• An old lady helps out

    Searching for stardust

    It seemed as though the telescope at Westerbork was done for. But thanks to a hypersensitive new camera, it can now look for stardust.
    in short

    It looked as though the radio telescope at Westerbork was going to be demolished, but it has been given a second chance.

    By implementing new technology into the telescope – which consists of fourteen dishes spread out over a distance of three kilometres – it has been turned into a hypersensitive camera.

    It is estimated that ‘Apertif’, as the camera is called, will be searching the heavens for signals from space from December onward.

    RUG astronomer and Vici grant winner Marc Verheijen is going to be analysing Apertif’s output in order to ultimately map how hydrogen gas – the universe’s basic building block – is distributed.

    Verheijen also hopes to find out how hydrogen moves inside galaxies within the ever-expanding universe.

    New technologies have made the equipment a lot more sensitive than before. While so far ‘only’ slightly less than a thousand galaxies have been explored, the researchers expect to be able to explore approximately a hundred thousand galaxies in the next four years with the help of Apertif.

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    She is quite an old lady already. And it if weren’t for this project, she would definitely have been done for three years ago. ‘Isn’t it great that she is getting a second chance? That she can be of use to science for five or ten more years?’

    The old lady in question is the radio telescope at the Westerbork Memorial Centre. The project: a special hypersensitive camera that – if everything goes according to plan – shall be searching the heavens for signals from space from December onward. Marc Verheijen is the man who will decipher these signals. The RUG astronomer personally dragged a Vici grant away from the jaws of hell, which means the project can finally begin.

    Verheijen successfully sued to secure the NWO funds that had earlier been denied, even though the application received high marks for quality. A judge ruled it had been wrongly dismissed.

    A lucky break, because after having spent ten years of labour and various grants on the development of an astronomical instrument – that enlarges the scope of the elderly Westerbork telescope by a factor of thirty – not being able to use it due to a lack of additional funding would be madness.

    Malfunctioning parts

    Thankfully, it never got that far. Westerbork is currently a hive of activity. Dishes are being cleaned: they were covered in a green layer of gunk and were rusted. Malfunctioning parts are being replaced, such as the cogs in dish two that was suddenly completely ‘out of zenith’ – it was no longer pointed at the highest point of the sky. ‘It had completely shifted the other way!’ senior technician Jan Pieter de Reijer enthuses when Verheijen arrives at the telescope. ‘We never heard or noticed anything, but when we were figuring out what was going on, it turned out the bearings had been ground to pulp.’ He rubs his fingers together to show how the parts felt when they opened up the metal housing.

    It’s no surprise that they were behind on maintenance. The dishes – fourteen of them, each 25 metres across and spread out over a distance of three kilometres from east to west – have been in operation for 45 years. Once, they formed one of the most advanced telescopes in the world, but Westerbork was surpassed by more sensitive equipment elsewhere and was in danger of becoming obsolete. But once the technicians have finished stripping the enormously tall structures and outfitted them with new, high-quality equipment, the telescope shall once more be cutting-edge technology.


    The camera – christened Apertif – is in actuality a box measuring a cubic metre in which 121 antennae that are each positioned slightly differently have been placed. By cleverly combining the signals, the camera’s scope is thirty times larger than it would be with just one antenna. It is a type of wide-angle lens, then, that specifically ‘listens’ for hydrogen gas in the universe.

    By utilizing a rotating cube, this film shows the distribution of hydrogen gas by tidal action in a galaxy. The third dimension reveals the movements within the gas. Films such as this will be made for tens of thousands of galaxies. (Courtesy of Mpati Ramatsoku and Davide Punzo)
    And that is useful. After all, hydrogen is the basic building block of the universe – an atomic nucleus containing only one proton and one revolving electron. It is the stardust that forms the basis for all matter that came into being after the big bang.

    Verheijen finds it fascinating. ‘Once, right after the big bang, hydrogen was divided evenly across the universe’, he says. ‘But then – because of gravity – it started to clump together. Protostars, stars, and galaxies were formed, until the universe looked the way it does today.’

