 This is one of the triest places on Earth. Sometimes it feels like being on a moon or a mass. During the day is a fantastic place, but during the night is absolutely astonishing. Hi everybody, welcome back to the journey through the extreme universe. Today we are here to celebrate the dark matter day, which actually is happening on Sunday, but we couldn't wait to talk about this mysterious component of the universe. So in this webinar, we are going to learn what we know so far about dark matter and something that we don't know is its nature. A way to disentangle this mystery is upsetting gamma rays. So we are going to learn also, thanks to our speakers, how CTA is going to try to unravel the nature of dark matter. And as I said, we have today speakers. In plural, we don't have just one mission commander. Today we have with us three mission commanders that I'm going to introduce in just one minute. But as usual, I always give you this reminder. If you have any comments, questions, if you want to say hi to us, you can do it already in the comments on Facebook and YouTube. At the end, we always have this question and answer session. So if you have a question about dark matter and you never knew who should ask, this is your moment. Don't be shy. Send your question to the speakers. We'll answer it at the end. So with that, let me introduce, let me welcome the speakers. We have today here Javier, Mabel, and Judith. Hi, guys. How are you? Hi, everybody. Hi. So first of all, thank you for joining us today in this special webinar, actually, because it's the first time, as I said, that we have several people, several speakers. Today, Javier is going to give these historical, scientific contexts on dark matter. Then Mabel will talk about the dark matter sources we have in our own galaxy. And then Judith will talk about the dark matter sources that are far away in the extragalactic universe. Actually, the universe we discussed in the previous webinar. Before starting, I would like to introduce you to the audience. I'm going to do it in order. Let's start with Javier. Javier is an astrophysicist. He's working at the Institute for Theoretical Physics in Madrid, who actually recently defended successfully his PhD on searches for dark matters of halos with gamma rays using the satellite thermal lab and the observatory CTO. Then we have Mabel. She's also a doctor in astrophysics, currently working as a postdoc at the University of Padua, here in Italy. Her work has been centered in the development of software for the analysis of the data from the CTO's large-sized telescope. And she also worked in the studies of prospects for the detection of dark matter with CTO. And finally, we have Judith. She's a PhD in her final, in her last year, also at the Institute for Theoretical Physics in Madrid. And most of her time has been devoted to model the dark matter content with CTO, mostly for these extragalactic objects she will talk about. So again, thanks for joining us. And let's start today with Javier. Javier, whenever you want. Thank you very much, Alba. And thanks to the audience for being here in this very exciting webinar. So today, we're going to talk a bit about dark matter and how can CTA say something, maybe, about this mysterious component. So the first thing to talk about here is the evidence we have for dark matter. We don't know, actually, what dark matter is. It's ultimate nature. But we have a lot of evidence of its existence. Actually, this is a long-standing mystery in modern physics because we have evidence since the early 1930s. So we are approaching dangerously its centenary. So yeah, it's a very long-standing mystery here. And we have evidence for an invisible matter component in the universe that it's five times more abundant than ordinary matter. We understand by ordinary matter everything we know, basically. And some of these evidence can be found in the galactic rotation curves, the galaxy cluster dynamics, and, very famously, the cosmic microwave background anisotrophic, which is the rightmost graphic here. You will, for sure, know. So now we have the evidence. It's interesting to talk about what do we know, actually, about dark matter in this next slide. And what we know about dark matter is these three things. We know a lot of things, but mainly this mysterious component is electrically neutral. And this means that it doesn't emit or reflect light. So it's very difficult to detect. We cannot just look at it in principle. It's extremely weakly interacting at most. Maybe it's not interacting at all with ordinary matter. This is also a problem because we know ordinary matter. We don't know dark matter. And, finally, it's collisionless. This means that dark matter is almost unperturbed. It's very difficult to see its effect on itself. So this makes its detection very, very difficult because, main points, it is invisible and it only interacts gravitationally with its surroundings. It is very useful to obtain evidence of its existence but doesn't tell us anything or practically anything about its ultimate nature. Now, in these last, say, 100 years, more or less, physicists have been very, very, very busy developing models for dark matter. We don't know what it is, but we have a lot of nice ideas. In this graphic here in this plot, we can see some of the just most popular models for dark matter. I don't know the number. It's, I don't know, 100, 1000, whatever you want, models for dark matter. And we are a bit lost, actually, because they expand more than 60 orders of magnitude in mass. Just to have a taste of