- il y a 2 jours
In this course we will discuss the formation of stars and planets. We will explain the, sometimes violent, processes that occur during their formation and explain how the combination of theory and observation have led to our modern insights. Data from state-of-the-art telescopes will be presented and their impact on our current understanding will be discussed.
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ÉducationTranscription
00:00um let's start the three the third uh lectures of this uh of this module on
00:07star and planet formation by one of my year thank you very much and thank you for being here
00:14despite the rain the weather horrible horrible so um so thank you because i was thinking if i'm
00:22going to talk to an empty room that would also be very nice um so as i promised you i would be
00:30talking about massive stars okay and uh when i was thinking about uh how to to people well how to
00:37to give this lecture i thought why don't i first tell you a little bit about more about massive
00:43stars and why you think they're important and then tell you about all the problems we have
00:48in trying to understand their formation okay and um so i couldn't resist um that's yeah to show you
00:57this round again just to remind you everything about star formation because when you think about
01:05repetition is oh now i know what was happening so there you go i think you can hear me much better
01:12now yeah uh so repetition is always good there is a reason that coca-cola is still a commercial
01:21on television we know all know coca-cola but they still want us to have it to see that that's why
01:28i think it's good to remind you about star formation okay so um we start off with this dark molecular
01:37cloud where there's this equilibrium between the output pressure of the gas and the inward force of
01:43gravity and it's a very delicate balance it just needs a little bit of a perturbation and then the
01:49cloud can collapse and when it's shrinking everything gets hotter and denser and hotter and denser until
01:57the temperatures and the densities are such that hydrogen can be infused into helium releasing a lot
02:03of energy and a star okay and at the same in the process um the cloud is rotating very slowly but it
02:12starts to spin off very quickly and because of that you've got to resolve a centrifugal force that gives you
02:19the disk and since last week unfortunately the recording didn't work but uh last week you may
02:26remember we had because of these magnetic fields we had this pipe on frozen jets so that's what you see
02:33here and at some point all the material that we have from the original cloud is either inside the star in
02:41the disk or has been blown away and we end up with this star in the middle and in the disk the planets are
02:50forming okay there's one big difference already between the low mass stars i was talking about
02:58and the high mass stars that i'm going to talk about now and that's that when they're young the low mass stars
03:04are magnetic which give us the jets but the massive stars are not magnetic because the constitution of
03:13the the star is such that you don't have a magnetic field so things are already different i know this
03:20already before it i could tell you already it's different but there's some other problems that we
03:25have okay um and then yeah what is a massive star i don't know whether you've ever seen a graph like
03:34this perhaps you have this is what we call a Hertzsprung-Russell diagram that's because Hertzsprung
03:42and Russell make the same graph in the same year almost and have essentially named that diagram after
03:49that and what they did they essentially had the color of an object on the horizontal axis
03:59they have blue stars on the left and they have red stars on the right
04:05and as you probably are aware red volt it's a little bit less hot than blue volt
04:13okay because if something is hotter then the the wavelength at which the emission peaks
04:19is shorter you may remember from the first lecture that we have something that was a million degrees because
04:26of the material you could see there's an x-ray so the hotter something is you see the shorter wavelengths
04:34and the cooler something is you see the longer wavelengths also a reason why the stronts always burn
04:42the fingers when they wash their hands because they say that this is cool
04:50um so we've got the hot stars here we've got the cool stars there and what people noticed at some point
04:59they were looking at spectrum of stars and they said oh this looks like the b stars it's a little bit
05:04like children it's like okay this is type a this is type b this is type c and they found that all
05:11the o stars that they called o stars are actually the hotter ones then the b stars and the a stars f g
05:18k and m so that's the horizontal scale and on the vertical scale
05:25we have something and this is something that you can forgot about immediately because
05:31all my students struggle with magnitude so i won't even want to do it to you but
05:36this means that something is faint if i look at it it's faint there's something that's bright
05:43another way of saying is how bright the object is what is the luminosity and here we've got the
05:49luminosity in terms of the solar luminosity and guess what the sun is one solar luminosity
05:57so that's useful and then you can see the scale of how the pressure comes this is 0.01 so that's one percent
06:05so the stars on this line are a hundredth of the brightness of our own star so then this is a
