How do black holes “consume” light?
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TLDR: while light isn’t affected by gravity, it is still affected by the warping of space time which is an affect of mass.
Have you ever seen one of those [spiral wishing wells for charity?](https://m.youtube.com/watch?v=TzSu14mOvqk)
That’s basically what gravity looks like when you map it onto spacetime. So light goes super fast and normally can just roll up the other side of the wishing well, but if the curve is steep enough on the wishing well due to the extreme gravity of a black hole and the light hits it at too high of an angle it’ll get trapped and basically spin in a circle forever and never leave.
It’s not that it’s affected by gravity, it’s just that spacetime is so warped around large masses that the light spins forever until it enters the singularity. Also remember that warped spacetime due to gravity is what causes time. The more affected warped spacetime is the slower time goes. By entering a black hole the light is entering an area where from our perspective they’re moving infinitely slow. This effect is even noticeable for our satellites because they experience time faster than we do.
Now what happens when the light enters the singularity is a big question because all our math can’t figure out what happens inside a black hole. I’m a fan of fuzzball theory, because it’s a fun name, where everything is broken down into its strings (see string theory) and chained together into a giant ball of fuzz.
Imagine travelling along a straight road that followed the equator, you travelled straight and level but you’d end up back where you started eventually. Space and more importantly time is bent in the same way by gravity, to the light ‘particles’ they are travelling straight but to an observer elsewhere they are being dragged in or around the black hole.
Space can curve.
Space curves into massive objects, so anything going in a straight line will seem to bend toward that object. You can think of light as a car going in a straight line… but the road is banked, so the car driving straight will seem to turn with the road even though its wheels are straight.
A black hole is so massive that the curvature of space near it is like a road banked to the extreme. Any light going outward from the black hole will just bend back in because of that extreme curvature.
Photons aren’t sucked into them. Rather the space they travel through is curved by the black hole’s extreme mass to such extent that what seems from the perspective of the photon to be “going forward” is from our perspective “veering off course.”
Technically everything bends space like that — even you — but just like it takes the mass of this entire planet to keep you moving towards it, so it takes the mass of a black hole to keep a photon moving toward it.
And when photons don’t go into your eye, you don’t see them. (:
The car isn’t steering away from the road; the road itself is bent towards the mountain such that not a single car whose GPS navigates it over that road will ever reach your driveway.
Mass bends spacetime. Black holes are so incredibly massive that they bend spacetime around them so incredibly much, every single direction points to the center of the black hole.
In other words, if you cross the event horizon of a black hole, every direction you travel in thereafter would actually be towards the center. This is true for light as well.
Basically, once you cross the event-horizon, space turns inside-out and the center of the black hole surrounds you entirely.
Black holes don’t really consume anything – they just have a strong gravitational field. That field is not of a different kind than the Earth’s, it’s just stronger. All gravitational fields bend the path of light. Gravity close to a black hole is so strong that it bends the path of light so that no matter what direction the light is traveling, its path will bend back until it is traveling deeper into the black hole. From our perspective far away from the black hole, it ends up looking like there’s a kind of surface that light doesn’t ever come out of, so it appears black. There’s not any material that the surface is made out of, the “surface” is just the distance from the black hole where all light always bends further in.
Because light goes at the fastest speed there is, we know that nothing could ever be fast enough to get out of that black area without its path being bent back towards the center -anything under that “surface” can never come out. That means that we can never learn anything about what is inside of the black hole. Nothing at all can ever come out of it – not light for us to see, nor a person to tell us what was in there.
However, physicists don’t think that you’d notice anything special if you fell through that black surface, called the Event Horizon. You’d just fall along towards the center due to the acceleration from gravity, just like you’d do if you fell off a cliff on earth – only much faster.
TLDR: a black hole is just a place where the gravity is very strong. The gravity is not of a different kind than what we feel here on earth, it’s just stronger.
Simply put, when physics tells you a thing has a 0 value, be that mass, velocity, or charge, that’s a small white lie. The truth is that the actual value of those measurements is so infinitesimal *as to be effectively* 0, but rest assured, **there is a value.**
This pertains to light as well. Blackholes are so ridiculously massive that the amount they bend space time means any light radiation has to bend back towards the event horizon. The escape velocity is faster than light can travel as well, causing a double whammy.
As time also slows down in extreme gravitational fields, to practically a stop, in the case of a black hole, light can’t move even if it wanted to.
Imagine the trajectory of a thrown ball. Imagine a planet, like in the illustrations of The Little Prince of Antoine de Saint-Exupéry, and you throwing the ball from it. If the curvature of the ball throw is smaller then the curvature of the planet and the ball will land on the planet. If the curvature of the ball is bigger then the curvature of the planet it will “fall of” the planet, this is called the excape velocity. If you throw the ball in just the right way, that the curvature fits the planets our ball will just circle the planet (its in orbit). If the planet is bigger you need to throw faster, making the curvature of the thrown ball bigger. But there is a limit of how fast you can throw, that is the speed of light. There is no limit on how big mass (the planet) can get. If the “planet” is so big that the curvature of the ball thrown at fastest speed in any direction is still too small to “fall of” the “planet” than you have black hole. Because this also results in any “balls” thrown from a different planets (suns etc) not being able to bounce off our black hole, so all light (“balls”) “stays” on our imagainary blackhole-planet. If no balls (photons) can come or bounce off our big planet, we percieve it as black. (I know its not a precise explanation but its ELIF)
With Einstein’s understanding of gravity, mass curves spacetime rather than ‘attracting’ things. Near a black hole, the gravity well is strong enough that the curvature of spacetime only leads toward the black hole. Light is following a straight path through curved spacetime.
Black holes have so much mass that you need to exceed the speed of light to escape their gravity well.
On earth, we need to accelerate a craft to over 11.2km/s to escape the pull of the planet’s gravity.
Light travels just under 300,000km/s. The escape velocity is faster than that, and so, nothing comes back out because that 300,000km/s is the universe’s speed limit as we know and understand it.
Light just travels in a straight line following the curvature of space-time. That curvature is so great beyond the event horizon that it may as well be twisted into a knot. Light follows that curve and gets “stuck”.
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