    Evolution of the universe

    This process of attraction and clumping, which continues to this day, can tell us a lot about the evolution of the universe, the formation of galaxies, and what is in store for us. Why are galaxies in relatively empty parts of the universe often shaped like flat spiral disks, while those in busier neighbourhoods are more elliptical, like a rugby ball? And what is going to happen in roughly 2.5 billion years, when our Milky Way and the neighbouring Andromeda nebula – which is racing toward us at a speed of 300 kilometres per second – collide and merge? It is expected that they will form an elliptical galaxy together. But is that really true? And how will that work?

    ‘You can map the division of hydrogen gas in the universe really well by listening to the 1420 MHz frequency, which is the specific wavelength of the radiation generated by hydrogen gas’, says Verheijen. ‘But you can also look for how hydrogen moves in galaxies in the ever-expanding universe.’

    This image illustrates the distribution of hydrogen gas in a discoid galaxy as seen from above. The image on the left shows the spiral-shaped distribution fo the stars, and the image on the right shows the distribution of hydrogen gas at the same scale: the gaseous disc is much larger than the star disc. (Courtesy of Rense Boomsma)
    all, the faster the gas is moving away from us, the lower the frequency that we perceive. This phenomenon is called the Doppler effect – you will know it from a police siren. Moreover, hydrogen gas reaches far beyond the ‘visible’ boundaries of a galaxy and is therefore much more sensitive to tidal forces.

    Suppressing noise

    However, it is not easy to study hydrogen in the universe. That is because the radiation from the gas is almost imperceptible. ‘If you were to put to use all the energy that has been collected in Westerbork in the past 45 years, you would be able to light up a bicycle light for two seconds’, Verheijen illustrates.

    The measurements, therefore, are full of noise. The single antenna that the telescopes used to use had to be cooled constantly with liquid helium in order to suppress that noise as much as possible. Additionally, a great deal of measurements had to be taken to get results. For example, if you wanted to study the Andromeda nebula, the old system had to measure 163 points in the sky.

    This is why less than a thousand galaxies have been properly studied up until now. ‘Not nearly enough to be able to draw any compelling conclusions’, says Verheijen. ‘Besides, those galaxies had been selected ahead of time and were not a random sampling.’

    Impressive tangle

    With Apertif, this is a thing of the past. The new camera only needs four measuring points and liquid helium is no longer needed. This means that over the next four years, approximately a hundred thousand galaxies can be studied, and ten thousand can be studied in detail.

    And that is why today, dish six is not aimed at the sky, but angled forward. A blue cherry picker has driven right up to the edge and rises in fits and spurts until it is right in front of the heart of the dish. A technician opens the doors to the box and reveals an impressive tangle of black wires that will later send all the data downward, to the shipping containers full of data-processing equipment, after which the data from all the dishes are brought together at the central research centre.


    Now that the first six dishes have almost all been converted, it is time to start testing and calibrating. And then, somewhere in December, Verheijen will aim his cameras at the Andromeda nebula for the first real measurements for a test case. ‘We know what to expect from Andromeda’, he explains. ‘Besides, that galaxy is close by and we can form a better impression of the division and movements of the hydrogen gas. This will allow us to demonstrate the power of Apertif.’

    Six more dishes will be converted in the spring. And then? Then, the postdoctoral researchers and PhD candidates can really get to work. Because, as Verheijen says: ‘An astronomer is an explorer of the universe. And there is so much to study. After all, Columbus wasn’t satisfied with just Europe.’

    Four years. And then?

    Verheijen’s project will be completed in 2020. What will happen to the telescope in Westerbork after that is not certain. By then, in Australia, the Square Kilometre Array (SKA) will be built: a gigantic telescope that is one hundred times larger than any current radio telescope on earth. Studies that are now done with the Apertif telescope at Westerbork can be done faster by the SKA in 2024. Nevertheless, the millions invested by the European Union and research financier NWO are money well spent. That is because Apertif is a so-called pathfinder project. It is meant to demonstrate all the things that are possible with this technique: the combination of radio signals. With this, astronomers at the Kapteyn Astronomical Institute and the engineers at ASTRON hope to be in the position to become an important partner in the SKA project.