Can someone check these facts?

[AviSchiffmann]

Hey everyone, is anyone able to check the facts of this speech I wrote?

It's about the Schwarzschild radius and Spaghettification.

Thank you so much!

Black holes are an extremely heavy region of space where all sorts of crazy things happen in physics. To make a black hole, you need a lot of mass crammed into a very small amount of space. Imagine cramming the entire Earth into a ball you could fit into your pocket. One of the essential ways a black hole can be formed, is by having an amount of mass, say a star, and compressing it until it reaches the tipping point, collapsing into a singularity, the center of a black hole. This is called the Schwarzschild radius, and it is the formula that explains how far you need to compress an object until it reaches its tipping point and collapses into a black hole. To find the tipping point we need the Schwarzschild's radius formula. The size of Schwarzschild's radius solely relies on the mass of the object, the rest of the numbers in the formula are all constants. So the more dense you make the object, the larger the Schwarzschild's radius will be. That means that if I were to compress the Earth to the size of a peanut, the Schwarzschild's radius would be quite small because a peanut is only a few centimeters large. But if you had a much bigger object, say an extremely dense star, the Schwarzschild's radius would be a lot bigger because the mass is much larger. You can figure out the tipping point of anything, even yourself. Our sun has a Schwarzschild's radius of about 3 km, our earth, just 1 cm. But what about you? Since the other numbers besides mass in the formula are constants, we can rewrite it as 1.49*10^-27. I weigh 54 kg, so if I plug my mass into the formula, I would need to be compressed into 8.02*10^-26 meters. That's 0.00000000000000000000000000802 meters. Because compressing something that small takes so much energy, it would be near impossible for this to ever happen, but not for stars with very large masses. When a very massive star collapses in upon itself, it causes a supernova. The massive amount of energy from the supernova causes stars to be compressed way past the Schwarzschild’s radius, causing them to form a singularity. The gravitational pull from the singularity is so great, that not even light can reach the escape velocity once it passes the event horizon.
But what would you see if you fell into a black hole?
As you are pulled in, space and time would warp around you, and by the time the black hole filled half your vision, you would be in the Photon Sphere. At this point, the photons in light actually orbit the black hole. When you finally cross the event horizon, things would begin to hurt. As you inch towards the singularity, parts of you that are closer would be pulled more strongly. This is because the closer you get to the singularity, the more the gravitational forces begin to have an effect on you. Your entire body would be stretched towards the singularity with extreme forces. The molecules inside of your body would be ripped and stretched apart until you are nothing but a string of atoms adding to the mass of the black hole. This is a process called Spaghettification because the forces pulling on the object would stretch it into long thin shapes that resemble spaghetti.
 

[mathematic]

Quote

But what would you see if you fell into a black hole?

Current physics theory cannot answer this question. 

(I didn't read the rest of your note.)

Edited June 7, 2018 by mathematic
typo

[Strange]

Generally pretty good. There are a few bits that are potentially confusing or misleading...

16 hours ago, AviSchiffmann said:

Black holes are an extremely heavy region of space

Heavy is an odd word to use (heavy is how we describe weight - i.e. the effect of gravity on mass). But then again, it is hard to think of a better word. Dense would be even more wrong! 

I guess what you want to say is something about a large amount of mass in a small volume....

16 hours ago, AviSchiffmann said:

having an amount of mass, say a star, and compressing it until it reaches the tipping point, collapsing into a singularity, the center of a black hole. This is called the Schwarzschild radius

It is not clear what the Schwarzschild radius refers to in this sentence. It reads as though it is the singularity, but that has zero size. So, I guess it is the "tipping point" that is the S. radius but that isn't clear from the sentence.

16 hours ago, AviSchiffmann said:

So the more dense you make the object, the larger the Schwarzschild's radius will be.

The more massive you make the object. One of the counter-intuitive things about a black hole is that the average density decreases as they get more massive. (Because the radius is proportional to the mass, the volume is proportional to mass cubed. Therefore density decreases as mass squared.)

16 hours ago, AviSchiffmann said:

That means that if I were to compress the Earth to the size of a peanut, the Schwarzschild's radius would be quite small because a peanut is only a few centimeters large.

The Schwarzschild radius depends only on the mass, not how much you compress it. The S.radius of an Earth mass black hole is just under 1 cm, which is a bit bigger than a peanut!

There is a handy calculator for these things here: http://xaonon.dyndns.org/hawking/

16 hours ago, AviSchiffmann said:

When you finally cross the event horizon, things would begin to hurt.

Again,this depends on the size of the black hole. For small black holes you might be torn apart before you reach the event horizon. For very large black holes you would hardly notice anything until after you have passed the event horizon. 

20 minutes ago, mathematic said:

Current physics theory cannot answer this question. 

Well, it can. We just don't know if it is correct or not!

http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/fall_in.html

[beecee]

24 minutes ago, Strange said:

 

Well, it can. We just don't know if it is correct or not!

http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/fall_in.html

Here's another..

http://jila.colorado.edu/~ajsh/

[AviSchiffmann]

3 hours ago, Strange said:

Generally pretty good. There are a few bits that are potentially confusing or misleading...

Heavy is an odd word to use (heavy is how we describe weight - i.e. the effect of gravity on mass). But then again, it is hard to think of a better word. Dense would be even more wrong! 

I guess what you want to say is something about a large amount of mass in a small volume....

