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I thought I'd talk about NGC one well let's show you a picture of it first here it is this is NGC one it's a nice looking spiral galaxy one might many other spiral galaxies but you know quite a pretty spiral galaxy nice bit of star formation going on which you can see in the kind of the blue young stars in its outskirts here so nice spiral galaxy it's reasonably distant it's not a huge distance away all the NGC galaxies are not ridiculous distances away because actually they're you know relatively nearby bright Galaxies for the most part okay so I guess we need to start with the NGC bit NGC stands for the new general catalog as with many things that are called new it isn't new
anymore it was new when it was made so it was actually made sort of the end of the 19th century and it was called the new general catalog because it replaced the general catalog which was the catalog that preceded it and so here is the paper it's a new general catalog of nibly and pluses of stars being the catalog of the late Sir John F W Herschel bought revised corrected and enlarged and it was made by this chat John Dreyer who was a Danish astronomer but actually spent most of his career working in Ireland uh both in the South and the Northern Ireland at different times so John Herschel was William herschel's son so William and Caroline Herschel kind of did the first go at
collecting a catalog of galaxies and star clusters or nebulae as they were then called because they didn't know they were galaxies and then his son John kind of took over made a whole lot more observations actually did a lot of observations from the southern hemisphere because obviously there's a whole lot of other galaxies that you can't see from the Northern Hemisphere to kind of increase the size of the catalog John then put together this catalog of star clusters and nebulae called the general catalog which this was kind of intended to supersede it turned out there were lots of problems with the general catalog um in fact there's some wording here let me see if I can find the wording here he's a little bit rude about it
somewhere in here if I can find the wording although the probable errors of results are much more the observations of the two Herschel so that's the Father and Son which naturally arose from the construction of their instruments and the haste with which the observations often necessarily were made there are therefore many cases where the general catalog although evincing the most scrupulous care both in observing and reducing is not in accordance with the heavens one which is you know kind of the nature of these things that you really want your catalog to say where the galaxies are and you know what type they are and so it's a it was a yes it's quite a subtle dig in that you're saying you know they took a great deal of care over
it but they still messed it up from time to time so the new general catalog isn't so much a tweak of the general catalog it's more of a reboot is it pretty much so it took the general catalog it added a whole bunch of observations that other people have made sometimes those are other observations were correcting things from the general catalog other times they were completely new observations and produced this completely new catalog having said that the new general catalog also has a whole bunch of errors in it there are some places where it says there's a nice big bright Galaxy here and if you point the telescope there's nothing there at all so some errors necessarily propagated through um but it's kind of an improvement on it
it's much larger it's about eight thousand almost eight thousand objects in total galaxies are still known by their NGC numbers today so typically if it's a nearby bright Galaxy it'll have an NGC number and that's sort of the usual name that's used to describe the Galaxy just for deep sky videos viewers where does the Messier catalog that they will be very familiar with by now fall into this that's older isn't it much older so that's sort of 18th century so this is the end of the 19th century so hunt more than 100 years later some messier objects are in the NGC I think most of them probably are actually because they're all kind of big bright nebulae um so they will have an NGC
number as well but you know the Messier catalog is 100 or so objects this is you know almost 8 000 objects and then having done that he found he missed a whole bunch of galaxies and actually while he was compiling it more and more galaxies were being found this is kind of this was happening at sort of the birth of photographic astronomy so people were finding much fainter galaxies than they've been able to find before and so there is a whole sort of supplement to the NGC that Drea came up with called the index catalog so quite often you'll find galaxies called I see something or other and they're from this sort of supplement to the NGC um that the dryer came up with of
subsequently it's kind of at the very beginning of the 20th century I've I thought Dreyer should be a really big name then I've heard of Herschel I've heard of Messiah I'd never heard of Draya before he is surprisingly not yet not that well known because I mean I guess because his main claim to fame is that he just compiled these catalogs and that's not really the thing that kind of gets you the big profile in astronomy right he wasn't making the great discoveries for himself he wasn't out there making the observations for himself mostly he was just compiling this catalog so you once you've decided you're going to make a catalog you have to decide what order you're going to put
the galaxies in okay and the way they're arranged in the NGC is they're arranged by right Ascension so right Ascension is kind of the astronomical equivalent of longitude it's measuring where in the sky things are and so basically you store some particular sort of longitude on the sky and then you go east from there and East in astronomical terms East is to the left not to the right because if you think about it if you're lying on your front and your head's pointing North then East is on your right that's kind of people where people think East or to be but if you're lying on your back looking up at the sky with your head pointing North then East actually on your left and so the East kind of increases to the
