 I assume some of you asked yourself what does the life of an astrophysicist look like? This topic is very interesting. Today we have Katrin Bergmann from the star of the Rete Hamburg. She'll talk about how every day looks like, historically, what the research looks like. And they also have a cat there, I think it's very interesting. Yeah, thank you for the invitation. My name is Katrin. I work in Hamburg at the observatory as a scientific employee. I write my doctor thesis there. I will talk about the observatory. And first I'll talk about the history of the observatory and talk about what we do today. And yeah, let's start. We have Johann Georg Rebscheut at the end of the 17th century, 1700s. He was the spritzenmeister of the firefighters in Hamburg. He was very interested in stars. And he was the first one who founded the observatory in Hamburg. It was a private observatory at the Stindfang for those who live in Hamburg. And he observed the sky. This observatory in 1811, sadly, was destroyed. But he also initiated that it was the first city observatory, star observatory. And navigators were educated, which was also important for naval operations. This is also part of the Hamburg history. Johann Georg Rebscheut in 1830 died, sadly. But he also, thankfully, fully saw that the observatory was founded. There's a lot of things that are named after him. There's also a boat in the haven that also says oba spritzenmeister Rebscheut. And his children also continued this tradition and used optical instruments that also were used for astronomers and also for navigation and so forth. All right. This was the first star observatory in Hamburg. This was also the millen-tor. Since 1833, this was a national institute, also funded by the government. And this is also why the haven in Hamburg, because it's important, as I said, for navigation also for the time. But at the end of the 1800s, it became clear that this location wasn't possible to be used for research because it became brighter and brighter. Also with electrification and more and more lights were used in the city. We thought about where we would choose a new location. And today, this is also a Hamburg history is also observed there. In 1906, we started to build the Bergdorf Observatory. In the past, you can see on the photo, nothing was around there. Today, there's a lot of houses. And this was an ideal location for an observatory because also was on a hill and because in the past, there wasn't so much around. It was an ideal location. It was built between 1912. It was a national institute for a long time. Until in 1968, it has been integrated to the University of Hamburg. Since 1996, the observatory is under protection. And there's also a try to make it a world cultural heritage. But it's not yet really predetermined whether this works and would be nice if this would work. Okay, now we have a few images of how it looked like in the early 20th century. So 1913, one year after it was inaugurated, two of the largest telescopes that are still on site were inaugurated too. We have this elongated one that is this large refractor that is a lens telescope. And it was one of the largest in Germany at the time. On the left, we have a mirror telescope, which works a bit differently, which I'm going to talk about later. But these two were then put in place. And what was new with this observatory is that there were separate buildings for each telescope. You can see in the background here, there are individual telescopes in each building. Before that, in the 1800s, things were different. He would put these telescopes onto the roof of a larger building. But the larger the telescopes became, the less practical that became, and there was a need for individual housing. And also due to the air movement generated from the heating, if you would relocate these telescopes to individual buildings, you would then be able to build them without heating so that the conditions would be more ideal. And the Begudov Observatory was one of the first to have separate buildings for its telescopes moving on. So I just mentioned that there are basically two kinds of telescopes. You have mirror telescopes and lens telescopes. The mirror telescopes work like this. You have the light beam coming in. The main mirror reflects and collects the light, bundles it onto a secondary mirror. And that mirror then reflects it back to the ocular or eyepiece, or in current times it would be a CCTV camera, perhaps. And in contrast, we have the lens telescopes, which are similar to simple binoculars. The amplification works through lenses, not mirrors. And the light rays go through these lenses. The second lens deflects them a second time into the ocular or the camera. And in the early 20th century, these two were kind of in competition with each other, but it became clear pretty early that mirror telescopes were the better and more practical solution because you were able to achieve higher resolutions and the binoculars you would have to make longer and longer. And you can imagine that with increasing weights, things wouldn't be as practical anymore. Longer telescopes that are very thin