December 24, 2019 24

Galactic collisions | Stars, black holes and galaxies | Cosmology & Astronomy | Khan Academy

Galactic collisions | Stars, black holes and galaxies | Cosmology & Astronomy | Khan Academy

In the last video
on quasars, I think I sparked some interest when I
threw out the idea of the Milky Way galaxy actually
colliding with the Andromeda galaxy, which people think will
happen in 3 to 5 billion years. And I threw out in
the context of maybe, maybe the super
massive black holes at the core, the galactic
cores of each of those galaxies will start getting a little
bit more material when that collision happens, and
maybe quasars will happen. I don’t know. But given the interest in
that, what I wanted to do here is kind of an unconventional
thing for the Khan Academy, and actually show a video. And before I play
the video, I have to give credit
where credit is due. This is a supercomputer
simulation made at the National Center for Supercomputing
Applications in NASA, and it’s by B.
Robertson of Caltech and L. Hernquist of
Harvard University. And what I want you to remember,
this is super sped up in time. Just to give an idea,
the amount of time it takes for a star about
as far away as the sun to make one orbit
around the galactic core is 250 million years. And you’re going to see
that this is happening multiple times over the
course of this video. So this video is actually
spanning billions of years. But when you actually
speed up time like that, you’ll see that it
really gives you a sense of the actual dynamics
of these interactions. The other thing I want to
talk about before I actually start the video is
to make you realize that when we talk about
galaxies colliding, it doesn’t mean that
the stars are colliding. In fact, there are going
to be very few stars that actually collide. The probability of a star
star collision is very low. And that’s because
we learned, when we learned about
interstellar scale, that there’s mostly free
space in between stars. The closest star to us
is 4.2 light years away. And that’s roughly 30 million
times the diameter of the sun. So you have a lot more free
space than star space, or even solar system space. So let’s start up
this animation. It’s pretty amazing. And what you’re gonna
see here, so these are just the– obviously–
so one rotation is actually 250 million years, give or take. But now you see these
stars right here are starting to get
attracted to this core, and then they’re actually
attracted to that core. and then some of
the stuff in that core was attracted to
those stars, and they get pulled away. That was the first pass
of these two galaxies. Some stuff is just being thrown
off into intergalactic space. And you might worry maybe
that’ll happen to the Earth, and there’s some
probability that it would happen to the
Earth, but it really wouldn’t affect what
happens within those stars’ solar systems. This is happening so slow,
you wouldn’t feel, like, some type of acceleration,
or something. And then this is
the second pass. So they passed one pass. And once again,
we’re doing this– this is occurring over
hundreds of millions, or billions of years. And on the second pass, they
finally are able to merge. And all of these
interactions are just through the gravity over
interstellar– almost you could call it
intergalactic distances. You can see they
merge into what could be called as a Milkomeda,
or maybe the Andromedy Way. I don’t know. Whatever you want to call it. But even though they’ve
merged, a lot of the stuff has still been thrown off
into intergalactic space. But this is a pretty
amazing animation to me. One, it’s amazing to think
about how this could happen over galactic space scales
and time scales, but it’s also pretty neat
how a supercomputer can do all of the
computations to figure out what every particle, which
is really a star, cluster of stars, or group of stars
is actually doing to actually give us a sense of the
actual dynamics here. But this is pretty neat. This is pretty neat. Look at that. I mean, these are–
every little dot is whole groups of stars,
thousands of stars, potentially.

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