what does this mean, we have particles in these models, as light as actions, which have masses of a billion of the electron, so extremely, extremely light, up to very microscopic candidates, such as primordial black holes, which cannot be considered just an elementary particle, but a macroscopic object. And they can be as heavy as hundreds of time the mass of the sun. So we are talking here about extremely heavy objects. So we have a huge range from the billions of the mass of the electron to hundreds of time the mass of the sun. And everything is permitted in principle. Dark matter, it's very flexible in this sense. So you may ask now, okay, why are we talking about dark matter if it's invisible? If we cannot see it, actually, with a telescope? Well, fortunately, there are some models, some very, very interesting models, in which dark matter can interact very weakly. Remember, I said at most, it can interact very, very weakly with ordinary matter. But this interaction is enough for our purposes. Why? Because in these interactions, as you can see in this plot at the right-hand side, you have two dark matter particles. Okay, these blue balls. And they interact, they collide, producing in this process a standard model of particles. So ordinary matter, particles we all know and love, such as quarks, bosons, etc. And as a by-product, as a bonus, you get a lot of particles from these ones. Namely, you get, as you can see, there are positrons, electrons, neutrinos, etc. And also photons. Photons are light, of course. And you have low and medium gamma ray photons. They can also be high-energy gamma ray photons. So if we are dealing with gamma rays, we have CTAO. So we have the best instrument possible to take a look. Now, how do we take a look at this dark matter annihilation? Let's say this dark matter processes which produce actually this gamma ray. Well, each gamma ray source, each astrophysical source, actually, regardless of the wavelength, is characterized by its spectrum. The spectrum, just to have a taste, is like a unique fingerprint for each source. Okay, we have our fingerprints, and they tell us, I am Javier, you are whoever you are. Okay, by your fingerprint, a source is exactly the same. Each source has its unique spectrum, its unique fingerprint. As you can see in this plot here on the right-hand side, a typical gamma ray source is a straight line. Okay, this red line here. And the other lines you can see that are very curved, the blue one, green one, black one, of course, are dark matter annihilation spectrum. So dark matter annihilating into gamma rays. And they produce this very, very curved spectra that, as you can see by eye, they don't resemble any bit the typical gamma ray source, which is, by the way, active galactic nuclear IGN. If you take a look at the other webinars, you will see this term a lot. So it's very interesting because here, nature is telling us you can actually distinguish between a well-known gamma ray source, a typical gamma ray source, and dark matter annihilation. They are very, very different. And you can see now in the next slide, by changing the interaction type and the mass of the particle, this spectrum changes a lot in the bottom part of this plot. You can see something that puts M equal to 10 GeV, M equal to 100 GeV. This is just barring the mass of the dark matter particle. I told you that the mass is a huge, they have a huge possibility in this particular model. Of course, the freedom is reduced a little bit, but you can have, of course, some freedom for the mass. And as you can, you barrow the mass, the spectrum, the fingerprint, also bar rise. So this is very interesting because, depending on the fingerprint spectrum, you detect with CTAO, you can see something about the specific nature of dark matter. You can say, I know that dark matter is this model with this mass. So you can obtain a lot of information. This is absolutely brilliant. And now in the next slide, you can also see that here, we are just changing the interaction type. We have a lot of interactions. If you change the interaction type, you see that the numbers are the same, 10 GeV, 100 GeV, et cetera. But the spectrum, the shape change a little bit. So again, depending on the shape and where does it, where do we found actually this spectrum, we can say, this is dark matter. This is the interaction type of the dark matter. And this is the mass of the dark matter particle. So everything basically. And this is marvelous. This is brilliant. So we have basically everything. We know that dark matter exists. We know some models for it. And we know that in some models, we can have gamma rays and how to distinguish them from a typical dark matter, a gamma ray source. So the question is now, where do we look for dark matter? The thing is that a gamma ray signal in dark matter annihilation is proportional to the square density of dark matter. So the density we have, we need more precisely a very concentrated object, very dark matter dominated systems. And as we want to maximize the gamma ray flux, of course, we need them to be as close as possible. So in this sense, we have galactic and extra-galactic targets, targets in our own galaxy and targets far away from our galaxy. So this is the gamma ray sky, seen by the Fermilat satellite in eight years of operations. Okay. You can see, as you may see in other webinars, the prominent central feature there, the red and yellow band, is our own galaxy. And then you have a lot of sources in the sky, a lot of different things floating around. Now, we can ask ourselves, okay, this