06:12thousandth and this is um but no this is a ten thousandth and this is one two three four five six
06:19a million so something like that so this is really faint and here we've got objects that are
06:25hundreds of times the brightness of our own star ten thousand times and then this will be around a
06:30million right yeah so there's a huge range of temperatures of brightnesses and a fairly large
06:37range of temperatures here we're talking about stars that are about two thousand degrees here we're
06:44talking about stars that are about 13 000 degrees and our own side the sun
06:48is about 6 000 degrees okay and it's long so a little luminosity now when Hertzsprung and Russell
07:02just plotted this they they only knew how bright an object was and they knew what the color was
07:08and normally you would think of perhaps you find stars all over the place but most of the size
07:14actually forms a band in this graph because it's made where we find where we mainly find the stars
07:24we call this a main sequence okay and the sun is also a main sequence star turns out these are stars
07:34that are oops i shouldn't do this with the microphone these stars are at the prime of the life okay join those
07:41and um and we can actually reproduce with our current theories about physics and stellar structure we
07:51can actually explain those now there's some other stars here that these people thought were interesting
07:57to to show and you can see this very big balloon here uh which is a very bright star and it's also very
08:04very big i forgot to tell you discussion indication about how big the stars are so i don't think
08:14it's a lot of goodness mostly um but here we've got red stars that are very big very bright we call
08:22them red super giants and we've got some blue super giants here as well now that's um that that's the
08:32graph i have no idea whether you've ever seen this before but um what you may find this interesting as
08:38well here we've got what i would call massive stars massive stars i would say are about eight to ten times
08:46more massive stars okay um and look at this this object let's look at this one is
08:53probably a thousand times brighter than our own stars so it's burning its hydrogen a thousand times
09:04faster but it's only about ten times more massive so you can see already from a graph like this
09:15that if it's burning its fuel thousand times faster but only has ten times more fuel because it's
09:22setback bigger it will run out of energy a hundred times quicker doesn't make sense that's like like
09:31if you've got a little mini or progeny 106 and i don't know rolls-royce um we find that and this is one
09:39of the reasons that we know that blue stars massive stars don't live variable compared to the last so that's
09:48one one issue that i can immediately say a very massive star will only live for a few million years
09:57and that's nothing for an installment um and things that they do well when they run out and run out of
10:06fuel they can become red super giants which i will show some examples in a moment but um why we really
10:15talk about massive stars is that they can explode and here i've got a picture of galaxy
10:25ngc 1309 and suddenly there was a new light there the nova a new star it was a big one so they called
10:35it supernova and and if i look at it with a different telescope it much better with hubble a couple of
10:42years later this is 2002 2005 you can see there's nothing there right so beforehand there was nothing
10:50then there was this explosion apparently and then there was nothing so light went on and off and why
10:56is this interesting because then you can actually see where there's anything left but we can also look
11:04at the pictures like what was there before can be pinpoint whatever was there that did the explosion
11:12right here's another example yes supernova and there's a picture after the supernova now it's very
11:23difficult to get observations before supernova gets off because it goes off because you never know
11:29but we now know finally 2025 about a couple of dozen of objects and all of them turn out to be a red
11:39super giant apart from both but that's one different story so so we know already that these massive stars
11:47they become these red super giants and they can explode well it's interesting for many reasons
11:53so one of the things is that we think that the universe is expanding accelerating and that's because
12:01of the studies of supernova actually model um and they're very big like the graph that i showed you
12:09um okay compression already but it's too lovely not to show you so um here i've got a panel with uh
12:18with a couple of our own planets earth is the biggest of the four close in but there's nothing
12:24compared to jupiter the jupiter is nothing compared to uh uh to the sun for example and the sun
12:36is nothing compared with what so smaller than serious and serious is nothing compared to these stars
12:42right now this is all the baron i think it's a giant as we call it but all the baron is nothing
12:52compared to battle juice uh battle juice is very small compared to this object called the v y cams
13:01majoris i think it's really lovely to see this how and these things are very big besides right i'll get
13:10back to that in a moment because that is so big and so bright that they can be thousands tens of
13:16thousands perhaps even a million times brighter than our own star there's big implications um then i
13:23want to take one step back and look at the sun um well don't look at the sun but you probably have
