Each of the 66 telescopes at Alma has now been equipped with Chalmers receivers.
The ALMA telescope consists of 66 dish antennas located 5000 meters above sea level in Chile on a high plateau in the Andes. The dishes work linked together as one telescope and can make far sharper observations than individual radio telescopes can do.
Each of the 66 antennas has several receivers for observation at different wavelengths. The Chalmers receivers now being used allow observations of light with a wavelength of between 1.4 and 1.8 millimeters – known as Alma’s Band 5. This is microwave radiation, which can be compared with visible light whose longest wavelengths are around 740 nanometres (less than a thousandth of a millimetre).
“At these frequencies we can observe cold parts of the universe. For example, regions where stars and planets are formed are of great interest. When ALMA's dishes work together, you get significantly higher resolution than you can do with current optical telescopes, "says Victor Belitsky, whose research group is part of Onsala Space Observatory at the Department of Space, Earth and Environment.
- The frequencies that are now accessible can give scientists for example a new understanding of how stars, planets and galaxies are born, he says.
The receivers were developed by the GARD group (click on the image for a larger version with all names) in a project funded by the EU program EC FP6
in 2006-2012. The timing proved to be perfect. When the first receivers were ready, new research areas were opening up that specifically required ALMA to be able to observe in Band 5.
Victor and his colleagues had completed six complete receivers, but to handle the order for a further 73, a team from NOVA (Netherlands Research School for Astronomy) was invited to participate. They integrated GARD’s components in the receiver cassettes.
"Their effort was important to complete the delivery, but the major challenge was to develop the receiver and manufacture the components. We are delivering to the world's best and most advanced telescope, and thanks to our knowledge and experience, they have now got the best possible receivers”.
The biggest challenge in the production of receivers for radio telescopes is how to reduce noise from their surroundings and get as clean a signal as possible.
“The noise sets the limit for how weak signals can be detected. It’s like finding the right station on a regular FM-radio, but a million times more sensitive! So, the more we can reduce different types of noise, the more we increase the possibilities for new discoveries in space”, says Victor Belitsky.
For example, the receivers operate at -269 degrees Celsius, four degrees above absolute zero, to counteract interference from thermal radiation. The image shows the receivers housed in their cryostat, which is designed to maintain such low temperatures.
Reducing loss of signal in Earth's atmosphere is also the reason that the ALMA telescope is located at 5000 meters above sea level, in one of the driest places in the world. There is very little water vapor in the atmosphere above the telescope, which means the Band 5 receivers can look for water in space, both nearby and far away, Victor Belitsky explains.
"There are many uses for our receivers, both in our solar system and in distant galaxies. It depends on which research applications and topics the Alma Research Committee selects, but we know there is a lot of interest to observe water in our own solar system”.
Sweden among world leaders
Sweden’s success with Alma is not limited to delivering instruments. Swedish researchers were among the most frequent users of the telescopes last year, second only to Japan.
“Second place! That shows the strength and position of Swedish astronomical research in international terms. With the support of instrumentation, we are at one of the world's leading positions - both in terms of research and technology. That’s something to be proud of", says Victor Belitsky.
Text: Christian Löwhagen.
Photo: Oscar Mattson - GARD-Group. Receivers in the cryostat: ESO/P. Yagoubov.
, professor, and Head of unit, Department of Space, Earth and Environment, Onsala Space Observatory, Advanced receiver development (GARD), +46 31 772 18 93.