is the actual gamma ray sky we are seeing, but if we have only gamma dark matter, how would the sky look? So the answer is here in the next slide. This is a simulation, of course. We don't know if we have detected dark matter yet. And you can see that the picture is very different from what we saw in the previous slide, because now we have a spherical feature there, which is the galactic center, and we will hear about it in one minute. And then we have a lot of point sources around, but we don't have this feature of our own galaxy. So it's very different. By comparing these two maps, we can actually say a lot of things about dark matter and hopefully find it. And now, specifically, we can distinguish between many targets. We have the galactic center, the Milky Way halo, nearby galaxies, et cetera, et cetera, et cetera. So many different targets. I will stop here now, and I will leave my colleague, Mabel, to speak about the galactic center and our interesting galactic targets. Thank you, Javier. Yes, so the first source that we can think about when we try to search for dark matter is very close by to us, and it's probably the galactic center, meaning the center of our own galaxy. And this place, the galactic center, actually it's the place where we can expect the largest dark matter signal in case of that we can detect it. So this region happens also to be a very active region full of all kinds of types of sources. And of course, a lot of gamma ray sources, a lot of diffuse gamma ray emission. And so for this reason, the galactic center is one of the most important targets for CTAOs to be observed. So for this reason, CTA is preparing a survey of this region that we can see in the next slide, the distribution of this survey, meaning that because this region is extended, CTA will perform a series of different observations to cover all the area. And it will dedicate more than 500 hours of observations of this place, meaning that we will have plenty of data, plenty of observation time from this region to try to search for dark matter. Another very interesting source that it's really close by, it's not exactly in our galaxy, but it's really, really close will be the Large Magellanic Cloud. The Large Magellanic Clouds are satellites galaxies from the Milky Way. They can be seen from the southern end spheres, and they are one of the closest galaxies in our local group. They are located at about 50 kiloparsecs, and they are seen as extended objects from the Earth. So these galaxies, which are irregular galaxies, they have a lot of activity in a star formation, which means that they also have a lot of gamma ray sources, like supernova rendments, like pulsar wind navel air, like binaries, and stuff like that. But also happens that we know that they have a huge content of dark matter, like a remarkably huge content. And we know that thanks to studies on their rotational curves. So because they are very interesting objects, they allow us to study galactic physics outside our galaxies. It's also one of the most important goals for CTAO. So CTAO will perform also a survey of this region. And we can see in the next slide like a distribution of this survey, like a preliminary distribution, it will dedicate more than 300 hours of observations to cover all this extended area. And of course, again, we will collect a lot of data to do our searches for dark matter. Other nearby sources that we can also study and that are really also close by in our local group will be the galaxies Andromeda M31 and Triangulum M33, which happens to be also very interesting because they are spiral galaxies. Meaning they are the same kind of galaxy as our own, as the Milky Way. And even if they are a little bit more far away than the Magellanic Clouds, they are also close enough to be observed as extended objects. So this allow us also to take advantage of the distribution of the dark matter emission to really try to disentangle the dark matter signal in case there is. Okay, so how do we search for dark matter in this kind of object? So the problem or the challenge that they present is that, as I said, they have huge activity in, let's say, in ordinary astrophysics. They are full of astrophysical sources such as supernova rendments, they have binaries, they have pulsar veneville, they have diffuse emission coming from cosmic rays interacting with the interstellar medium. So how do we distinguish the emission of all these sources from the one that comes from the dark matter? As Javier said, dark matter has its own spectrum, it has its own shape, but when we have a very complicated source, a very complicated target, this is not that easy. We have to know very well how the astrophysics of the sources that are present in the target works. And how do we do that? The first thing that we need, as we can see in the next slide, is to build an emission model, an emission model of the gamma ray emission from these sources, meaning the gamma rays from the ordinary astrophysical emission. So for example, in the galactic center, which we can see in the image on the left, these are examples of the different components of the gamma ray emission coming from the galactic center. We can see that there is an extended emission from cosmic rays. There are a lot of small, different gamma ray sources we got seen as puntual sources. There are different kinds of extended emission from cosmic rays interacting from the interstellar medium. So what we need is to put together all these components to predict the gamma ray emission that we expect from this direction of