13:32to spend a picture of the solid that's nice and yellow it appears but it's not very smooth to look at
13:38when you look at it in detail um the telescope that went online a few years ago and uh we're looking
13:45at the part of the uh i think this is about 30 000 kilometers across and um this is a movie that i
13:55think spends a minute or something like that and you can see i hope that stuff is changing
14:02and what this happens is it's almost like like the sun is bubbling it's if you would have a cattle in
14:12your boiling water you can see these bubbles going up right these are almost like convection cells they
14:19are rising and become a little bit bigger and that happens here as well continuously so let me just
14:26click on play again uh so you can see it's very bubbly it's always like the sun is boiling um um to get
14:37you to get a feeling about how big it all is um that's the next slide uh i hope i don't do anything
14:45wrong uh tibar i might need you okay let's see whether this works yeah
14:55um so what we were looking at this song also looks like an orange mirror this is the bit that we
15:01looked at and if i can zoom in there you can see this is just a bubble that's going off it's a
15:06little bit cooler on the sides and to get a feeling about how big it is not an american telescope
15:13and america thinks that everything is bigger in texas right
15:16but um why am i showing this because in these red super giants exactly the same stuff is happening
15:29it's also bubbly and these bubbles are going going on but um what we now know if you work this out in
15:36the computer you start off with a little bit little cell and it goes up it rises and becomes fair and
15:43bigger and bigger and bigger now i think i just showed you how big these stars are compared to
15:48the sun and i don't have a movie don't worry and i don't have real data but when people put all the
15:54physics that we know in the computer by the way is the stable of life people
16:00so this is a model over a red super giant it's really huge and these convection cells they grow
16:11and grow as they go up and they're much bigger compared to the star than in the case of the sun
16:19let me see where i can get this to work and it's also bubbly this is not minutes this is
16:27so uh but i think it's interesting to to to appreciate that these stars are not like a football
16:37and don't chase it's it's it's active all the time and if i would observe it now it can look
16:45different differently than if i observe it now okay you can see the bright spots move uh all the time
16:52and um i'd love to show you a movie with this resolution but these stars that may be the biggest
17:00stars in the galaxy but they're also far away so they're actually quite small so the best that we
17:06can do uh it's a very recent image actually that um uh was taken and those petal juice uh perhaps you
17:16know the battle juice is in the um constellation of orion um these are his shoulders this is uh belt
17:27this is a sword and these are the feet and um all the stars in blue i get back to that later and this
17:34one is battle juice okay and we've been able to make an image of better juice only recently
17:42uh uh it's roundish good and you've got a very bright white spot here okay so it's still too far
17:50away to show all the details i showed you from the movie but if you would have squinted in the previous
17:56movie you would have found that there would be white spots at some point we can actually uh clear of that
18:03um i believe that we've got some uh we not me but probably uh some other images that it indeed changed
18:12and to put it into perspective again um couldn't resist so this is the star uh this is earth's orbit
18:21uh this is jupiter uh saturn was here so these stars are big okay um okay so
18:33and they also during their life lose a lot of material when i'm looking at these massive stars
18:42then um hardly ever whether you're sitting there well not doing anything most massive stars they use
18:51pretty big amounts material okay and i think a star like this it's i think this one is about 20 solar
19:01miles but in the next 10 000 years it will lose already one or two solar miles so it can in just a few
19:12well in the blink of light in tens of thousands of years these stars can lose a lot of material so
19:17they basically shoot a lot of material but also energy in the interstellar medium right um and that
19:27has its own implications for example i told you about my molecular cloud that there was this balance
19:37between the pressure outwards and gravity inwards well if the gravity image gets a little bit of help
19:44from a wind from the star then gravity comes from the moon for example in these stars materials elements
19:53are being created and they're being shot into space okay so they enrich the interstellar material
20:02with all kinds of new elements so massive stars in that sense are quite important
20:08and indeed um so and i couldn't resist to show you this example this is probably
20:16the most the brightest star that we know of it's about a million times the solar luminosity
20:24and it's called eta car so it is in the constellation of carina and i don't know the greek alphabet but
20:30alpha is mostly the brightest one in a constellation of beta then gamma then delta and at some point you
20:36get out of the car and um but i think i've got the text here so in 1843 it was just a normal star and
20:47suddenly it became really bright and stayed bright for a few years and um what we now know is that we can
