Can someone fact check my speech about BH?

  • #1
Hey everyone, is anyone able to check the facts of this speech I wrote?
I have 3 minutes max to say this, I might cut out tiny parts to save seconds.
What do you guys think, is this correct? Should I change anything? Thanks!

How Black Holes 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.
 

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  • #2
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In their core, nuclear fusion combines 2 hydrogen atoms into 1 helium atom
That doesn't work.
The reaction has many steps, but the overall summary is 4 hydrogen nuclei (protons) fusing to a helium nucleus. Two of the protons are converted to neutrons in the process.
All of the energy at the core allows the star to fuse heavy elements until it reaches iron.
Only for quite heavy stars.
In a fraction of a second the star collapses under gravity and explodes into a supernova.
The star can't collapse that fast. In addition, only very heavy stars end in a supernova.

I would avoid discussing "sizes" of the interior of black holes or what is inside in general. The first one is not even well-defined.
Since gravity has an effect on space time, if a photon were to pass by the spacetime
Spacetime includes time already - you can't "pass by" it (indicating a change).
if a photon were to pass by the spacetime, it would be warped and enter the Photon Sphere.
The light will fall in. Orbiting in the photon sphere is unstable - every tiny deviation will lead to the light either falling in or leaving forever.
Spinning black holes evaporate due to a process called Hawking Radiation.
Same for non-spinning black holes. Why do you mention the spin here?
Everything you said before only applies to non-spinning black holes but all black holes from supernovae are spinning, it would be better to discuss spin earlier.
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.
That is all wrong. You'll find it in popular science, but that doesn't make it right.
- Virtual particles are called virtual because they are not real. In other words: They do not exist. Virtual particles are mathematical tools in a special type of calculations (perturbation theory).
- Energy is conserved exactly everywhere in quantum mechanics.
- Hawking radiation has nothing to do with virtual particles or particle/antiparticle pairs.
 
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  • #3
haruspex
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A helium atom has at least one neutron, so it will take more than two protons to make one. See
https://en.m.wikipedia.org/wiki/Stellar_nucleosynthesis#Hydrogen_fusion
The heat generated pushes back against gravity, creating the balance. You make it sound as though the balance generates the heat.
The fusion process does not go further than helium at first - the pressures are not great enough. Successive and ever briefer stages of fuel exhaustion and collapse lead to progressively heavier elements.
The actual process of creating helium has two pathways; one involves C, N and O. A first generation star only has H and He at first, so cannot use that, and smaller stars are not hot enough to use it.

I fear this is making your presentation too long, so perhaps better to skip through these details and get to the black holes. Just avoid saying anything false or misleading. More comments later, maybe.
 
  • #4
A helium atom has at least one neutron, so it will take more than two protons to make one. See
https://en.m.wikipedia.org/wiki/Stellar_nucleosynthesis#Hydrogen_fusion
The heat generated pushes back against gravity, creating the balance. You make it sound as though the balance generates the heat.
The fusion process does not go further than helium at first - the pressures are not great enough. Successive and ever briefer stages of fuel exhaustion and collapse lead to progressively heavier elements.
The actual process of creating helium has two pathways; one involves C, N and O. A first generation star only has H and He at first, so cannot use that, and smaller stars are not hot enough to use it.

I fear this is making your presentation too long, so perhaps better to skip through these details and get to the black holes. Just avoid saying anything false or misleading. More comments later, maybe.
Thanks, yeah I am trying to fit in a lot in a very short amount of time so I didn't go super in depth.

That doesn't work.
The reaction has many steps, but the overall summary is 4 hydrogen nuclei (protons) fusing to a helium nucleus. Two of the protons are converted to neutrons in the process.Only for quite heavy stars.The star can't collapse that fast. In addition, only very heavy stars end in a supernova.