the sky, from this target. And then in the case that we can detect any extra signal that cannot be fit with any of these sources, we can then ask us, is this coming from dark matter? So as we see in the next slide, what we can do then with this extra signal that in the case that we detect an extra signal, of course, we can try to see if any of the many models of dark matter that exist or that we can afford to test, meaning those models that predict that dark matter will produce gamma rays through annihilation, we can try to see if this emission fits to any of these models. So we can say, okay, this emission is compatible with this kind of dark matter model or maybe it's not, right? Maybe it's not compatible with any of the models that we have. So we can say, okay, then the nature of dark matter is not in this direction. So what we can do is to try different annihilation channels. We can try different density profiles, meaning how the dark matter mass is distributed in the target. We can try different dark matter masses, etc. Okay, what happened now? We don't have data yet, right? We have to wait for CTAO to be built and to be working and to take all these hours of data to be able to perform these fits to our emission models. But still, there is a lot of work to do in the meanwhile, right? The first thing will be, of course, to prepare realistic emission models to compare our data with. To do that, we have to understand very well the cosmic reistrophysics of our sources, our camera reistrophysics. So we can work that in meanwhile. We can build our emission models and also what we can do is to perform predictions. We can make simulations of the emission of these targets and how CTAO will observe them and how CTAO will behave observing these objects. So we can see how sensitive CTAO will be to these kind of targets and also which dark matter models will be reachable by CTAO because some of them will not emit enough light for CTAO to detect them or there will be. So we can have an idea of what can we try to search in the data that we will receive. So regarding these prospects and these predictions, what we do is to build sensitivity curves that we can see here in the next slide. This sensitivity curve tells us a hint on the set of different models that CTAO will be able to test, to reach. In these curves what we see is that for different dark matter models, for a different dark matter profile, a different dark matter annihilation channel, a different dark matter mass and the annihilation cross-section, what set of parameters will be reachable by CTAO. For example, in the left you can see different models when CTAO is observing to the galactic center. This is all done with simulations. But these curves mean that all the models that are above these curves are models that somehow CTAO will be able or to detect or to discard in the case that CTAO doesn't detect anything compatible with dark matter. Looking in that direction then we can say okay dark matter it's not in this region. And especially we are very interested in this blue line that you can see in the left plot and it's a dotted red line in the right. This is the thermal cross-section. This cross-section basically defines the set of models inside this weak interactive massive particle theory of dark matter. The set of models that actually would allow to recover the distribution, the density of dark matter that we observed today. So we are very, very interested in CTAO to be able to prove the models that are in this area. And as you can see the galactic center is very promising because a lot of models, a lot of sensitivity curves are below this area. In the large magnetic cloud which is the curves in the right as you see it's more complicated because the large magnetic clouds are farther away. They are complicated objects with a lot of sources and this can difficult our task. So as a summary of this part these close by dark matter targets are very interesting because they have high content of dark matter and because they are very close to us we can expect strong dark matter annihilation signals. The problem is that they also have strong backgrounds strong gamma ray backgrounds from other gamma ray sources that are present there. So what we have to do it's to perform big efforts together with the galactic and cosmic ray science groups inside CTAO and also in collaboration with other experiments with our institutes in order to be able to understand these backgrounds to build proper and very realistic emission models which allow us to really study the dark matter. And now my colleague you did will tell you more about other sources other targets for dark matter farther away. Yes, so Mabel has already told us about some targets that are indeed non-galactic like for example these nearby galaxies but now we are going to talk about other interesting extra galactic sources of gamma ray from dark matter origin which can be in galaxy glasses and also in galaxies for example. So first of all we are going to talk about dark further galaxies indeed Mabel has already introduced them and okay as its name says dark further galaxies are really small galaxies which usually are companion galaxies to other big galaxies class for example in our neighborhood we can find satellite the dark further galaxies which are accompanying like the new well and M31 but however they were discovered until 1938 so how can it be? So according to structure formation history of the universe these dark further galaxies are the first one to be formed so after all these formation history processes