20:56find that this material is moving out and i can measure how much it expands and i can work it back and all
21:03that stuff that you see here now we now know was shot into space indeed almost 200 years ago and when
21:12we work out the numbers it looks like perhaps even 20 solar masses of material was shot into space
21:19it's amazing isn't it um this it's called the cauliflower nebula as well probably because it looks like
21:27that one um when you take some other observations we find some you know some material further out
21:36either that was moving a little bit quicker than this stuff or was for a previous episode that it was
21:42moving there and if i zoom out a little bit more and look at x-rays you can see there was even more
21:50material around so these guys these massive stars they're pretty extreme pretty energetic
21:57um they live fast dying or shoot a lot of energy and material and interstellar space now i was
22:05involved in the study of a new object that was discovered and we took some observations of the
22:11object it doesn't matter well it is a different way to make but that's just australian level we found
22:18this is one's ground where we found three shells around but my colleague said why don't you call it the
22:26fried egg nebula because it looks like a fried egg and i said why do you make a breath so then he
22:34actually helped me out and changed the college the color uh uh steam a little bit so so that's the
22:40fried egg nebula i think that was the reason that the bbc once interviewed me for breakfast time
22:46because it's fried eggs are delicious but again that's another example and when i look at
22:53um i'm gonna take a little bit of the distance to the massive stars and i see that they often are
23:01formed in classes they're hardly ever formed alone right and this is a nice picture already but um
23:12you can see this more here's this dusty stuff the dusty material from which i told you
23:17that stars are being formed for example but this hardly any dust there um if i look at i really like
23:25this one if i see here a cluster of these hot blue stars then the space is empty and it looks like it
23:32actually has pushed away the material so they actually do affect their surroundings that these winds
23:41that's that they um that they that they that they eject away just like a snow plow if you got snow
23:49on your driveway wow just find it all um and this looks a little bit familiar so i showed you this
23:59in the first lecture but if i zoom out i've got exactly the same here here it is the pillars of creation
24:07um you've got the same idea you've got a little bit of a cluster here where gas is being pushed away
24:14and it's surrounded by all this dust and you may remember that i told you that the densities here were
24:21a little bit of stromanoff um stromanoff for uh stars to form okay then um this is probably even a better
24:31picture this is a cluster in a small measuring cloud very far away you've got the blue stars you've got
24:38the material that's being cleared out this is your optical um but if i look here it looks like it's a
24:45little bit denser here there i have in infrared a lot of dense material that might be actually forming
24:55stars because you may remember that young stars are being recognized as x-rays okay and that's what
25:03we see here this is an image of the same same um region in x-rays here i've got uh x-ray source stars
25:12being formed associated with the dust uh that is being heated by the stars and this is a composite
25:20um um i what i really like to point you out is you always felt one of these these awful galaxies that
25:27make our life so difficult right people stay basically very interested in the stars the people
25:33who are interested in galaxies they don't like the stars that are in the foreground and we've got the
25:37galaxies but it looks like that that these winds that are emanating from these massive stars might
25:47actually induce trigger star formation this is the blue that uh i need you tibon um and um we call
25:58this trigger star formations so here i've got myself a cloud this is um this is not even computer
26:05model this is just uh just this is an artist who actually uh thought i can do this um here we've
26:13got the cloud and here i've got a star and in this case i let the star explode let's see what happens
26:19so if you look so this star bang shockwave it gives the molecular cloud a kick and before you know it
26:28first basically condensed collapsed and starts will create so that's the concept of triggered or induced
26:39star formation so one of the reasons why we say that the molecular stars will actually collapse
26:44is basically because gravity gives some help from an outside source thank you so we'll go back
26:52since this
26:55yeah can we ask questions the dog yes of course um it says that this message that's getting too far away
27:03yeah any reason is it going to oh oh i'm i'm making very first a i generated image
27:11to actually explain this so quickly you can hear this thank you um so my question was the um um why
27:20these massive stars are probably from this yeah and i respond it's like i'll tell you in two minutes
27:26so um um colleague of mine in the uk basically computed something like this
27:37in the larger scale and what he did he put some very massive stars in the center of a cloud
27:44and he put a couple of stars here this is gas that is just floating around in between stars
27:57and some parts are a little bit less and just to again demonstrate to you the effect
28:05that massive stars have on the surroundings he made this movie and he had a couple of stars in