left on the sky so basically you start at this particular line on the sky and then you work your way around the sky towards the east so towards the left and where is this line drawn where is this prime meridian of the space it's kind of arbitrary but it's to do with where the sun is at the Equinox suffice to say it's kind of you know you could have picked any point just as you know prime meridian ends up going through Greenwich you could have picked anywhere on the earth we could have picked anywhere on the sky we pick a point on the sky that's related to the equinoxes and the solstice and so basically it means that the NGC one so zero on this scale is overhead in the middle of the day in springtime or in the middle of the night
in Autumn time okay so if you want to observe NGC one then September is the time to observe it because that's when it's visible in the night time and does NGC one sit right on the line pretty close to the line so the other issue is that actually we have to keep changing these coordinates a bit because the axis of the earth wobbles around a bit that means that our kind of definitions of this zero point kind of changes over time so you have to keep processing the coordinates or changing the coordinates a little bit which means that something which is exactly on zero at one Epoch a bit later on won't be exactly on zero anymore so it's not actually exactly on zero anymore but so here it is this is NGC one
and in fact this guy here which is just a little bit further to the east is ngc2 turns out to be very close to it on the sky it needn't have been it could have been halfway across the sky and a bit further away but it just turns out then they're completely unrelated they're completely different distances but it just happens that in terms of how you know this is a tiny bit further to the use than this guy so this is NGC one and this drives engine I was going to talk a little bit about NGC one and actually it sort of fits with the question of why people bother to collect these huge catalogs in the first place what's the point you know why is somebody gone because so who was it rather than firmly
said famously said all science is either physics or stamp collecting and this is clearly stamp collecting right it really is and so the question is why do people dedicate their lives to stamp collecting and the answer is it's absolutely critical for doing science with and there are a whole bunch of science that you can only do once you've actually collected one of these catalogs and understood the galaxies in it and you've got this you know wide array of galaxies that you can now choose from so you can actually pick the galaxies that are interesting that have the properties you're actually interested in I want to give an example about it which actually NGC One features in which is a paper that came out a couple of years
ago it's called larger Lambda R in the disk of isolated active spiral galaxies than in their non-active twins what these guys did is they were interested in trying to so some galaxies are active which means they have a black hole in the middle which is doing stuff it's making it very bright it's throwing out Jets and material whatever the black hole in the middle is doing something dramatic and what they were interested in doing is saying is there some property of the Galaxy that makes some things have these bright nuclei these active Galactic nuclei and others not if you're going to try and do that what you want to do is you want to find a sample of active Galactic nuclei so
galaxies that have these antibalactic nuclei and then you want to find another bunch of galaxies that look as much like them as you possibly can just their twins and then you say okay so I've picked this galaxy to be as much like this galaxy as I can but are there still any kind of systematic differences between the two which might explain why one of them has an active black hole in it and the other doesn't and so that's exactly what they did so here is a couple of their galaxies so NGC 2906 is a galaxy with an active nucleus it's not a particularly bright one it doesn't look very dramatic in this picture but it does have an active black hole in the middle of it and so they then went through they found maybe
a dozen of these galaxies and then they look for their twins and it turns out NGC one is a twin and you can see it looks pretty similar they're really not a huge amount of difference so they look pretty similar you know they've been selected to be the same type of galaxy they're both spiral galaxies they were selected to be that they're actually selected to have the same mass as each other so they weigh the same amount same massive galaxies um they have the same absolute magnitude so the same brightness as each other and they're more or less the same inclination they're not you know one that's not very face on and the other very edge on so they've been selected to be as identical as you can and the only
way reason you can select pairs of galaxies like that is because you've got you know thousands and thousands of them to start with so you really can trawl through and find the ones that are the twins for the ones that you're actually looking for so if I have a copy of the NGC catalog open on my computer there's quite a few different sort of criteria vital statistics for each one not any I mean actually not in the original catalog if we look at so here's the original catalog let me find a page from the original catalog so there isn't actually a whole lot of information right that's NGC one it says what its catalog was in the general catalog it turned out it was one in that catalog as
well and there's a bit of information about what other people have observed it's a bit about where it is on the sky So that's its coordinates it's a bit about how those coordinates might change just due to the procession and so on and then there's a little bit about uh about what it looks like and so I can't remember what the what these stands for I think F Galaxy which means it's faint it's an S Galaxy which means it is small and it's an R Galaxy which means it's round so that was the only information it says it's finding small and round and it's between style 11 and star 14 so that's telling you where to find it on some star chart rather so this was the only information there was in the