these very small galaxies and being cannibalized but the bigger galaxies so the remaining ones are still not a lot of them and they host like a very old population of start which appear to be very faint and also they do not host any kind of hot dust or hot gas so they really appear to be very faint in the sky however from the information that we will get from the future telescopes and the future observation it is expected to be discovering more of these kind of objects another interesting thing from them is that their stars that they host are not in rotation so we cannot provide rotation course from most of these objects and the way we have to measure the mass and their properties is to try to measure these random motions the stars that they host the go through in them so we call that the stars to their galaxies are pressure supported systems and talking about the mass just these objects are of the order of a million times in the lightest of the case the mass of half the mass of the sun and aside from being an astragalactic voltage they are the nearest to us being always less than 1.5 million light years from us however because they are really small they appear as a point sources in the sky okay so having this mind being this small and to this distance in order to account for the mass of these galaxies we need a thousand times more than matter than standard matter meaning that we have one of these best conditions that Javier was mentioning before of having a very strong dominated dark matter objects taking this into account we have more than enough in order to point austere telescopes to large star galaxies but the other thing that it's very good from these objects in contrast to what we have seen from galactic objects is that we do not expect any other kind of gamma ray emission from this object that it's not coming from dark matter so it will be really a smoking on to detect any kind of dark matter emission from a dwarf ferroidal galaxy as Nadel has told us here we have some prospects on sensitivity curves of the planets observation of the observations that are expected to be performed with cta we expect a hundred hours on each different dwarf ferroidal that will be targeted best candidate and even though we wouldn't be able in principle to reach the same level of exclusion that we have with for example the galactic center we still it's important to have this universal and complementarity between different objects now that we know about dwarf ferroidal let's go to the other extreme that is galaxy clusters galaxy clusters are the largest gravitationally bound structures in the universe and one will likely think that they are pretty stable objects however these are the last structures that I've formed in the history formation of the universe so we can get some clusters that are pretty stable like the one we have in the left side which is the perceptive cluster when we can see in color the distribution of the mass with this very pretty spherical symmetrical and then in the right hand side we have the public cluster when we can clearly see these two front shocks in the distribution of the mass that tell us about the history on the cluster and it's telling us that it has gone through some major event really recently now more things about galaxy clusters is that in contrast to dwarf ferroidal they host galaxies which account mostly up to five percent of the galaxy cluster mass they also host a lot of active galaxy nuclei this very well-known source of gamma-ray emission and they also have plenty of hot gas and dust which is usually called the inter-cluster medium and this inter-cluster medium is usually exposed to some very strong magnetic fields through a lot of turbulence that end accelerating these particles that are in the hot gas and dust and creating cosmic rays so you also will know about cosmic rays if you check on these past webinars of the series and from these cosmic rays we also expect gamma-ray emission what is uh I was curious about it is that is despite expecting them we haven't detect any kind of gamma-ray emission from galaxy clusters so just the detection of gamma-ray emission from a galaxy cluster will be a very big achievement not only for CTA but for the whole astrophysical community regarding the characteristics galaxy clusters are in the in the lightest case billions times the mass of the sun and well they are not so close to us the closest to us will be the Virgo cluster which is the 49 million light years to us and but they can appear as a really extended object to us for example the Virgo cluster it has a radius of eight degrees in the sky but some of them that are pretty far from us will just appear as a point like however did you remind you that I tell you that galaxies in the galaxy cluster only account to five percent of its mass okay this hot dust and hot gas only accounts for the 15 percent of its mass so the rest this 80 percent rest is in form of the armature so are huge huge armature-dominated objects so this is more than enough to point again our telescopes to galaxy clusters and also are the perfect environment to not test only for example this annihilation scenario model that we've been talking about but also to test other kind of models for example this decayed armature model in which we assume that a dark matter particle can indeed decay into two standard model particles for this case CTA is planning to serve the Perseus Galaxy Cluster for 300 hours and we will perform exactly the same kind of analysis that model was telling to us we were aiming for a detection and in case