I would avoid discussing "sizes" of the interior of black holes or what is inside in general. The first one is not even well-defined.Spacetime includes time already - you can't "pass by" it (indicating a change).The light will fall in. Orbiting in the photon sphere is unstable - every tiny deviation will lead to the light either falling in or leaving forever.Same for non-spinning black holes. Why do you mention the spin here?
Everything you said before only applies to non-spinning black holes but all black holes from supernovae are spinning, it would be better to discuss spin earlier.That is all wrong. You'll find it in popular science, but that doesn't make it right.
- Virtual particles are called virtual because they are not real. In other words: They do not exist. Virtual particles are mathematical tools in a special type of calculations (perturbation theory).
- Energy is conserved exactly everywhere in quantum mechanics.
- Hawking radiation has nothing to do with virtual particles or particle/antiparticle pairs.
Thanks a ton, ill research those problems and fix them!
 
  • #5
Fervent Freyja
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"Black holes eventually die" is imprecise. Dissipate is a better word choice.
 
  • #6
ZapperZ
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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 I were to know nothing about black holes or physics in general, and I listen or read this, I will be very confused. You started off talking about all stars being mainly made up of hydrogen atoms and the helium formation. And then, all of the sudden and without any kind of explanation, you went straight to iron! I would ask "where did this iron come from? I thought it was all hydrogen and helium?"

Zz.
 
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  • #7
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- Hawking radiation has nothing to do with virtual particles or particle/antiparticle pairs.
Isn't that a bit rigorous? Explaining what Hawking radiation is, without usage of the terms 'virtual particles' and 'particle/antiparticle pair' would be quite impossible.
 
  • #8
I have redone the script, using your guys's advice wdyt now?

(Black solid with text saying 40 billion M☉)

40 billion solar masses.

(Cut to me)

That’s the size of the S5 0014+81, the largest known black hole in the universe. But did you ever wonder how they work?


It all begins with Stars. In their core, nuclear fusion combines four hydrogen nuclei into one helium nucleus, releasing an enormous amount of energy in the form of radiation. This energy pushes against the gravity on the star, maintaining a balance between forces. The energy from the fusion allows stars to fuse heavy elements until it reaches iron. Iron does not release any energy when it is fused, so gravity gains the upper hand, breaking the equilibrium. When a very massive star uses the rest of its nuclear fuel, and there are no more reactions to fight the gravity, it explodes as a supernova. If the core remaining is at least 2.5 times the mass of the sun, gravity will eventually collapse the core into a singularity. A singularity is a mathematical point with virtually zero volume and infinite density.

When this happens, it would require a velocity greater than the speed of light to escape the singularity’s gravity. According to Einstein's Theory of Relativity, it is impossible for any object to reach a speed faster than light. Therefore any matter or radiation, including light, that passes within the event horizon of a black hole is trapped forever.

Wait. What was that about the Einstein? (Maybe wear a cutout photo of Einstein as a mask? Or have Einstein as a green screen standing next to me)

In the early 20th century, Albert Einstein published two theories of relativity. The Special Theory of Relativity, and the General Theory of Relativity. But we only care about the general one right now. According to the general theory of relativity, matter and energy bend space and time. Also known as gravity. This is why objects that travel near a large mass will appear to move along a curved path in space-time. Why do we care? To do this theory, Einstein needed a set of formulas called the field equations. This is where Karl Schwarzschild comes in with a solution. The field equations state that an extremely dense ball of matter create a spherical region in space where nothing can escape. Sound familiar? That’s because it is. Using the field equations we know that if we have the mass of a black hole, we can determine the size of the sphere that surrounds the black hole. This is where Karl comes in. The radius of that sphere is called the Schwarzschild radius, and the surface area that surrounds that sphere is called the event horizon. And as we know from earlier, once something enters the black hole, it’s not coming back.