It is not clear what the Schwarzschild radius refers to in this sentence. It reads as though it is the singularity, but that has zero size. So, I guess it is the "tipping point" that is the S. radius but that isn't clear from the sentence.

The more massive you make the object. One of the counter-intuitive things about a black hole is that the average density decreases as they get more massive. (Because the radius is proportional to the mass, the volume is proportional to mass cubed. Therefore density decreases as mass squared.)

The Schwarzschild radius depends only on the mass, not how much you compress it. The S.radius of an Earth mass black hole is just under 1 cm, which is a bit bigger than a peanut!

There is a handy calculator for these things here: http://xaonon.dyndns.org/hawking/

Again,this depends on the size of the black hole. For small black holes you might be torn apart before you reach the event horizon. For very large black holes you would hardly notice anything until after you have passed the event horizon. 

Well, it can. We just don't know if it is correct or not!

http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/fall_in.html

5

Thanks so much this is really helpful! Do you recommend I talk about Spaggehtification at the end or more about the Schwarzschild's radius?

[Strange]

12 hours ago, AviSchiffmann said:

Thanks so much this is really helpful! Do you recommend I talk about Spaggehtification at the end or more about the Schwarzschild's radius?

Well, I guess you want your talk to end with some drama so I would end with spagghettification. It may be worth noting that this is actually just an extreme form of the tidal forces that raise sea levels on opposite sides of the Earth (and lower them in between. So we are constantly being a tiny bit spagghettified by the Moon. It is just that a black hole can take this to a whole new level!

[beecee]

19 hours ago, AviSchiffmann said:

Thanks so much this is really helpful! Do you recommend I talk about Spaggehtification at the end or more about the Schwarzschild's radius?

The spaghettification effect is caused by the tidal gravitational effects...the difference in the pull of gravity on your feet compared to the pull on  your head, to use the familiar analogy that the great Stephen Hawking used. This effect continues to increase as one approaches the center of the BH, until in effect all matter is broken down into its most basic fundamental parts like quarks etc...in other words as one approaches the center even the strong nuclear force is overcome. All to the best of our knowledge of course, and current physics that we know of.

[Scott of the Antares]

23 hours ago, Strange said:

http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/fall_in.html

 

Strange, that was a great read. Thank you for posting it here!

[AviSchiffmann]

Hey guys I updated my script and changed a bit, what do you think now?

Black holes are one of the weirdest things in space. They can warp space and time, and even swallow up entire stars! But did you ever wonder how they created and work?

Stars are massive collections of mostly hydrogen atoms. In their core, nuclear fusion combines 2 hydrogen atoms into 1 helium atom, releasing an enormous amount of energy. This energy pushes against the gravity on the star, maintaining a balance between those two forces and creating heat. All of the energy at the core allows the star to fuse heavy elements until it reaches iron. But iron is special, unlike the other elements it doesn’t release any energy when it is fused, so the iron builds up inside the core until the balance between gravity and energy is broken. In a fraction of a second the star collapses under gravity and explodes into a supernova. If the star is massive enough, the core will collapse into a singularity, the center of a black hole. But if the star is not big enough, it will instead turn into a neutron star. The boundary surrounding a black hole is called the event horizon, once you enter it, not even light can escape. You would need to have an escape velocity higher than the speed of light to break out, and according the Einstein's Theory of Relativity, that is impossible. The size of an event horizon is based upon the Schwarzschild radius, which states how much mass needs to be compressed for the gravitational effect of that mass to be so strong that even light can’t escape. For example, the sun would need to be compressed into 3 km, and for the earth, the Schwarzschild radius is even smaller at about 1 cm. Although, light doesn’t necessarily have to enter the event horizon. There is a really wonky place called the Photon Sphere, which is 1.5x the Schwarzschild radius, where light itself actually orbits a black hole. The gravity that pulls the light in is just as much as the momentum that carries it away from the black hole. If you were to find yourself in the photon sphere, you could look sideways and actually see the back of your head because the photons reflecting off the back of your head would travel all around the black hole right back to your eyes. But if photons have no mass, how do they orbit a black hole? Since gravity has an effect on space time, if a photon were to pass by the spacetime, it would be warped and enter the Photon Sphere. Black holes eventually die, just like most things in the universe. Spinning black holes evaporate due to a process called Hawking Radiation. To understand this we have to look at what is called “empty space”. Empty space isn’t really empty though, it is filled with virtual particles that pop into existence. In quantum mechanics, temporary violations of the conservation of energy can occur when one particle can become a pair of heavier particles, what we call virtual particles, that quickly rejoin the original particle as if they never existed. When this happens at the edge of the event horizon, one of the virtual particles will be drawn into the black hole, and the other one will be shot out and turned into a real particle. Therefore Hawking radiation causes the black hole to lose energy and mass, which ultimately causes it to evaporate.
 

I have a speaking limit of 3 minutes btw

[Janus]

14 hours ago, AviSchiffmann said:

 But iron is special, unlike the other elements it doesn’t release any energy when it is fused

Iron is not unique in this respect.  Any element above Iron on the Periodic table also requires a net input of energy in order to fuse.  Iron marks off the boundary between elements that produce energy through fusion and those that consume it.

 

14 hours ago, AviSchiffmann said:

If the star is massive enough, the core will collapse into a singularity, the center of a black hole.

We don't really know if a singularity actually exists at the center of a black hole.  All we know is that if enough mass is left over after the Supernova, it will collapse until it is smaller than its Schwarzschild radius.