28:12the middle and at some point they will explode because these stars these massive stars
28:19they only live for a few million years so this movie runs for a few million years so i'm going
28:25away for coffee and uh can i click so bang that was the first one you can see there's a lot of
28:32material being shot out and uh material here is being disrupted but i think what you can see is
28:38already there's a little bit of a bubble being blown already by the shortwave just like we just saw
28:43with these clusters right and um so that was the most massive one that exploded the system is now
28:49three million years old uh all the gas here thinks that it's okay uh mining its own fish so there's
28:56another one going off uh and another one and another one and at some point this bubble gets bigger
29:02and everything that we were looking at gets disrupted so i think he only put in three or four
29:10of these massive stars close to each other which is not really a rare occurrence and you can see it
29:16can have a big effect on the surroundings and that can also explain when i'm looking at galaxies like
29:24these that in the center this is what we call the starburst galaxy where a lot of stars are being
29:32formed uh thanks to all the supernova that went off which is actually being shot out of this galaxy okay
29:41uh so so that's the bottom line really at master standard actually quite yeah influential that's
29:49probably a nice 2020s work um and um even even better he would not be there without massive stars because
30:03after the big bang we only have hydrogen 70 percent of the material and some helium and typically almost
30:15every other element that we know is made in stars as i mentioned already stars born when hydrogen is
30:23fusing into helium the next step would be will be that helium fuses into carbon and so on and we found
30:34quite a few different ways uh of how elements are being formed when you look at a symbol like this
30:42that's what we get in low mass stars like the salt so the carbon and the nitrogen so the carbon that
30:51we are made of the nitrogen that's in the air most of it that we encounter in the galaxy space is made in
31:00in low mass stars but oxygen for example most of the oxygen that we see is coming from these massive stars
31:08stars because more massive stars they can actually create much more elements than normal stars um there's
31:15another one thing that um uh i'd like to highlight this is actually a quite a new uh discovery you may
31:24have heard of gravitational waves but massive stars that explode explode can leave a black hole but you can
31:33also leave a neutron star and it's very rare but sometimes two neutron stars would be in the system and at
31:41some point it could even words come together and it would give flesh a space-time fabric to give some waves
31:48gravitational waves nowadays we can actually measure that and what we also now found is that during
31:56these verges of neutron stars other elements are being formed uh for example gold all the gold most of
32:04the gold that we that we see might actually be the result of a virgin neutron star okay but why i'm but
32:13i'm showing this really is without the massive stars we would not have the oxygen yeah without the massive
32:19stars we also would not have the cold for example so that's why we astronomers are interested in
32:26the massive stars okay we can see them but one of the big questions is how do they form
32:42and we have all of those elements on earth yeah yeah uh we just have one zone yeah um will they all come from them
32:52uh we are second hands so um imagine that um the the soul the the sun is only five billion years old only and yes
33:07as we know it's about four and a half billion years old but the universe that they bank was 13 billion years ago
33:15so it's a long time that uh that uh uh passed by between us so the first stars were only made of
33:25hydrogen but then they made similar elements explode then that material was the interstellar media new
33:35stars were made formed second generation etc etc so what we the sun is made of because there's also iron in the
33:44the sun there's zinc there's gold in the sun not a lot but that's not made by the sun but it's from the
33:49mixed material from all these dusty clouds that people started yeah um and we're now at the stage that we
33:58think we look at the very all the stars and they seem to behave differently depending on where you look so
34:07supernova one went off made a little bit more iron and nitrogen and supernova over there went off less
34:14iron and these stars you can see that now mostly it's a mix
34:22eight billion years as well um and
34:25and we have we have very very very big global forming these stars and um i didn't tell you yet but
34:39what why these stars lose material um i i turns out these stars are so incredibly bright
34:50that they can actually blow away their outer parts
34:56how can it happen now um i've been talking about pressure all the time right and um the air
35:04the air molecules here they move about and they bounce off the wall of the whiteboard
35:13also knocking against the wall basically gives such a pressure if i would have a hot air balloon
35:19and i would make the air hotter actually what happens is that these air molecules move faster
35:27uh imagine now with just two molecules one here and one down there and this one
35:38now it turns out that you don't need molecules for atoms to do that but photos the light can do that
35:46so if i just have a tiny molecule here and a very very very energetic photon it could actually impart
