Black Holes Explained

https://youtu.be/e-P5IFTqB98


Transcript

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Black holes are one of the strangest things in existence.

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They don’t seem to make any sense at all.

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Where do they come from…

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…and what happens if you fall into one?

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Stars are incredibly massive collections of mostly hydrogen atoms

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that collapsed from enormous gas cloud under their own gravity.

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In their core, nuclear fusion crushes hydrogen atoms into helium

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releasing a tremendous amount of energy

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This energy, in the form of radiation,

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pushes against gravity,

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maintaining a delicate balance between the two forces.

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As long as there is fusion in the core,

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a star remains stable enough.

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But for stars with way more mass then our own sun

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the heat and pressure at the core allow them to fuse heavier elements

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until they reach iron.

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Unlike all the elements that went before,

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the fusion process that creates iron

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doesn’t generate any energy.

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Iron builds up at the center of the star

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until it reaches a critical amount

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and the balance between radiation and gravity is suddenly broken.

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The core collapses.

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Within a fraction of a second,

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the star implodes.

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Moving at about the quarter of the speed of light,

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feeding even more mass into the core.

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It’s at this very moment that all the heavier elements in the universe are created,

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as the star dies, in a super nova explosion.

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This produces either a neutron star,

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or if the star is massive enough,

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the entire mass of the core collapses into a black hole.

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If you looked at a black hole,

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what you’d really be seeing is the event horizon.

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Anything that crosses the event horizon

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needs to be travelling faster than the speed of light to escape.

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In other words, its impossible.

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So we just see a black sphere

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reflecting nothing.

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But if the event horizon is the black part,

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what is the “hole” part of the black hole?

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The singularity.

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We’re not sure what it is exactly.

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A singularity may be indefinitely dense,

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meaning all its mass is concentrated into a single point in space,

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with no surface or volume,

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or something completely different.

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Right now, we just don’t know.

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its like a “dividing by zero”error.

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By the way, black holes do not suck things up like a vacuum cleaner,

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If we were to swap the sun for an equally massive black hole,

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nothing much would change for earth,

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except that we would freeze to death, of course.

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what would happen to you if you fell into a black hole?

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The experience of time is different around black holes,

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from the outside,

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you seem to slow down as you approach the event horizon,

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so time passes slower for you.

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at some point, you would appear to freeze in time,

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slowly turn red,

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and disapear.

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While from your perspective,

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you can watch the rest of the universe in fast forward,

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kind of like seeing into the future.

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Right now, we don’t know what happens next,

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but we think it could be one of two things:

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One, you die a quick death.

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A black hole curves space so much,

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that once you cross the event horizon,

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there is only one possible direction.

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you can take this – literally – inside the event horizon,

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you can only go in one direction.

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Its like being in a really tight alley that closes behind you after each step.

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The mass of a black hole is so concentrated,

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at some point even tiny distances of a few centimeters,

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would means that gravity acts with millions of times more force on different parts of your body.

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Your cells get torn apart,

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as your body stretches more and more,

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until you are a hot stream of plasma,

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one atom wide.

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Two, you die a very quick death.

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Very soon after you cross the event horizon,

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you would hit a firewall and be terminated in an instant.

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Neither of these options are particularly pleasant.

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How soon you would die depends on the mass of the black hole.

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A smaller black hole would kill you before you even enter its event horizon,

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while you probably could travel inside a super size massive black hole for quite a while.

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As a rule of thumb,

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the further away from the singularity you are,

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the longer you live.

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Black holes come in different sizes.

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There are stellar mass black holes,

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with a few times the mass of sun,

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and the diameter of an asteroid.

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And then there are the super massive black holes,

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which are found at the heart of every galaxy,

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and have been feeding for billions of years.

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Currently, the largest super massive black hole known,

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is S5 0014+81.

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40 billion times the mass of our sun.

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It is 236.7 billion kilometers in diameter,

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which is 47 times the distance from the sun to Pluto.

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As powerful as black holes are,

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they will eventually evaporate through a process called Hawking radiation.

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To understand how this works,

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we have to look at empty space.

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Empty space is not really empty,

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but filled with virtual particles popping into existence

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and annihilating each other again.

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When this happens right on the edge of a black hole,

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one of the virtual particles will be drawn into the black hole,

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and the other will escape and become a real particle.

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So the black hole is losing energy.

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This happens incredibly slowly at first,

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and gets faster as the black hole becomes smaller.

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When it arrives at the mass of a large asteroid,

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its radiating at room temperature.

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When it has the mass of a mountain,

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it radiates with about the heat of our sun.

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and in the last second of its life,

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the black hole radiates away with the energy of billions of nuclear bombs in a huge explosion.

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But this process is incredibly slow,

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The biggest black holes we know,

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might take up a googol year to evaporate.

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This is so long that when the last black hole radiates away,

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nobody will be around to witness it.

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The universe will have become uninhabitable,

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long before then.

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This is not the end of our story,

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there are loads more interesting ideas about black holes,

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we’ll explore them in part 2.