peter wrote:I'm a bit confused; I heard a scientist on TV when asked what exactly a black hole was, answer with a laugh. It's quite simple, he said, a black hole is an object of such huge mass that nothing, not even light, could escape from it's gravitational pull.
Does that mean that a black hole is a lump of matter, a dead star or the like. I thought a black hole was a singularity; a place where the gravitational force had become so intense that the matter had actually collapsed in upon itself to a point of infinite smallness, but infinite mass. A pinch-point where you could be drawn in and spun out to .......who knows where? That bit in films where they always show like a tube of swirling stretchy colours, not a regular workaday hunk of stuff, of bog standard matter? Tell me it isn't so!
A black hole is just an object (like a baseball or whatever) with its mass confined to such a small area that it's gravity (which is inversely proportional to radius squared) becomes strong enough to "suck in" light. Any light lucky enough to not be too close gets bent around the object (gravitational lensing). The matter is confined to a single point called the singularity (although there is debate among physicists if it is a literal 1 dimensional point or just a lump of ultra-dense matter.
In the real world, the black hole forms from stars since they're the only objects in the universe that can naturally collapse to form a black hole (you need enough matter so gravitational force overcomes opposing forces such as gas pressure, electron repulsion, etc). Basically the star collapses forever if its matter is collapsing into infinity.
That dark sphere you see in the photo (black holes are 3D) is actually the shadow of the singularity, called the event horizon. That's the point at which the light can't escape. The bright edges are the points where light can
just escape. The light is generated from the matter being so close that it "rubs off" their electrons, generating the plasma, which glows.
You know how metal glows brightly when it's heated? Same principle.
Going back to the equation I referred to, I guess you could wonder if the gravitational force will become stronger and stronger on its own without matter being fed to the black hole since technically gravity acts on objects an infinity distance away from the object (Newton's laws). The object is collapsing infinitely, so it's radius is infinity. I would say (and I might not be accurate here...it's not my profession) that the math would work out something like how 1/infinity = 0.... Basically you wouldn't get any appreciable difference in gravity so you could say it remains constant (disregarding Hawking radiation causing the black hole to evaporate over an eternity) if matter is not fed into it. Obviously, the singularity becomes heavier with more mass added to it from devouring nearby stars, gas clouds, planets, etc. So its gravity will grow as well, although not in any appreciable sense for a supermassive black hole like TON (largest BH in known universe) or M87. They would grow a lot more if they devoured other black holes.
especially if the pics are even more impressive.