Yesterday we learned about the active galactic nuclei and what they are and just as a very brief summary I wanted to mention a few of the facts.

As well today look at other things concerning this active galactic nuclei.

Especially, I mean one of these main characteristics is they actually look like normal galaxies if you look at them in the optical with an actually very just bright center maybe.

But other than this, this looks like normal galaxies in the optical.

Then I also mentioned, talked a lot yesterday about the center of these galaxies radiates strong also in X-ray energies and this is because in the center there is a supermassive glycol.

And this is how we imagine these systems. So we have the supermassive glycol in the center surrounded by an accretion disk where matter forms and then disk which is then accreting onto the glycol and this produces a strong X-ray radiation as well.

And yesterday I told you a lot of interesting facts about what you can actually measure that you can actually measure the spin of these objects by studying these very inner regions around the black hole in X-ray energies.

But what we have so far completely left out are that a lot of these objects show very strong chats and what I mean by these kind of chats I'll explain in a few minutes.

So now we're not looking at the central part anymore but more onto these chats from this active galactic nuclei.

And at least as the weather is covered these chats were seen in radio wavelengths so meaning rather not so high energetic photons.

So here in the center I showed this yesterday as well you have the optical of the galaxies and this is the very core of the active galaxy and then you see really large lobes which are very bright in radio.

So this is an overlaid image so you can see the optical and the radio and you can see the large extent of these radio lobes.

So I guess from this picture it's clear that something quite extreme has to happen here in order for I mean this is a large galaxy already and you have huge lobes of radio emission around there.

So some mechanism needs to be there inside probably connected to the black hole in the middle somehow because this is the only way how to produce these energies in order to create such structures.

And we'll have a look at this one by one how these are created and how they are connected to the core.

First what you do as an astronomer after you look at the picture you're looking at the spectrum of such an object or at least of part of an object.

And so this is an energy spectrum of what you would expect of what you see exemplarily shown if you're looking at these radio emission here and this now concentrating just on one part of these radio emissions as we call this of just one blob of this emission.

And so this is so this is the frequency and we're going down here into the radio.

And what you can see is that you have a power law in both directions so what's the high energies that falls here.

And here one says it's absorbed because it's also going down here to the left side. So this is just one spectrum of such a radio emitting blob. And what we know is that this is coming from synchrotron radiation.

So this is electrons spiraling in the magnetic field somehow producing this radiation and we know this because this is the only way so this is polarized radiation.

So the vector of the field when you measure it is aligned and this is only possible in such a way in a synchrotron effect and not in kind of the compensation I talked about yesterday which is happening very close to the black hole.

It's a very chaotic process is a thermal process. So you can't align your vector here so well so you don't get any polarization at all from this compensation I talked about yesterday.

So this has to be a different process and it's also very much low energies here.

Yes. So this is what we expect or what we also observe from one blob of this emission.

If you're now looking at the actual spectra you observe from these sources.

So you can see that they're actually getting more complicated. So those are four example spectra so that you can compare this to the previous image and you see that they don't actually look that much.

Maybe this one also falls down into lower energies and the high energies but otherwise those look very different.

More or less the different classes of these objects we see in active galactic nuclei. So they don't all look the same if you look at these objects or at the jets of these objects.

So I can briefly explain what these are. So you have something like you say steep spectrum sources are extended here. You can see an NGC 1275 which is going down here.

And then here because it's turning over it's just you can't see this here anymore because it's maybe shifted in frequency because the synchrotrons radiation is self-absorbed here.

And once you look at maybe a larger jet where you can superimpose several of these regions you end up with a more flat spectrum.

So you can imagine this here on the right is composed of three spectra just added up next to each other because you're not looking at a single blob but from several blobs.

And this is what you would call a flat spectrum source, a flat spectrum radio quasar in this sense.

This is kind of to illustrate well we have quite energetic phenomena but if you look at them as a spectrum in order to find something out there at least they're different.

So we have to somehow classify them and just very briefly want to explain what these different classes of radio galaxies are we have.

So and I'll show a few pictures of those later I'll explain it now just in the list.

You have powerful double-lobed radio galaxies this was the picture you saw before and those have a steep radio spectrum which is falling towards the higher frequencies.

You have weaker steep spectrum sources with double-lobed with also where you see the double-lobed but you don't have a hot hotspots.

As I said I'll show the picture maybe best now.

So those are the ones which are the phenomena for all in one type.

Those we call double-lobed because you see on both sides a jet but you don't see any hotspots the leading hotspots.

So these are called the phenomena for all in one galaxies.

This is also an example of a phenomena for all in one.

So you see radio lobes in both directions but you don't see any hotspots here and by hotspots I mean something like this.

So this is now a phenomena for all in two type galaxy.

You have lobes on both sides but you do see clear hotspots here.

And the important difference is that they are often one sided so you see one jet here at this side and no jet at the other side.

I'll explain later when we talk in more detail why this is the case because we also understand this.

Both of these sources have a spectrum which is more or less a steep spectrum sources which is falling towards higher energies.