we do not detect the gamma rays or is not from that matter we were able we are going to be able to reject some models which will be no longer compatible with our observations last but not least I wanted to also talk about this very light components of the dark matter this model that was introduced Javier before which are the axioms the axioms as Javier has told have a mass of a billionth time the one of the electron so they are really really some light particles and we're introduced it in the standard model of particle physics in order to solve some problem related to the strong force however in some models these axioms or axiom like particles are expected to be coupled to the gamma rays are expected to be coupled to the light and in these models we can see that these axioms can be converted into gamma rays and all the way around in the presence of strong magnetic fields and just for you to know our universe is full of the strongest magnetic fields that we have so what we can do with CTA is to point to very well known source of gamma rays like for example these agents which are also trigalactic and to reconstruct the path of a gamma ray that has been emitted from one of these agents through all the magnetic fields and all of the changes that we have gone turning into this process of conversion into an axiom and then try to recover this signal and again in case that we are not able to to detect this gamma ray what we can do again is just to exclude in this plot as we can see on the right hand side the models that are no longer compatible with the observation that CTA is expected to perform so just to wrap up everything that we have talked that matter naturally despite mainly 100 years of standing it's still unknown we have a huge range of different kind of models with different characteristics and properties with different range of masses going to very very light masses like the actions that I just told you to these primordial baffles which are no longer point like particles just massroscopic objects and it's very important to have this complementarity between the different ways we want to detect that matter there is that people that is trying to produce that matter at the Large Hadron Corridor and also other experimenters that are trying to measure that if that matter is able to interact in this weekly sense with the standard matter and then we have our channel which is indirect detection with this detection of that matter through his annihilation and there's still plenty of astrophysical sources to be exploring in gamma rays and a lot to do in order to know for example these backgrounds that we have for galactic sources on even characterised better the objects that are straw-galactic like these radial dwarf galaxies that we know from very recently and for this we will have CTAO which is the future of the gamma ray astronomy so thanks a lot Judith for this super nice and detailed overview I would like to ask Javier Mabel to join us and congratulate you too I have to say I really enjoy the webinar so for the people that is watching us just as a reminder we are going to start the question and answer session so if you have any questions about what they explain or you have a question you have before this is the time send it through the comments on Facebook and YouTube meanwhile I would like to actually ask myself some questions to you I would like actually to start with Javier who was the first one you briefly mentioned a source whose name just popped up for me that it was primordial black holes I don't know if maybe you can delve into that because I'm kind of curious what is that what is the difference between a normal black hole we normally hear about and primordial black holes and why they are a target for that matter yes so thanks for the question because it's really interesting and it's a topic I like to talk about I think we could do like five webinars on primordial black holes because it's a very vast topic but very quickly what we think we know about black holes is that they are produced by the collapse of stars at the end of its life its life cycle and the pressure of the star cannot counteract its own weight and it collapses and if the star is very very very heavy it collapses a big time into a black hole this is what we think we know about black holes but there is another theory there around from the early 70s I think it was proposed that primordial black holes and that these kind of objects can be produced by stellar collapse but also can be produced in the very early universe through fluctuations of density the universe it goes through the so-called inflationary phase which is a very violent phase in which the universe is expanding exponentially crazy and these fluctuations can lead to actually very very very compact objects which are primordial black holes and the thing is that primordial black holes can effectively behave as dark matter under certain conditions and more interestingly they can evaporate through the so-called Hawking radiation due to the late Stephen Hawking and this means that black holes can actually emit some particles in the last steps of their life and can actually emit gamma rays so CTAO in principle could even detect some gamma rays coming from these primordial black holes so these are very very interesting targets very exotic objects but very interesting nevertheless and maybe this question goes to another speaker maybe Mabel how can we be sure that we detect gamma ray 100% from this source or to another source I think have you already kind of explained but the point is it