Is there only one type of black hole? Nope! There are three main types that are classified based on their size and mass. The smallest ones are known as Primordial black holes, and are believed to be as small as an atom, but have have the mass of a mountain. Next there are medium-sized black holes. These are called Stellar black holes because their mass can be up to 20 times greater than the mass of our sun and fit into a radius of 8 km. Then we have the champion of all black holes. Supermassive black holes have masses that are greater than 1 million suns and are about as big as our own solar system. Scientists believe that a supermassive black hole resides in the center of all galaxies, including our very own milky way. And that is black holes. I’ll see you in outer space (fly away in a spaceship or jump into a black hole)
 
  • #9
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Isn't that a bit rigorous? Explaining what Hawking radiation is, without usage of the terms 'virtual particles' and 'particle/antiparticle pair' would be quite impossible.
"Explaining it" using these words is wrong. I think a wrong explanation is the worst option. The emission of particles is simply a property of event horizons.
But we only care about the general one right now.
General relativity has special relativity as special case (hence the names). There is no "general relativity without special relativity".
This is why objects that travel near a large mass will appear to move along a curved path in space-time.
A curved path in space but a straight line in spacetime.

It is unclear of primordial black holes exist, and if they exist it is unclear which mass distribution they have.

It is a funny coincidence that the first solution with an event horizon came from someone called Schwarzschild - German for "black shield". An event horizon is "black" and it "shields" whatever is inside.
 
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  • #10
vela
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It all begins with Stars. In their core, nuclear fusion combines four hydrogen nuclei into one helium nucleus, releasing an enormous amount of energy in the form of radiation. This energy pushes against the gravity on the star, maintaining a balance between forces.
You've assumed here that your audience knows that gravity is trying to cause the star to collapse. You should state this explicitly.

The energy from the fusion allows stars to fuse heavy elements until it reaches iron.
This statement isn't right. It's the high temperature and pressure in the core due to the gravitational collapse that allow fusion to occur.

Iron does not release any energy when it is fused, so gravity gains the upper hand, breaking the equilibrium. When a very massive star uses the rest of its nuclear fuel, and there are no more reactions to fight the gravity, it explodes as a supernova.
You're still jumping from hydrogen to iron. If you want to describe how the star evolves, I think you need to describe the process with a little more detail. On the other hand, you might consider leaving all of these details out since they're not really relevant to your topic of how a black hole is produced.
 
  • #11
You've assumed here that your audience knows that gravity is trying to cause the star to collapse. You should state this explicitly.


This statement isn't right. It's the high temperature and pressure in the core due to the gravitational collapse that allow fusion to occur.


You're still jumping from hydrogen to iron. If you want to describe how the star evolves, I think you need to describe the process with a little more detail. On the other hand, you might consider leaving all of these details out since they're not really relevant to your topic of how a black hole is produced.
That's a good idea, I could simplify the start and focus more on cool parts of a black hole like Einstein rings or the photon sphere. Keep in mind I am going to have animations to go along with scenes of just me. So when I say something like it goes from helium to iron, I would have all the other heavy elements it fuses on the screen. Thank you though your tips have been very helpful :). Also do you know any real-life demonstrations I can do about black holes?
 
  • #12
"Explaining it" using these words is wrong. I think a wrong explanation is the worst option. The emission of particles is simply a property of event horizons.General relativity has special relativity as special case (hence the names). There is no "general relativity without special relativity".A curved path in space but a straight line in spacetime.

It is unclear of primordial black holes exist, and if they exist it is unclear which mass distribution they have.

It is a funny coincidence that the first solution with an event horizon came from someone called Schwarzschild - German for "black shield". An event horizon is "black" and it "shields" whatever is inside.
Huh that is an interesting fact, I might include that if I have time! Thanks!
 
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  • #14
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I'd structure this speech completely different for 3 minutes. Not sure why you want to include the part about stars, if the title of your speech is "How black holes work" not how stars work! I'd cut that first two paragraphs out completely, and just use the information after "In the 20th century...". It makes your speech a lot more structured, and you're not as pressed for time. Maybe talk about how we have binary black hole systems, and they helped us first detect gravitational waves (event GW151226)? As far as primordial black holes, I'm not sure if we quite have evidence for them. I don't think that matters to your audience if you present it as fact, unless they're science enthusiasts.

Good luck!
 
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  • #15
PeterDonis
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I'd cut that first two paragraphs out completely
As an alternative if this suggestion is too drastic, you could shorten the first two paragraphs to: "Black holes are formed from the gravitational collapse of stars that are too massive for the collapse to end in a white dwarf or neutron star."
 
