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Radioastronomia – Astronarium odc. 1


Giant antennas pointed at the sky. These are some of the most advanced and unusual tools in the hands of scientists. What are they used for? How are they built? What are they supposed to find in space? In this programme we are going to answer these questions. Welcome to ‘Astronarium’. RADIOASTRONOMY What Is the connection between space research and… a radio? It might seem there is none. An American engineer Karl Jansky didn’t think there was one when in the 1930s he was given a task to identify the source of noise in radio signal. Jansky built a special antenna for this, but when he completed his measurments, it turned out, that apart from the radio noise generated for example by thunderstorms there were also noises the source of which he could not identify. It seemed, these noise weren’t generated by anything on Earth. Now we know that Jansky detected the radio signal of the Milky Way. This discovery gave way to a completely new chapter in space research. Radioastronomy became the source of some of the most important discoveries in the last 100 years.. And what can we find out listening to signals from space? This is the question we are going to answer today. This is Astronarium A programme about the secrets of the Universe and Polish scientists who explore them. My name is Bogumił Radajewski.
Welcome. – Please do not adjust your receivers. This scratching sound is not static. This is the radio signal of a pulsar, a star which died centuries ago, its core collapsed when the star exploded as a supernova. Now the star sends regular pulses into space, just like a space lighthouse. However, the star is difficult to observe because its signal fades among many other signals that reach Earth all the time from billions of different radio sources in space. – The problem is how to recognize and understand something from this, so to speak, ‘chaff’ coming from space. And why am I saying this here in Cracow? This is where Polish scientists faced this problem for the first time and built a radio observatory almost sixty years ago. Fort Skała in the suburbs of Cracow. A fortress from the times of Austrian annexation turned into one of the biggest Polish astronomical observatories. 60 years ago a group of explorers recorded here first radio signals coming from space. Those pioneers were led by professor Adam Strzałkowski. – I decided that the first thing to do at Skała Observatory, was to build a radiotelescope. The plan was to start with observing radio signals from the Sun. It was 1953 and there was going to be a solar eclipse visible in Poland in the following year. The problem was we didn’t have a radiotelescope. I knew from my own experience that during World War II Germans left radio antennas at Cape Hel. It all ended with interrogations by the Secret Police. How did we know there were such antennas there, what’s more, how did we know what they were for? Anyway, it was a failed attempt. And so, we had to get a radiotelescope. A radiotelescope which could be located at the new Skała Observatory. – Did you have to build it yourselves? – Yes, we had to build one ourselves. We decided that our radiotelescope will have a 5 meter diameter and Mr Kowalski prepared such a project for us, assigning mirror construction to a welding company in Cracow, owned by an engineer called Wolfram. It was amazing, that Wolfram finally managed to create a welded pipe structure with 3 milimeter accuracy. Our observations were not very accurate, but it should be noted that they were first radioastronomical observations in Poland, conducted with a device built exclusively for radioastronomy. – To understand the secret of radioastronomers, you need to realize how the world would look like if our eyes could register more than just the visible light. The world would look completely different. – If we could see electromagnetic radiation in all of its range, the world around would be filled with all kinds of waves invisible to the naked eye. Radio, television, mobile networks, and WiFi are things which are created by humans. But the Sun would also look completely different, observed in infrared, ultraviolet, X-rays, or at radio frequencies, such as observed 60 years ago by astronomers in Cracow, it would not look much like the daily star that we know. It is the same for all space. This is how the image of M87 changes when we move from visible light to an image created with radio waves. Much of what happens in different reaches of the Universe escapes human sight. However, the fact that we cannot see something does not mean it cannot be detected. – If we had, let’s say, a receiver, which was meant to see like our eyes, optical wavelengths, but within radiowave range, we would need eyes few hundred meters large. However we can build instruments which enable us to peer into space in a way completely different from astronomers observing the universe in visible light. – How does this radio Universe look like? – The radio Universe turns out to look completely different. First radio surveys conducted after World War II showed existence of objects, never considered before. It turned out we were observing some spots very bright spots in the sky, looking very much