original catalog but of course since then people have gone back and observed them and learned a lot more about them so there are kind of expanded versions of this catalog that give us all that extra information about what the mass of the Galaxy is and what type it is and what inclination it's at and all those other things that will match to find these twins so this just sort of provided the starting point for the catalog but there are kind of catalogs that have more information in it so this paper that you have pointed out that has NGC one and it's twin yeah does it actually shed any light on the actual question as to why one's got an active why one's active and one's not it does
in a rather surprising way so this Lambda thing they talk about that's basically about how much the Galaxy so the stars are all moving within the Galaxy and they can be moving in a nice orderly fashion so they're just orbiting All Around in Circles or they could all be moving in random directions okay Lambda gets bigger as things are more rotationally sporty so more kind of orderly motion around and what they found was there's this systematic difference between these galaxies which were chosen to be identical to each other in terms of the way they look but there was a difference in the way that the stars are moving around and in the sense that the ones that were active galaxies tended to have more orderly motion and the ones that
were not active galaxies tend to have slightly more random Motion in them no not me nor them I think reading their paper um so here's the plot which actually shows it so here's this whole bunch of galaxies and so our galaxy was NGC 2906 which is this guy here and then the best twin which is NGC one is up here so this is the difference between the degree of rotational support for the one that's an active Galaxy versus its twin and so if there was no difference in rotation then there'd just be all randomly distributed about zero but you can see they're really systematically shifted upwards and that means that the rotational support for the AGN ones is bigger than the rotational support for their twins it's a slightly controversial result because
the prevailing view of our active nuclei is whether you see a galaxy with an active nucleus or not is pretty much random right that actually it's thought that things just switch on from time to time and then switch off again and so the prevailing view is just whether on you know the number of things that you see is active Galactic nuclei is just to do with this duty cycle of what fraction of the time a galaxy is in this active State versus not and of course if it's just random that you're just seeing the same galaxies and some of them you kept in this active State and some of them you don't then there shouldn't be any differences between the galaxies they shouldn't be rotating differently because that's kind of a
long-term property of the Galaxy and so whether or not something's switched on or Switched Off shouldn't change the overall properties of the Galaxy and so this is a slightly unexpected result that it looks like there is a systematic difference between the galaxies that tend to have these active nuclei in them and the ones that don't and I don't I still think we don't understand exactly you know clearly this is a relatively small sample you know it's what one two three four five six about eight galaxies maybe a larger sample you know maybe they just got unlucky with the statistics it's kind of unlikely because it looked you know it's pretty systematic right it's not like you know a few of them are above and there's a few more above them below they're almost
all above the line here and so it does look like a pretty robust result but it does mean we have to think a little bit more about well why is it some galaxies are active and some aren't and it can't just be this random thing of something switch on and switch off again do you know what I think about if there are If We Ever Meet a civilization that lives in NGC one how they'd feel about the fact that we're in number one on our catalog number one and I wonder what number the Milky Way is in the catalog of other civilizations and it's going to be you know it just come down to John's right because it's to do with how our solar system is oriented and what direction and how the Earth
rotates and all those things that is completely arbitrary you know one Galaxy really is very much like another galaxy so why you pick one to be number one and the other to be 7217 is you know it really does come down just a chance I know why this is invalid but I feel like they should have made Milky Way NGC one just like as an honorary position yeah but that will get really confusing right because there are actually there are NGC objects within the Milky Way because it's got star clusters in as well as galaxies so there are bits of the Milky Way that have NGC numbers when you have an object that takes up a lot of the sky say Andromeda where do you put its uh right and left Ascension is like the
center of the object how do you yeah so you just pick the middle basically all of these the coordinates are kind of defined to be the center of the Galaxy what if it's an irregular object that has no obvious Center most irregular objects are small enough it doesn't matter very much I guess the ones it would matter for are things like the LMC and the SMC but again you get run into this problem because they're actually resolved into individual bits that are actually star clusters within the magellanic clouds that have their own NGC numbers so yeah so but so when you're trying to give a whole galaxy an NGC number it probably doesn't matter that much because it's relatively small on the sky too so with the super
note that with type 1A and type 1B which I won't see I've even heard people talk about active Galactic nuclei as well as like oh this is a type 1.8
