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Cosmology and astronomy
Course: Cosmology and astronomy > Unit 2
Lesson 1: Life and death of stars- Birth of stars
- Accreting mass due to gravity simulation
- Challenge: Modeling Accretion Disks
- Becoming a red giant
- White and black dwarfs
- Star field and nebula images
- Lifecycle of massive stars
- Supernova (supernovae)
- Supernova clarification
- Black holes
- Supermassive black holes
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Accreting mass due to gravity simulation
The simulation Sal mentions in the video can be found directly following this video in the lesson.
. Created by Sal Khan.Want to join the conversation?
- What is Critical Mass ?(27 votes)
- The mass after which an object can start performing fusion i.e. the point at which the gravitational force of an object allows hydrogen to fuse into helium.(5 votes)
- in the movie interstellar people go through a black hole, would it be scientifically possible for them to survive ?(5 votes)
- Maybe. If you were to fall into a normal black hole, the tidal forces would stretch you out and tear you to pieces. The black hole in Interstellar is a super-massive black hole that is spinning at about the speed of light. There's a debate in the physics community about what exactly this means, but it's possible that you could fall in without being shredded.
If you're interested, you should look up the work of Kip Thorne. He's an astrophysicist who did a lot of the science for Interstellar.(16 votes)
- Why is it that the moon can change from a pale lemon - to a bright gold - to a red moon?(5 votes)
- Same reason sunsets are colorful and the sky is blue. The atmosphere scatters the light.
At the horizon, light from astronomical objects is passing through at a very slight angle to the surface of the Earth, which means it has more atmosphere to pass through. This causes even more scattering to occur, leaving primarily the longer, redder wavelengths to make it through.(15 votes)
- Does gravity have something to do with the structure of the galaxy?(5 votes)
- I'm pretty sure that without gravity, the galaxy and maybe even the universe would be absolute chaos. I'm not even sure what to expect if we didn't have gravity. Would the moon collide with earth, or would it just float away? Terribly exciting question though!(5 votes)
- What happens when 2 sun's collide?(5 votes)
- usually it wont happen but FYI if it happens an intense grav feild will form which in most of the cases will make a supernova but in some special cases it might form a black hole and no the possibility of forming a larger star is only possible when 2 stars having a really HUGE difference in mass and density collide with each other(4 votes)
- Sorry, I'm new to the whole star thing, what did the red stick represent?(2 votes)
- you can think of it as the axis of rotation
Strictly speaking it is the angular momentum vector of the cloud(3 votes)
- What computer language did Peter Collingridge use to write this simulation? I'd like to work with it offline as well.(2 votes)
- It's the same language KA uses in its videos where you learn programming. I believe it is Javascript.
You can see Peter's code here, and you can also modify it to make your own "spinoff"
https://www.khanacademy.org/cs/challenge-modeling-accretion-disks/1180451277(3 votes)
- what is big bang nucleosynthesis? how it is connected to the formation of elements?(2 votes)
- Nucleosynthesis is the formation of atoms. Big bang nucleosynthesis is simply nucleosynthesis during the big bang.(2 votes)
- What defines a "binary system"?(2 votes)
- it is a two star system(2 votes)
- I can't seem to find the link to the simulation.(2 votes)
- If you go to the Modeling Accretion Disks Challenge, and click on spin-offs, you will find the simulation by Peter.(2 votes)
Video transcript
What we have here is
a simulation, created by Peter Collingridge
in response to one of our computer
science challenge to show how many particles
might interact gravitationally. And the whole point
of the simulation is to get an intuition
for how galaxies form, why they have the
structures they have, how solar systems form, how they
have the structures they have, and how gravity alone can
kind of define that structure. And what's really interesting
about the simulation, besides the fact that it's just
mesmerizing and extremely cool, is it shows the
particles collide. Once they get to a
certain critical mass, you see that they
get colored yellow, maybe to indicate that
there are now a star. Fusion can now occur. And you can zoom in
at different levels to really see how the
different particles or the different
masses are interacting. And then you can actually
rotate that to see a little bit clearer. This is if I'm looking
kind of right on top of it to see how they're interacting. And it's a three-dimensional
simulation, so it's a very rich way
of thinking about these. And what's exciting
for me is it's highly dependent on what
the initial conditions are. In an earlier version
of Peter's simulation, he did not give a net angular
momentum to the system. And so you did not have as
much of the planet satellite or as much of the disk
structures forming. Although right
here, we don't have too much of a disk structure. Although it does
seem to-- there does seem to be a dominant
plane in this scenario. And what's exciting is here
we have a binary system. Sometimes you restart it. You might not have
a binary system, depending on the
initial conditions. You might have
something that starts to look like the Milky Way. Sometimes you might
have something that looks very different
than the Milky Way. And it really gives
us clues of why we see such diversity,
especially when we're looking at galaxies, the
structure of galaxies, that it's highly dependent
on initial conditions. One can argue that
our own solar system did have some net
initial angular momentum because the current
theory, what really catalyzed it was a nearby supernova
that sent a shock wave and allowed the dust that would
form our solar system to reach a critical mass and
start to condense into the sun and the planets. And so this isn't,
at least in my mind, too unrealistic of a scenario. And it's really cool to
look at, and it really gives you a sense of things. You already see you
have a binary star. They're kind of orbiting
around each other, or orbiting around the center
of mass, which kind of looks like around each other. And then this star
right over here has its own kind
of captive planet that is just rotating around it. We can see it a
little bit clearer. If we had a very, at least from
this perspective, a very close range, we can zoom
in a little bit more to see it a little bit better. This has a satellite,
but then they're are also kind of dancing
around each other. So it's a really
fascinating simulation. I could really stare at this
and play with it for days. I encourage you to play
with it, restart it, see how the initial
conditions or what type of solar systems or galaxies
you might end up with. Whether they form disks, whether
you have binary systems or not, whether you have
planets with satellites. And then if you
are more advanced, actually play with
the code, and see if you can really change
the initial conditions, the starting
velocities of things, the number of
particles of things, the distribution of mass that
you start off with, the angular momentum that you
start off with. And see how that might change
the structure of the universes that you create. And I'm going to add an
annotation to this video that links directly to
this simulation, and I'll also put the link
inside of the description. So have fun. I could literally
spend hours with this. It's a fascinating,
fascinating module that he's created where
you zoom in and out. And I really thank
Peter Collingridge for this incredible
contribution.