like stars. But these were not stars. At first they were named radiostars. But observations in visible light showed no such objects. They were quasars. Today we know that they are cores of active galaxies. At the centers of those galaxies, showing such unusual activity, lie supermassive black holes. They can reach masses billions times the mass of our Sun. – It were also radioastronomers who managed to confirm some theories. For example, the theory of how our Universe came to be. Right? – Yes. It was an astonishing discovery. They discovered noise coming from all of the Universe. For many weeks they worried that something was wrong with their instruments. Finally they reached a conclusion that the noise coming from all the Universe was in fact radiation, and they quickly managed to explain that it was background radiation of the Big Bang. – Radioastronomical research is somewhat like an attempt to listen to a radio programme broadcasted somewhere from the other end of the world with – let’s say – a toaster. To receive such a signal, we need a really decent antenna. An antenna like the one we are standing in. – This is the largest radiotelescope in Poland and in middle-eastern Europe. A 32-meter diameter antenna was built by scientists from Center for Astronomy at NIcolas Conpernicus University. With this instrument installed in Piwnice near Torun some of the most advanced research in the world can be conducted. Its enormous dish is expected to collect and focus in one point as much cosmic radiation as possible. However, size is not the only secret of this unusual instrument. Inside, we can find real space technology. All this equipment is supposed to make the elusive signals from space turn into something that can be registered. We were given an exceptional opportunity to see it from the inside. – We are in the heart of the radiotelescope, little above its elevation axis, the axis on which the radiotelescope rotates horizontaly to Earth’s surface. This is called the focus chamber. This place focuses all electromagnetic waves collected by the radiotelescope’s dish. Electromagnetic waves fall into elements called gaffers, into this, let’s say ‘pot’, the so called diuar. Inside the diuar there is very fine vacuum measuring about one militorr. This keeps the electronic equipment inside isolated thermally from the environment and we can successfully cool it down to very low temperatures, even to about 8 degrees on Kelvin scale. This is around minus 265 degrees Celsius. The electronics itself has such properties, that it generates noise signal. This happens because it has a temperature higher than absolute zero. It turns out that with lower temperature of preamplifiers and receiving systems we get less noise generated by the electronics. Why do we want to minimize this noise? Becasue natural signals that we receive from space, have also noise-like character and we are not able to distinguish betweeen them and the noise artificially generated by electronic systems. Therefore, the less noise a radiotelescope produces itself and the less noise is generated by preamplifiers, the more sensitive the telescope is and the weaker signals we can receive. The faintness of these signals can be understood in the following comparison: if we were to gather all the energy collected by all the radiotelescopes in the world, operating from the beginning of the 1950s, so for over 64 years, it would be enough energy to melt a single snowflake. This is how weak are the signals emitted by natural objects in space. Large sizes of contemporary radiotelescopes allow us to detect even very faint signals coming to us from space. However, reaching high sensitivity is only part of the problem. Even the largest antennas suffer from yet another problem. – In general, radiotelscopes, to speak in plain language, work somewhere between listening and looking. If we point a radiotelescope to a specific location in the sky with a source of electromagnetic radiation, we can observe how bright the source is, we can pretty accurately determine the direction from which radiation is emitted, but we are unable to say practically anything about its shape and distribution in the sky, so generally what a radio image could look like. – In other words: radiotelescopes see everything as if through a fog. The image is almost completely without details. Why is it so? To understand this we have to talk about physics a little. Radio waves have much greater wavelength than visible light. Therefore, to detect them with similar accuracy, we would need a much bigger instrument. The difference is so huge, that even the largest radiotelescope in the world ‘sees’ with worse quality than humans with their naked eye. To sharpen the image we would have to build a gigantic antenna with a diameter not in meters but in thousands of kilometers. However, astronomers found a solution to this problem. With the use of interferometry they learned to combine a number of smaller antennnas into a larger one. – You could imagine it like this: if we take two radio receivers, – be it radiotelescopes or simple radios, it does not matter – and we set them to any location in the sky or to any radio station. If we record the signal collected by these two receivers, then, due to fact that the