are not that easy to build. It's ability is the issue here. And with mirrors, you can just increase the diameter. You don't have to increase the length of the tube. Now these days, the ELT, that's the extremely large telescope, astronomers like to have these interesting wordings for their telescopes. The ELT has a 40 meter diameter. And current research has mirror telescopes as standard. The Hubble Space Telescope and others, they all use mirror telescopes. And lens telescopes are used for amateurs, but not professionals anymore. And the other issue with lenses is that there might be chromatic errors. Colors might change because the different wavelengths reflect, deflect it differently. And that creates inaccuracies in the image. So these days mirrors are dominant. And I now have a few slides about the largest telescopes we currently have. Reflect refractor here, that's how it looked like in the past. In recent years, the whole building was renovated. You can see the wooden paneling in the dome. And you can see that the Repsoled Company, which is the descendants of the founder, they built this. And you have this mechanism that lifts the telescope up. And it can be moved up and down this way for increased flexibility for finding all these various places. And that was built by Carl Zeiss Jena, a company you may have heard of. And the whole telescope has a 60 centimeter lens and nine meters focal length. Then we have the one meter mirror telescope, which is also from 1913, just like the large refractor, the large lens telescope. Again, built by Carl Zeiss Jena. And this is how it looks. You see, it's more compact than the lens telescope. And when it was built, it was actually the largest telescope in Germany and the fourth largest worldwide. And it's very heavy, 26 tons, is its weight. But there wasn't as much electronics back in 1913, but it can all be operated by hand. The transmission has been built this way. There is a count of weight. And these are all used for observation today. And by us employees, if the weather plays along, we can then do observations, whatever we like. But for research, this kind of equipment isn't used anymore because current opportunities are so much better. But it's still very nice to have these and show people how things work. We have one more modern telescope, the Oskar-Lüning telescope. Another mirror telescope works quite the same as the one that we saw in the earlier slide. But this is digitized. You can control it at home using your computer. You don't have to turn levers or anything like that. It's controlled by a Raspberry Pi. And this one is used in internships in the physics education. And you're in university. During the course in university, you will have to have an internship in various research institutions. And we are one of those, and controlling the telescope and making observations with it is part of that. So it's actually used not for current research maybe, but it's used in the university sector. Right. I'll get to the topic of today, what the research focuses on today. I'll talk about it. You can see our nice main building. There's also a library in there. And on top, we have an own separate radio telescope that's also done by physics students for their internships. We do a lot of radio astronomy with low-frequency array telescope. I'll talk about this later because that's a radio telescope that we also have a site in Nordostadt. There's also an internship trial with the three-meter radio telescope on the roof. What we are also doing, we also do X-ray astronomy, infrared astronomy, and also partially optical astronomy. We cover almost all, so most of the research fields. I'll talk about this more in detail now. X-rays, radio, and so forth. The telescopes I talked about before, the refractor, those are making optical observations. For a long time, this has been the main field of research of astronomy. You look at stars or galaxies just like with your eye. This means we here have the light, normal light, have certain wavelengths that our eyes are trained to. Those are wavelengths in the nanometer area. We have this range that we can see with our eyes. But the electromagnetic spectrum, those are just wavelengths that are very different. It's just lights that our eyes can capture. We need to build separate devices, for example, for X-rays or radio waves so that we can look at them. So we also have what the atmosphere, how penetrable the atmosphere is for certain wavelengths. We have the locked gamma rays or X-rays, waves with very long wavelengths that they can't get through. That's actually good because it protects us humans from these rays. But so for us to do X-ray astronomy, we need to build telescopes on satellites. And they have to be put outside of the atmosphere on the satellites. And they're outside of the atmosphere. They take the pictures. And we can download the pictures from the satellites and do astronomy, X-ray astronomy. And it's pretty similar with infrared. Some of you might have noticed that the James Webb telescope has launched on the 25th. This is also an infrared telescope. And that's because it's also not infrared