Answering the Question

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Del curso dictado por University of Rochester

Confronting The Big Questions: Highlights of Modern Astronomy

272 calificaciones

University of Rochester

Confronting The Big Questions: Highlights of Modern Astronomy

272 calificaciones

An introduction to modern astronomy's most important questions. The four sections of the course are Planets and Life in The Universe; The Life of Stars; Galaxies and Their Environments; The History of The Universe.

De la lección

What Exists Outside our Galaxy?

Galaxies and Their Environments - Galaxy types, Active Galactic Nuclei, Clusters of Clusters of Galaxies

Galactic Zoology6:50

Introduction to Dark Matter3:53

Types of Active Galactic Nuclei4:54

Unified Model for AGN6:09

Galaxy Groups and Clusters6:14

Superclusters6:39

Answering the Question4:29

Conoce a los instructores

Adam Frank
Professor
Physics and Astronomy

Welcome back everyone.

Well so now were at the end of week three

and we're ready to actually answer that question that we posed.

How big is space, what's in it?

So let's think about this, what have we learned?

Well, first of all, we've seen that space is far from empty.

Even though mass is tenuously distributed through

space, there's a lot of matter in space.

For example, there is, within the galaxy, there's what

we call the interstellar medium made of different kinds

of gas clouds of different densities.

And those gas cloud, the gas that's distributed through

space is, there's enough of it for sound to propagate.

So, in space actually, someone could hear your scream if you could scream.

and, of course, they had a receiver to get the right kind of the frequencies.

So not only soundwave but also shockwave

can propagate through these interstellar gaseous medium.

On larger scales, on the scale of galaxies,

we have seen that there's different types of galaxies.

There's spirals and there's elliptical, and then each of

these has a super massive black hole at the center.

So, super massive black holes, 10 to the 6th, 10 to the 7th, 10 to the 8th, 10

to the 9th times the mass of the sun are all out there at the center of galaxies.

And so galaxies and super massive black holes go together.

Something about their formation early on has linked these two

kinds of objects together.

In some cases though, super massive black holes are ejecting

enormous amounts of matter, if enough matter is spiraling inward.

Of course the black hole, anything that falls into the black hole can't get out.

But material around the black hole, that's spiraling inward.

Some of that material can still escape and form

these amazing jets of material that shoot out into space.

Galaxies are not, they don't occur singly, but you actually see galaxies in

groups or in clusters.

And in clusters in particular, the clus, clusters are

large collections of galaxies hundreds or thousands of galaxies.

And there's space, actually there's the intercluster medium as

well, a hot gas that fills the clusters themselves.

You can get the groups themselves, and the clusters themselves, will combine to

form what are called superclusters, and these

are the largest scales of structure in

the universe. They have sort of filaments.

They form themselves into filaments with enormous voids in between them.

So, if we pull back all the way out, what we finally see

is that the universe is a homogeneous, a collection of filaments and foam.

Sort of what we like to think of as the cosmic sponge.

So there's structures all the way up to the supercluster scale

and then beyond that, you finally see a statist, a statistical

homogeneity of mass and its distribution in space.

So, the universe is made up, the matter in

the universe, is made up primarily of dark matter.

80 per 7, 87% of the universe is dark matter, 13%

is normal matter, the kind of stuff we're made out of.

And what that tells you is, we really, it's pretty amazing for all

of our accomplishments, we still don't know what the universe is made out of.

This stuff we call dark matter, we have no

idea what it actually is, we only know, we can only infer its presence

based on things like the motion of the luminous matter that we can see.

The the gravitational lensing, the effect on space

time that we see around superclusters, or clusters, etcetera.

So it's really a remarkable fact that as, as much progress as

astronomy has made, we're still literally in the dark, about the largest constituent

structure, or largest constituent constituents of the universe.

So and finally, if we, you know, look at

all the matter that makes up the observable universe,

what we see is that it covers a space

that is roughly 91 billion light years in diameter.

So there you have it, space is pretty big and it is full of stuff.

And of course, what we're talking about here is the observable universe.

The part of the universe that we

can see that where light has had enough time

since the beginning of the universe to actually reach us.

There is, from what we understand right now,

this is the subject of our next lectures.

cosmologically, we believe that the universe is infinite.

So there's an infinite amount of stuff out there.

And infinite amount, infinite parts of the universe that

we cannot see and we don't know anything about.

Which is a mind boggling idea So okay.

That's it for lecture for our third week.

Now we go on to ask truly cosmological questions.

And that will be where we start next time.

Thank you.

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