speed of light has a finite value, at the very same moment these receivers gather different signals. Combining all these signals, and in fact from mathematical calculations of the differences between these signals at a given moment, we can re-create the actual distribution of radiation in the sky. To speak plainly, if we have two radiotelescopes, looking at any given point in the sky separated by, let’s say, 100 kilometers, we can create a virtual eye, with a sensitivity which would theoretically equal the sum of sensitivities of these two radiotelescopes, and the size of this eye would be 100 kilometers. So if we take telescopes located all over our continent, we can get a radiotelescope the size of our continent. At present, we also have a small Russian antenna in space, and we are building a telescope 3 to 5 times larger than our planet. This is the largest scientific instrument used by our civilisation so far. The radiotelescope at Piwnice is also a part of such international research instrument, the so-called European Very Long Baseline Interferometry (VLBI). Its combined antennas offer such high resolution, that they could read headlines of newspapers lying on the surface of the Moon. Astronomers are using this system for some of the most detailed studies of distant objects in the Universe. – Excuse me, doctor, am I to understand, that you are responsible for such research, in which you were studying space in search of… alcohol? – That’s right, athough it was methanol, and not commonly known ethanol. Methanol, a CH3OH molecule which forms in regions near a developing young massive star, a star which may end its life as a supernova or a black hole. Only at 5 cm radiowaves, coming from methanol molecules, which emit them, can we find out about the environment around a young massive star about to be born. Its environment is too dense with gas and dust for visible light to reach us. But radiowaves are capable of getting out of such cocoons of gas and dust, reaching us and telling us what is happening there. My discovery showed, that actual methanol maser emission develops in such spherically symmetrical structures, so there has to be something inside. Thus this emission occurs around a newborn star. This is a form of a ring, with a diameter of 900 AU, so about 900 times the Earth-Sun distance. It is located in the Crux-Scutum Arm of our Milky Way Galaxy. Our Sun is somewhere here. The distance is 3 kiloparsecs. – I know, that at first glance it is hard to realize, but I am in area which may soon become the location for the most advanced radio research in the world. It is here, deep in Bory Tucholskie National Park, Polish scientists would like to build a radiotelescope, with a size which would dwarf everything we have seen so far and which would allow us to peer deeper than ever before. I am here to meet one of its creators. This is Hevelius – potentially the largest radiotelescope with moving dish in the world. Over 100 meters wide and as tall as a 30-storey skyscraper this radiotelescope would overlook the forests from an inconspicuous glade hidden far from the civilisation. Professor Andrzej Kus is the leader of a consortium which develops this gigantic project. This is the place where we want to build one of the largest radiotelescopes in the world. A radiotelescope with a dish diameter of about 100 meters. This offers much larger collecting surface, and therefore, a much higher sensitivity. That is why we could reach further into space and receive weaker signals naturally generated by different objects in space. Large collecting surface allows for observations of the most distant, earliest objects, which appeared in the Universe right after the Big Bang. This is a study of the evolution of the Universe from its beginning to present era. But a radiotelescpe does not only mean scientific research, it is also a development in receiving technology: radiolocation, communication, navigation. Everything that is connected with modern research in space. – So far Hevelius found its place on the so-called ‘roadmap’ for Polish scientific investments. But this is not the only brave project. 20th century radioastronomical research has given over 40 discoveries honoured with the Nobel Prize. This is more than any other field of science. Therefore all over the world new observatories are being built,
larger and larger antenna networks and completely new ideas on how to receive signals from space. Thanks to this astronomers will be able to better understand the secrets, which cannot be seen but can be… heard. – Since the first radio observations, through some of the greatest discoveries of the 20th century, to the latest research projects. Radioastronomy continuously proves that the Universe hides much more than meets the eye. But science is not everything… This is music, created with the use of signals detected by radiotelescopes. Let these space sounds be our conclusion. More news on space research can be found on Astronarium website. We will unravel new mysteries in our next episode. See you next time! Production: Polish Astronomical Society (PTA) and Polish Television (TVP) Transcription: Krzysztof Czart
English translation: Mariusz Herbich www.astronarium.pl
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