I still can’t get my head around this one. Can anyone help? I know they’re hard even for famous physicists but if anyone can simplify this concept for me I’d so appreciate it! Thank you!
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It’s not a void. There is matter there, and it’s so dense that not even light can escape its gravity. That’s why they appear black – light cannot escape it, and we need light to see it.
It’s not a ‘hole’ in space, it’s essentially a super massive star who’s gravity is now so strong that not even light (photons) can escape it. There is a feature called the Event Horizon, which is effectively a boundary of the black hole. If you cross the boundary, theres no coming back, it’s a one way ticket straight into the black hole.
So basically it’s a 3 dimensional object, just like a star or a planet, but it now has so much mass that it appears as a black hole in space. We can actually see light being bent around black holes because their gravity is so strong.
Black holes are usually what is left at the end of a stars life when the nuclear fusion process runs out of elements to condense into heavier ones releasing energy. Right now its converting hydrogen into helium, then once the helium exhausted it will convert helium into the next heavier element (lithium or something I think?). And it keeps going until iron, where iron cant be converted into a new element AND release energy, it actually consumes more energy to convert. Once this happens, gravity overcomes the the force of the star. In sufficiently massive stars, they will end up collapsing into a black hole.
Typing this as I’m sitting waiting to pick up a friend so no doubt this answer is riddled with problems but I hope I’ve at least hit some points correctly and can give you a better understanding. Check out Kurzgesagt on YouTube, I think they have some neat videos explaining black holes and other massive objects like neutron stars. Happy learning 🥳
Rule 1: there’s no stopping gravity.
Only the biggest stars form black holes, since they are the only ones with enough gravity.
While the star is “alive”, there’s a continuous fusion bomb at the centre, blasting material outwards. When the fuel stops balancing gravity, what does gravity do?
a) For the smallest stars, the red dwarves, gravity isn’t expected to do anything exciting, and the ash just floats away
b) Our sun will end up as a big block of carbon, but the heat and gravity will convert it into a diamond
c) Bigger stars will crush the atoms together. The electrons, normally in a cloud around the nucleus, get pulled in and you end up with a neutron star
d) The biggest stars have so much gravity that the neutrons themselves get crushed into … well, if you know, apply for a Nobel prize. It’s assumed to be a singularity, of infinite mass in zero size. Kinda like the Big Bang, really
Atoms are mostly empty space. Tiny protons and neutrons in the nucleus with tiny electrons going around. If you could remove all the empty space between the electrons and the nucleus the Earth would be the size of a tennis ball.
But gravity isn’t strong enough to remove all that space. The electromagnetic forces keeping electrons away from the nucleus they orbit is stronger than gravity. Even at the center of our sun, with all the weight of the entire solar mass pushing in from all sides, it’s still not enough to overcome the force keeping electrons away from the nucleus.
We’d still need more pressure.
There are some really big ass stars out there. Stars so big that all the weight crushing in from all sides actually is enough to overcome the electromagnetic force keeping the electrons away from the nucleus. Once a star reaches that size the atoms at its core collapse. Then the atoms next to them collapse, and so on.
All of the electrons and protons and neutrons are still there. The mass of the star hasn’t changed at all. It’s as heavy as it was before but it’s packed into a much, much tighter volume. A planet that was orbiting the star won’t be sucked into the black hole, it will continue to orbit it exactly like it had before because the weight hasn’t changed, just the size. It’s not like you see in the movies, consuming everything nearby. It’s not any “hungrier” now than it was before, it’s just that we’ve packed all that gravitational pull into a much smaller area.
Because the size is so much smaller the gravity is much more concentrated. *Gravity decreases proportionally with the square of the distance from the center of mass*. This means when you get twice as far away from the source of gravity you only weight a fourth as much. We can stand on the Earth just fine because we’re 8,000 miles away from the center of the Earth’s gravity. If you stood on a tennis ball sized Earth your head would feel weightless but your ankles would break from the strain.
If there’s enough gravity packed into a small enough area we get a black hole, a gravity so strong that anything that gets close enough to its pull can never escape. Not even light. Even photons, as small and as fast as they are, aren’t able to get away from a pull that strong.
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