35:57pressure on radiation pressure okay um um um yeah so this is the second image i have amazing
36:07a high and i don't know what i'm proud of what i said make an image for its radiation pressure but the bottom
36:14line is that photons can exert pressure and in this case it's the same in both but people are actually
36:22in our own case in the song are thinking about how can we actually power uh uh satellites and this is
36:30serious stuff people are actually thinking about solar sails that actually power and accelerate into
36:37planetary crops so photons can do the job they can push away material and you can well imagine that if
36:45you've got a star that's 10 000 times or a million times brighter than our own star of sun that's a lot of
36:52focus and these stars are also very big so the gravity on the surface is not that strong right the further
37:02away you are it's a little bit less so it turns out that if i'm looking at massive stars they can push away
37:08the outer parts these are the widths and they can be as i said right extreme the same problem
37:17actually occurs in the formation of the stars remember that it's not only the cloud that's collapsing
37:24but there's also material falling onto the star if you do the calculations and you let material fall in
37:32then the moment the star is about 10 15 solar masses it is already so bright it stops material from
37:41falling onto it so that was that is a problem for a long time it's it's fairly basic computation to make
37:55how bright is the star need to be for it to stop material falling in
38:02i think this was identified in the in the 80s and people have been thinking for a long time like
38:11how can we do this and that the very popular theory was at some point ah that if i've got two stars
38:19they merge and your story i've got a bigger one but in order to explain every single star that we
38:28message started looking at in the world um and then people thought differently and i'm not trying to
38:39show you this movie again because this was actually done for massive stars and let me just run you
38:45through the simulation again uh so you remember this is the cloud and this top view there's a side view
38:54and there's a zoom in so the moment i switch on the physics you find that basically a disk is being formed
39:01so let me just do that again if i just click uh uh uh i think i should i just try yeah here just play
39:18so um so you can see already it's moving very quickly uh this is spreading out and here sweat and here
39:28there's actually this bipolar flow that has nothing to do with the jets from last week but that's
39:35already pushed out by radiation pressure okay but the saving grace in this entire story and it's
39:44amazing when you think about it because people had to fight about it for a long time but yeah if i have
39:51a disk of material that is very difficult to push away all the computations that people did they said
40:01okay i have material that is talking this direction from this direction this direction this this this
40:06this direction and the radiation is also going in exactly all these directions and they worked out it
40:12was not a link but if i only can see that this disk is not capturing a lot of photos from the start because
40:23most of the problems are going out it turns out that if you have a disk of material and that falls onto
40:31the star then we can grow them bigger so that was the theory are you with me okay so the disk will help
40:40you i should have taken my my frisbee with me again but um the disk captures only one percent of all the
40:46life from the star well the the theories that they had before and they thought you needed all the life
40:53so in a way that's some of the theory that people have is oh perhaps lesser stars form like global stars
41:02it's still a little differently but they form from the collapse of the cloud and i got this disk so far
41:07so and then what you want to do that's what we offer some insights we observe something we do an
41:17experiment and then we have theory to try to explain and the theory can make predictions and then check
41:25them with observations and that's basically how we make progress improve the observations improve the
41:32theory and um yeah if the theory because the theory is just a computer code or an invasion of this paper
41:42um the the the the challenge then is to see whether there are indeed disks around massive star
41:51then we run into some other problems and here's the answer for your question my first um
41:58um i generated image um i don't think i told you but you might not be surprised that if i go to the beach
42:10then there's uh a lot of small dust grains and sand grains a few panels and a few blocks so there's
42:17always more small things than big things okay if i look at stars i have many more small things than big
42:26things i yeah now let's think about the very first this hurts from russell diagram i had a lot of red stars
42:33here i know you've seen blue stars there but you remember so the bottom line of such massive stars are rare
42:41there okay okay and if that's the case then on average they will be further away from you and that's
42:50why i thought okay i make this this this uh as an illustration if i'm at any position on the screen
42:59i'm almost right close towards black dot right but i don't have i only have one black dot
43:05black dot so wherever i am on the screen with a few exceptions my red dot will always be much further
43:13away from me than a black dot so that's a problem if you want to observe disks because if something is
