sheet. This makes the tennis ball roll towards the bowling ball. The closer it gets, the faster it rolls, i.e., it's being affected more strongly - experiencing more gravity the closer it gets because the gravity well is getting deeper and more steep. However, if you pay REAL close attention, you see the bowling ball move a teeny, tiny bit closer to the tennis ball because it makes a gravity well too.

Now, we've got space (space-time) which is like a sheet and things distorting it (gravity) and how much they distort it by how much of them there “is” (mass).

Stars are the biggest things there are. Some stars can get so big that they make our Sun look like a grain of sand. The giant stars live violent, often short lived, and have tremendous forces inside them pushing outward, balanced by so much gravity pulling inward. When they die, they explode into the biggest fireworks show in the universe. Once every thing settles, they can no longer push outward. Gravity pulls what’s left in. It pulls the leftovers in so tight that it just crushes everything tighter and tighter and tighter, until something that was once the size of the whole world is now the size of a flea. However, there's still a whole world’s worth of “stuff" there, so even though it's the size of marble, it still presses on the sheet like the bowling ball did.

So, a black hole is when an incredibly massive object (a giant star), can no longer fight against gravity and crushes down into something much, much smaller. It still has an immense amount of mass, its it's just comparatively teeny tiny. It deforms space-time so much that anything that gets too close gets pulled in and can't make it out again, even light.

That's the basic phenomenon. It can get super complex the more you study it, this is the basics.

Answer 2

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