  • #16
I'd structure this speech completely different for 3 minutes. Not sure why you want to include the part about stars, if the title of your speech is "How black holes work" not how stars work! I'd cut that first two paragraphs out completely, and just use the information after "In the 20th century...". It makes your speech a lot more structured, and you're not as pressed for time. Maybe talk about how we have binary black hole systems, and they helped us first detect gravitational waves (event GW151226)? As far as primordial black holes, I'm not sure if we quite have evidence for them. I don't think that matters to your audience if you present it as fact, unless they're science enthusiasts.

Good luck!
I totally should cut down on the stars part, it's like 50 seconds of stuff I should cut down to way less, that way I have more time for more important stuff. I will probably include the binary system that sound's a lot better. Thank you!
As an alternative if this suggestion is too drastic, you could shorten the first two paragraphs to: "Black holes are formed from the gravitational collapse of stars that are too massive for the collapse to end in a white dwarf or neutron star."
Thanks as well, I want to include a little bit about stars and how they form black holes because I think that's pretty important, but I totally need to cut down on it.


Here was a revised first paragraph from before I read your guy's ideas.
(How do black holes form?)
It all begins with the Stars. Stars have two basic forces, gravity and thermal pressure. Gravity acts like an energy source that creates large amounts of heat and pressure inside of a star. All this pressure causes the star to begin its thermonuclear fusion process. (Maybe do some cool rainbow word effect of thermonuclear fusion process) This means that inside of a star, hydrogen is fused together to create helium. The fusion creates thermal pressure to keep the star from collapsing under its own gravity, and as long as the star has fuel the thermal pressure and gravity are in a balance called the hydrostatic equilibrium. When most of the hydrogen has been fused into helium, the star begins to collapse as it runs out of fuel. As gravity pushes more, the star begins to fuse heavier and heavier elements until it reaches iron. Iron is the last stage of a star’s fusion because heavier elements require more energy to fuse together, which the star simply does not have. So gravity wins the fight and the star collapses under its own pressure into an explosion called a supernova. (Maybe have a knockout scene against gravity and thermal pressure) If the star has enough mass, then it will collapse into a singularity, a mathematical point with virtually zero volume and infinite density.
 
  • #17
PeterDonis
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Here was a revised first paragraph from before I read your guy's ideas.
You're still describing iron fusion; many stars, including some that will eventually collapse to black holes, never get dense or hot enough to fuse iron in their cores. If you're talking about black holes, I would focus on this: all stars eventually run out of fuel and are unable to hold themselves up against their own gravity. What happens to them then depends on their mass. Stars of low enough mass will end up collapsing to white dwarfs. Stars somewhat more massive will end up collapsing to neutron stars. Stars still more massive than that will end up collapsing to black holes. I would not focus too much on the details of any of this unless you are prepared to get the details right not just about black holes but about stellar evolution and supernovas.
 
  • #18
You're still describing iron fusion; many stars, including some that will eventually collapse to black holes, never get dense or hot enough to fuse iron in their cores. If you're talking about black holes, I would focus on this: all stars eventually run out of fuel and are unable to hold themselves up against their own gravity. What happens to them then depends on their mass. Stars of low enough mass will end up collapsing to white dwarfs. Stars somewhat more massive will end up collapsing to neutron stars. Stars still more massive than that will end up collapsing to black holes. I would not focus too much on the details of any of this unless you are prepared to get the details right not just about black holes but about stellar evolution and supernovas.
Yeah I had read about all the parameters for it to turn into a black hole but I didn't want to add more than I already have. I think I'll cut down a lot on what I said and then add some parts about what it could turn into instead of a black hole. Thanks for your input :)
 
  • #19
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Good luck with your project, Peter. Black holes are fascinating.
 
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  • #20
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I'd structure this speech completely different for 3 minutes. Not sure why you want to include the part about stars, if the title of your speech is "How black holes work" not how stars work!

Good luck!
Agreed, title was total clickbate ;)

joking aside, the context of the "speech" is unclear, so the title is irrelevant. That said I think they asked for fact checking.
 

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