Hey Crazies.
I was thinking lately, I’m an astrophysicist and I haven’t done nearly enough
astronomy videos.
Imposter Syndrome is probably partly to blame.
Stop self-diagnosing, Nick.
Anyway, we’re going to break this pattern right meow!!
Our last video was on nuclear fusion, which usually happens in the cores of stars,
so let’s talk about stars!!!
There is way too much about stars to cram into a one video
so we’ll focus on a specific obstacle:
How do we know anything about stars if they’re so far away and live for millions of years?
By being science ninjas!
HIYA!
Ninjas?
Yeah, ninjas are cool!
It doesn’t have to make sense!
So yes, stars are very far away, but they send out light that travels the distance for us
and that light tells us a lot!
We need two pieces of information: The type of light meaning its color
and the amount of light meaning its brightness.
Contrary to popular belief, color is not a property of matter.
It’s a property of light.
For normal things like you, me, and question clone
our color depends on what light scatters off of us.
Turn off the lights and you don’t see any color.
Stars are different though.
They make their own light.
And the color of that light depends on the star’s temperature.
Let’s take a look at the most familiar star in the sky: the Sun.
It’s what we call a yellow-white dwarf meaning its color is yellowish-white
and its size is modest by star standards.
Or you might say Starn-dards?
Ey?
That yellowish-white color is on its chromosphere meaning “color sphere,”
which has a temperature of about 5800 Kelvin.
Let’s be clear though.
Anything with a temperature above absolute zero is making its own light.
So basically everything.
It just isn’t always visible to human eyes.
Whenever particles nudge each other, a little energy gets lost as light.
What kind of light that is depends on the how fast the particles are going
and, since particle motion tends to be pretty random,
objects with lots of particles emit lots of different kinds of light.
The human body is around 310 Kelvin, so most of the light is infrared.
For a light bulb filament or the Sun, there is a lot more visible light.
But if it’s losing energy, won’t it cool down?
If it were an inanimate object, yes, but it’s not.
The human body uses chemistry to replace that thermal energy.
After all, humans are just sacks of aqueous chemicals.
A star, on the other hand, replaces any lost energy through nuclear fusion in its core.
The temperature in the Sun’s core is 15 million Kelvin,
which is, like, so hot.
Anyway, if you combine the brightness of the star with its color,
you get what we call an HR Diagram.
The Sun is yellowish-white, so it’s right about here on the chart,
but, if we plot a bunch of stars on here at the same time, a pattern develops.
These are the younger stars fusing hydrogen into helium.
These are the older stars fusing helium into larger elements
and these are what are left over after small stars die.
You can draw a stars entire life on this chart.
So, what’s a year in the life of a star?
Basically nothing.
Big stars live for millions of years,
the Sun will live for billions of years,
and little red dwarfs can live for trillions of years.
Stars age so slowly that we’ve only seen a few actually change.
Then how do we know anything about their lives?
Because of that HR Diagram.
We see the patterns in this diagram and combine it with what we know about nuclear
fusion and plasmas to figure out how old a star is.
Then we put the different examples on a timeline to get a full picture.
Oh, right, that’s a great analogy.
Imagine a group of aliens like Milton wanted study the human lifespan,
but they could only spend a few seconds on Earth.
They would show up, take a bunch of pictures, and leave.
Working really hard to piece the pictures together later.
That’s exactly what we do with stars.
Pretty crazy, huh?
So, will you ever look a star the same way again?
Let us know in the comments.
Thanks for liking and sharing this video.
Don’t forget to subscribe if you want to keep up with us.
And until next time, remember, it’s OK to be a little crazy.
In the last video, we learned about nuclear fusion.
Comment response time!
Gastón Astore asked why we don’t shape the Tokamak reactor like an 8 instead of a
circle.
Wouldn’t an 8-shape smash more together at the center?
Well, maybe, but a circle is easier to make.
Not just for the reactor itself, but also the magnetic field.
The reactor uses magnetic force to confine the plasma
and plasma like any other charged particle just naturally travels a circle in a magnetic field.
It’s already a huge challenge to confine the plasma in the first place.
We don’t need to be making it any harder.
Takezo Shinmen was wondering how dangerous hydrogen fusion would be
and the answer is it’s actually really safe.
Sure, the first time we figured it out, we turned it into a bomb,
but that’s what happens when the military funds your project.
Plus you can turn most things that release energy into a bomb,
so that doens't really count as a complaint.
You have to put safeguards in place to prevent explosion,
which is something we already do with the current sources of energy.
The best part about fusion though is that it doesn’t create dangerous exhaust.
It produces helium, which we’re in dire need of anyway for cooling systems.
We actually need the byproducts.
Abu Sayed wanted to know about quantum tunneling during fusion.
OK, so I purposely avoided this in the video.
My videos are already information-dense enough.
Talking about quantum tunneling would have distracted from what I was trying to say,
but we'll talk about it here for a bit.
Hydrogen fusion begins at 13,000,000 Kelvin.
It’s just that, on paper, if you only consider the motion of the protons
you need hundreds of times higher temperatures.
So, we’re clearly missing something if we do that.
If we also consider the protons are quantum particles,
which is exactly what they are.
Then you don’t actually have to break the coulomb barrier.
You just have to get them close enough for the uncertainty in their positions overlap.
Dave Long asked how cosmic rays make things like Lithium and Beryllium.
So, yes, nuclear fusion skips over a few of the early elements on the periodic table,
but fission can come back and make them later.
Fusion is when you combine small elements to make larger ones.
Fission is when you take large elements and break them apart to make smaller ones.
Interstellar space has lots of loose particles zipping around called Cosmic Rays.
It’s a terrible name because they’re particles not rays.
Those particles are moving really fast and occasionally smash into large elements
and the little pieces that break off are sometimes Lithium and Beryllium.
Lots of great questions this time.
Anyway, thanks for watching. See you next time.