light. It's also absorbed by the atmosphere. And that's why it has to be outside of the atmosphere. We also lucky that there's a large area of radio waves where the atmosphere is transparent for those. And we can build this observatory on Earth. And there's been a large field of research because with radio waves, we can also observe very massive black holes at the core of galaxies, which we can't do with optical telescopes. Also this picture of the black hole a few years ago that has been very much in the public eye. This is also a radio picture. Yeah, I've explained this now. We also have the lofa that I've mentioned before, the low frequency array. This is a radio telescope. It has several locations all throughout Europe. And one is also in Nordostadt. It's a radio telescope. It looks completely different from a telescope that you can look through. It's just a bit of antennas. These are pictures of the field in Nordostadt. There's an array out of 69 antennas. And these antennas are the radio telescope, part of the radio text. This technology is pretty simple. The IT behind it is not that simple because it generates a lot of data. Because you can imagine 96 antennas, they all receive the data. But we also have to calculate all the different combinations. And there's very large data volumes that have to be processed. And that's why the station at Nordostadt, we had separate fiber optic cables. It doesn't really look spectacularly. There's just a container where all the cables come together and they get transported further from there. I also have some numbers here. It generates 10 terabits per second. And we have a 10 gigabit connection there so that we can have proper connection. This low frequency array is being expanded with new locations. And yes, but you can imagine the more stations you have and the farther they are from each other, the better the resolution you can achieve. You can imagine if you have just one telescope that has such a large diameter. A large diameter means a better resolution. And this also means that you have a better image in total. That's what we want. This was the radio. I'll just get to X-ray telescopes. I'm working on this particular project. I do X-ray astronomy, not that much radio. This is the project Erosita. This has been started in 2019, not too recently. This is also cooperation between Germany and Russia. And this is a radio telescope. It's on a satellite. It delivers us data already since for two years. It scans the entire sky continuously. It takes pictures of the entire sky and receives radio X-ray rays. We have 0.5 to 10 kiloelectron volts. We also observe objects like galaxy clusters that are really big, but also very far. And these galaxy clusters emit X-rays. And then we can observe with this telescope. This has been done by the Max Pank Institute for extraterrestrial physics. And this is a big project. And we can be very curious what is still being discovered there. The galaxy clusters, I've talked about that. What do we do with these X-ray and radio waves? It's interesting to look at objects. What does this look like in the X-ray as well as in the radio waves? The galaxy clusters are a good target if you want to look at large structures because galaxy clusters are very large clusters that are bound gravitationally. Galaxy clusters consist of 50 to 1,000 galaxies. And those are gravitationally bound. And they build blocks in the universe. If you would zoom further out, you would see these blocks of galaxies that spread. And because these are large, continuous objects, you can look at them even if they're very far. And this is analogous to being early in time because they're far away. We can also see how they look like right after the Big Bang. Or not too shortly after the Big Bang. And we can look at how the universe looked in the past and how did it evolve. So you can see in the optical spectrum, it doesn't look that good. But because of the gravitational forces, the gas between these galaxies is being heated up so much that it shines in the X-ray area and also in the radio waves. This means that in these galaxy clusters can be easily found through X-rays. And you can do comparisons. How does it look like in different wavelengths? And you can learn at best how the universe developed and how did it form. I have one other topic. Many of you will know from classical physics there is always this distinction between theoretical and experimental physics. And in astronomy, it is somewhat similar. I work on real data used by the telescope that I talked about earlier. That's what I work with. So I am an observational astronomer that is the equivalent to the experimental physicist. But the astrophysics has a theoretical side as well. These are people that run simulations. Computation astrophysics is how they call that. They simulate the universe using various models. And we can then see how well do our observations, our discoveries, fit those simulations. So the people running these simulations come up with a model saying this and that is the basic forces and my initial conditions. The starting conditions. And I then add a few physical laws