could be possible to misinterpret it the data that would be another source or something yes well the quick answer would be that we can not be 100% sure like in science it's very difficult to reassure that something it's something in the case of dark matter what we have to do it's that we have to relay on other kind of science as you did say there are many ways to try to detect dark matter there is direct way indirect way etc so in the case that by luckily we detect some signal that it's compatible to any of our models for example we did a signal and we see that it's compatible with one of the spectrum of dark matter so we can say okay we think that this might be dark matter okay then we need from the support of the scientific community from other experiments from experiments from the earth from experiments from direct detection for the production of dark matter to really confirm or to really confirm that this model of dark matter is actually possible and that our signal it's really a true signal from dark matter so that that will be the way to go perfect thanks and then actually kind of discussing this part of maybe misinterpreted that it's difficult to detect and so a question to Judith you were talking about the galaxy clusters which are the biggest structures that we have in the universe and you were talking about them like a whole source that you would like to observe and so but shouldn't we consider the things that they are hosting in order to be sure we're detecting dark matter why the whole galaxy cluster that's a very good point and this leads me also to to the fact that galaxy clusters host galaxies and maybe something else right because we know from dark matter simulations that we expect from this history formation of the universe the smallest structure for example this is very large to form space and then by accretion, collapse and really violent processes they form this biggest object so as Javier was mentioned we want to look for sources which are really concentrated because the dependence on the gamma reflux that we expect from dark matter annihilation is dependent with the square of the density so of course in order to make these prospects and also to quantify in a reliable way the amount of gamma rays that we need we need to model also the gamma ray annihilation that we expect from these inner galaxies or what we usually call subhalos and substructures great I just see questions I'm going to do it very fast because sorry we are running late but we have a question a more technical one from Richard I guess he's excited to know when CTAO is likely to have the first light so well maybe I can answer from the perspective of CTAO actually Richard next year we will start the construction phase it would take well once the new entity the European one is established the construction is going to start and it will take around five years but obviously the data it will be taking actually Mabel you're working on the large size telescope prototype maybe you can say something from the first telescope we have already in place well from the first telescope we already have some data that has been analyzed and it's been very successful actually it's been taking data for now maybe a couple of years but in the latest year we have observed many different sources and it's very interesting and I hope and probably for the next telescope it's going to be faster right because always the first ones it's you it's when you have all the problems but then once you know that your telescope works I think the next will be much more quick and by the moment that we have more than one and we can observe in a stereo that will be awesome a lot of data a lot of interesting science that we can start doing even with just even with just some telescope and not all the the array yeah I think we are all exciting to to see the data not only from one but from the from from all the array the sensitivity all the course that you show that is going to be amazing okay we have another question um I would like to do it sorry guys I know it's late but Malvernudet a Scandarch method we compose by antimatter so whoever wants to answer maybe Javier you start also talking about the decays and so yes so short answer unfortunately not we would love to because we will have our our mind much much quieter but it's not um the problem is that antimatter is very very similar to matter actually it comes from the same process let's say if you have a positron which is antimatter it's the antimatter of the electron but you can also see this from the perspective that electron is the anti positron so they are symmetric under this under these things actually that matter interaction as we saw produce cosmic rays and cosmic rays are also antimatter so antimatter is well known since more than 100 years ago since the time some 40 back so it's very well studied and unfortunately cannot be dark matter because it it doesn't fulfill the the things we need for dark matter to behave the way we know but it would be very very nice okay so thanks again guys I think this was the the longest webinar we have I really enjoy I have to say um and we are going to finish already here I would like to thank you again thank also the audience that join us and just remind them that we have next month another stop in this journey through the extreme universe we're going to talk about transience the most powerful sources that we have in our universe so do not forget to subscribe to our facebook youtube twitter all the social medias in order to stay tuned so thanks again and see you next month ta ta