43:25further away that will be smaller than the sky and if it's smaller than the sky i need a very good task
43:33so that's one of the main reasons already that we know so much less from massive stars than for loma
43:44stars because on the first lecture i showed you all kinds of nice images of this we would not be able
43:51to make them for the massive stars so yeah um so we need a very high spatial resolution i see people
44:01already leaving so what what time should i stop because yeah are we okay yeah okay so we need very high
44:11spatial resolution the other thing is that you have to concealment of all people because and then i want to
44:22go to all right again we just look at battle choose but you see a lot of blue stars so that is already a
44:30region where the region where stars are quite young and massive but it just has nothing to do with
44:35them these guys are related um i grabbed this picture of the left someone actually must be a very good
44:43average astronomer because he made such a long exposure that he got this so you can see he's still all
44:50right but there's a lot of natural to think about the gas that this says is heated water by stars it's
44:59already a bit of a signpost of star formation so there's a lot of star formation going on but what
45:06we don't find is that most of the star formation is actually obscured from view by these molecular clouds
45:16one of the reasons is that's massive stars they live much quicker than the entire cloud but the problem
45:23now is that if i can study the youngest massive stars in optical wavelengths i need to go to longer
45:32wavelengths just like you may remember that the longer the wavelength you can clear through the dust
45:38so i need to not only have a very good telescope with very good spatial resolution
45:44but i also have to walk away from the idea that i can look at that with my own eyes that optical light
45:51i need to do something for problems um and it's only in the last decade two decades or so that we can do
46:00that um and um as an aside this is where i'm not getting into trouble to try it with
46:07um it's not only difficult to study them but it's also difficult to find them because if they're
46:15invisible then you don't know where they are and i think a nice examples here i'm looking at the galaxy
46:21not our galaxy uh lives on m51 and optical light and you may recognize the dusty patches
46:30we now recognize this reddish glow that i just showed you as well um and here i'm looking at it
46:38at infrared wavelengths where the dust on the molecular clouds is formed by the stars and here
46:45i can keep going further here it's actually quite easy to identify the regions the stars form
46:55we don't look at our own galaxy levels we're in the middle
47:00uh anything where i would expect massive stars to form is hidden from view
47:08uh it's only since recently that we actually have been probing the galaxy that could enough
47:14resolution many wavelengths to pinpoint regions where it could be then we need to follow them up and
47:21then say oh yeah that's massive started um and here uh we we see the the inner part
47:28that's probably this um optical uh light that infrared light further infrared and even a millimeter
47:39so it's basically observations like these that we finally can say oh there's an object that's worth
47:45your study so then you finally have a separate stars that you can study they need a big telescope and here
47:53here is a nice picture of the european southern observatory that's chile where they've got four
48:02telescopes they're all called vlt very large telescope and they're eight meters across but what we can do now
48:15is actually combine the light of the individual telescopes to mimic the big telescope
48:24and i think the biggest distance here is about 100 meters so we can mimic a telescope that's about 100 meters
48:32so it's a little bit more complicated than that of course but the resolution we can get
48:42is what we call three milli arc seconds one degree has 65 minutes each arc minute is 60 arc seconds one arc
48:52second has thousand milli arc seconds uh but uh if i would be uh uh look at an astronaut on the moon
49:01you would be about three milli arc seconds so a question idea how small is it the only problem is
49:08that you can only mimic that big telescope in one direction okay so if something is oriented in this
49:17direction of the sky you can say whether it's small or not but not like this so if i find my bottle of
49:22water if my telescopes cross it in this way it can say well it's this point and i've got a set of
49:29telescopes that's looking in this direction it can say it's this at this point but that's the limitation
49:35that you have okay so it's really basic stuff that we can get from it but um 15 years ago
49:44colleague and now in britain he actually found one of these nysos these massive young stars did a lot of
49:53observations and this is what he got world famous and it's a very ugly picture and that's the thing
50:03we always pushed our telescopes to the limit and the result is not very pretty but uh this revolutionized
50:11uh story really because the object that we were looking at he was looking at is actually elongated in
50:18this direction essentially like this this is how the smallest thing that you can see okay and um um
50:28this was the first time that we actually had evidence for a very small disk around a young messenger
50:36star so it's only one but here's the problem that's 2010 and still the best example that we have