to that and see how the whole thing changes. And we can then compare that with our observations and see whether the model suits the observations or not. And that's what you can do. Right. We call these n-body simulations meaning that you have a certain number of particles that you start with and that you work on and you can run Monte Carlo methods or things like that. And that is a very computationally intensive kind of research. And it has developed a lot in the last few years because, of course, you can do amazing computations these days that you couldn't do 10 years ago. A very large computing center is in the city of Julich in Western Germany. That's what the image here is showing. It's UL's Computational Center. You can run parallel computing here. And high performance computers can be used for these tasks. And we have a very famous simulation that is the Millennium Run. This project has been in existence since 2000. And in 2005, I had the first run on 2160 to the power of three number of particles. And you cannot say that one particle would represent one billion solar masses in dark matter. That's what you can say. One particle. So you don't see galaxies developing but dark matter. So one particle represents one billion solar masses of dark matter. And you can insert these irregularities and see how it develops using the physical laws that we have. And you can zoom in. You can see these networks, these clumps. And that's what you can observe as well. That was run on a supercomputer in Garching in southern Germany in Bavaria. It took a month's computing time, 25 terabytes of data. And in 2010, it was upgraded with the second run to 6,720 to the power of three particles. And the computer Europa, or duropa, which has 12,000 cores, that was equivalent to 300 years of CPU time on another computer. So you can see how there is a lot of potential still in this kind of research. So having theoretical astrophysics and having ever better means for comparing those results with observations. And that gets me to the end of my talk. I've collected a few links for you. I have the universities, the supporting association. And I'm available for questions. A 3D walk through the observatories. I hope you found it entertaining and interesting. And I'm looking forward to your questions. Thank you so much. I've been a few questions in the chat already. And I'm sure there are more to come. I'll start with the first question. First one is about the dome in the observatory. Is the dome, actually, can you track the sky's movement? You can control it electrically, yes. Next question about the radio telescopes. How can you filter out the terrestrial signals? Surely they are much stronger than everything. That is actually quite complicated, yes. There are very complex calculations that are used here. That's a very good question. But there are good models that you take these data out. And it's very complex. And there are people working on that full time to filter out the disturbances, the signals from the Earth. So it's the same wave things. Surely you really have to do the calculations. Yeah, there are some parts of the radio spectrum that are kept free from terrestrial signals. But it's not that simple. And there are disturbances in radio astronomy. You really have to live with that and try to deal with that and filter it. OK. Have there been cases when people thought they had observed something and then found that it was terrestrial? No, actually it's quite clear to see every time terrestrial signals can be discerned. OK. A question about the observatory. In the past, apparently the idea to relocate the employees to the DC in Barenfeld in Hamburg, is that still a debate? No, it's not. But yeah, the thought had existed. And it's actually fairly natural because we don't use the telescopes anymore. We are in front of our computers all the time. So it wouldn't really matter where we work. But still, despite being historic, it is worth upkeeping and for inviting people in for evenings and to be sitting there as astrophysicists. So the thinking isn't anymore that we would be relocated. I have a remark as well. Nothing has been said about the cat. Can you comment on the cat? I don't know. We have a cat that is running around and likes to be fed by everyone. It's gained and put on a bit too much weight. And it lives here. And with every talk, every dissertation, he's defending the cat in the first row and likes to take part. Oh yeah, please bring the cat along to the next real CCC. OK, are there any more questions from the chat? I'll check. Otherwise, we would switch over to the extended Q&A, which will be in German and not interpreted. I see a lot of joy that the observatory is being maintained. And of course, we are very happy about it too. It's a very nice location. Everyone who would like to visit if you are in Hamburg or its surroundings, it is publicly accessible. You can take a walk there. And there are these observation evenings. Just check the website. I don't know how things are regarding corona, but it's really worth a walk. Go there. Take a Sunday stroll. Note it. Yes, thank you. That's it for now.