50:44uh um i skipped the next thing because i want to go through another telescope
50:52um there's another big telescope called alma it's called the atagama large millimeter array
51:01and it's a red an array of telescopes that is looking at large millimeters
51:05that's a joke that's a joke but i showed this to a theoretician and said their name it's the
51:14large millimeter and i was stumped for about but it's a large array okay and it's probic millimeter
51:22wavelengths and it's located at five kilometers somewhere in the andes and this is one of the examples
51:31that belgium cannot pay for it europe cannot pay for it the americans cannot pay for it the japanese
51:39cannot pay for it together this is a joint absolutely worldwide collaboration where we're looking at
51:49the sky at millimeter wavelengths
51:51uh that's very sensitive cold stuff wavelengths are very good long and it's also sensitive to
52:00molecules because these are the same ways that war the water in your microwave
52:07but the water molecules they really like the energy they get from them that's like like like
52:13like a red gold ring so for what you get some some millimeters of an edge and that's why this is also
52:21five kilometers high because all the water vapor in the earth atmosphere which absorb all the
52:27the millimeter life from outside so this is another few three-linear desert um and across cool of the
52:36molecules i'll show you the best example we now have for a disc around the massive star
52:47in different molecules so i i have no idea what molecules they are it could be cyanide for all i know
52:56but um you may remember that i told you that if something is red it's red shifted it's moving away from
53:03this and if it's blue shifted it's moving towards us so so these are not only disky structures from the
53:11way you look at them but you know they're also rotating okay so the number of objects that we have
53:18is still very human but at least we stand to think now that um we can form massive stars so yes all the
53:29life from these massive stars now pushing away material but if you can circumvent that problem
53:34by having a disc around the object that's the theory but from the observations we're now getting there
53:41as well still a long way away from from from uh having all the questions all the answers because
53:48um we're getting there so yeah this is the theory some some some broad pictures of these massive stars
53:56and the very last thing that's my last minute and if you don't mind now we think we got it sorted
54:02that we know how to form a single star and there's a revolution going on in the stormy as we speak
54:11we find that everything that i've been telling you that i've been telling my students that
54:18thibault meller has been telling his students is a lie that's wrong it's not a lie because we found in
54:26the last decade or so that 100 all the massive stars i'm talking about are not alone they're in multiple
54:37systems so perhaps two stars orbiting each other three stars orbiting each other and that complicates
54:44things massively because everything that we've done everything that we thought is about one star
54:51doing its business losing its mass for example but and this graph shows you the mass of stars or if
55:01you like the spectral types and this has the multiplicity fraction this is 100 all the massive o and b
55:09stars are in these binary or multiple systems and if i'm looking at the lowest largest objects
55:17when we study these most massive objects some of them are very close to each other some of them are far
55:23away from each other and if i don't look at this only 30 percent of all the massive stars that i've been
55:31talking about they're got there might be in binary but they're effectively seen so far away from each other
55:36nothing going on but 24 of all these massive stars i've been telling you about they are so close to
55:45each other that at some point in time they could actually touch each other and merge
55:52that's quite something a lot of stuff is happening and in the other situations they might be stealing
56:00materials from each other they might be disrupting each other they might be making this is the
56:05revolution that's going on life is much more complicated but it's always the case right and
56:13the biggest problem at the moment with the young stars is that we find these binaries when they're
56:19very young it's never close enough for them to merge if i'm looking at all these main sequence stars
56:26so the prime of the line 25 are so close that will merge if i'm looking at all these young stars none of
56:35them are close to each other
56:39and that's the second right to that so we still have a problem but then again that's always the case
56:46you answer the wrong question you get 10 different projects so uh questions so um next week
56:52i talked about planets mission for the moment thank you very much
57:06any questions
57:07it's sharing the quotes uh you cannot be a massive star alone basically you cannot just seem absolutely
57:29exactly what we find yeah but we don't know yet why we have seen it now but we can't explain it yet
57:40so that's the next challenge absolutely
57:43thank you
57:54no more questions so i know you can see you offering micro certification please register
57:59please uh and uh thank you very much for me again because it's a very nice talk thank you
58:05and it's starting sort of the end of the day so if you start the day you need to fill up with the right
58:10have no religion for that issue
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