A new look into the universe

Understanding our cosmic origin is a fundamental goal of astronomers across the world, one which demands highly sophisticated telescopes with a large collecting area. Located in the Chilean Atacama desert, the Atacama Large Millimetre/submillimetre Array (ALMA) Observatory will allow astronomers to study distant phenomena, says Dr Wolfgang Wild, European ALMA Project Manager at the European Southern Observatory (ESO)..

The field of millimetre and sub-millimetre astronomy is relatively young. The first millimetre observation was made around 1970, and since then technical improvements have generated exciting scientific data and new insights into the universe, improvements which the ALMA Observatory aims to build on further. “The goal is to build a state-of-the art observatory to study light from some of the coldest objects in the universe. At optical wavelengths we see hot objects, such as our sun, but at longer wavelengths we see cold objects, like those gas clouds where new stars form,” explains Dr Wolfgang Wild. Currently under construction, the ALMA observatory will cover the wavelength range between 0.3 and 10 millimetres, equivalent to a frequency range from 30 GHz to 950 GHz, and will be used to study several areas of astronomy. “ALMA is actually being built for a wide range of scientific studies,” says Dr Wild. “The Observatory is not intended only for experts in millimetre astronomy, but for all astronomers. This is a different approach to many other instruments; right from the design phase we’ve built ALMA so that any professional astronomer can use it, even if they are not an expert in that specific field. This means that the user interface and access to the telescope has to be straightforward and simple.”

Origins of ALMA

The origins of ALMA lie in a desire shared by European, American and Asian scientists to study the formation and development of galaxies, stars and planetary systems in greater detail. Comprised of 66 high-precision radio telescopes, also called antennas, the ALMA Observatory will allow researchers to look back in time and study how the first galaxies formed. “At the moment we are able to observe galaxies, but we don’t really know why they have the form and variety that we see. ALMA will enable us to study the processes of galaxy, star and planet formation; in terms of resolution we also hope to see planetary systems in the first stages of formation, which is very important to understanding our cosmic origins,” outlines Dr Wild. The observatory can also be used to study the universe’s rich chemistry, as well as numerous other phenomena. “By ensuring that ALMA covers a wide range of millimetre and submillimetre wavelengths, we can study these phenomena. For example we can study molecules by observing what’s called their rotational lines – they rotate and when they change the state of rotation they emit light, and that light is in the frequency range we can observe with ALMA. So we can basically see the fingerprints of molecules,” explains Dr Wild. “We can also study gas clouds by their thermal emission. Any physical body that has a certain temperature radiates a characteristic spectrum.”

Detecting these kinds of signals requires highly sophisticated technologies, including antennas, transporters, receivers and digital electronics. ALMA will have 66 antennas which can be moved between almost 200 different positions and an overall collecting area of approximately 6,500 square metres, which is needed to detect weak signals. “The more collecting area we have the more light we can detect, which means we can see fainter, weaker signals in the universe. If we can see fainter, weaker signals we can look further back in time – the further back you look generally the weaker the signal. The other reason we need many antennas is for image quality. The more image points we have the more information we can gather about a certain object and the better we can reconstruct its initial structure,” he explains. Specially designed detectors employing state-of-the art superconducting elements are used to ensure high levels of sensitivity. Another key European technological achievement is the antenna transporters. “These are dedicated, custom-designed vehicles to transport these 120 ton antennas at 5,000 metres and position them with a very high level of precision,” Dr. Wild says.

Atacama desert

It was also important to locate the observatory in an area where atmospheric interference would be at a minimum. “Millimetre waves are very much attenuated by water vapour in the atmosphere. So we need to go to a location where there’s minimal water vapour in the atmosphere, and that’s usually the case in deserts,” says Dr Wild. “We also need a site with low oxygen and ozone levels, because these also attenuate astronomical signals, and therefore a site at high altitude is mandatory. In addition, the ALMA site should have a relatively flat area over a diameter of about 16 kms where we could place the array of 66 antennas. Finally it should also be in the southern hemisphere, where the sky is very rich for astronomical observations.”

The high, dry, flat Chajnantor plateau in Northern Chile’s Atacama desert represents the ideal location in terms of all these requirements. The telescopes are located at an altitude of 5,000 metres, from where astronomers can look deep into space. “We can see the centre of our own galaxy from this location, which we cannot do from the northern hemisphere. We can also see the Magellanic Clouds, two of the closest neighbouring galaxies to our own,” enthuses Dr Wild. However, there are some significant technical challenges involved in building an observatory at such a high altitude. “These are fairly big, parabolic antennas, and they need to have a precision level of about 25 microns (about half the diameter of a human hair), over the whole surface. That’s technically very challenging,” stresses Dr Wild. “We also need to position these antennas very precisely. We have almost 200 antenna foundations on-site, and the antennas can be re-located – so they can be picked up by our heavy-duty custom made transporters and then put down on other well defined locations, to get a configuration optimized for certain types of astronomical observations. This positioning is done with very high precision by a specially designed laser alignment system. Then we also need very dedicated radio receivers. We use super-conducting detector elements – that means we need to have cooling machines integrated in each antenna to produce these very low temperatures – 2.5 Kelvin, or -271o Celsius. There’s not much industrial capability in the area of these receivers, so we work with European, American and Asian research institutes and universities that develop this kind of technology.”

The Observatory itself is still in the construction phase and activity is ongoing in the Atacama desert. The array is expected to be completed by about 2013, but with the Observatory having already generated intense interest from astronomers around the world, there are plans to make part of the instrument available in the second half of 2011. “We plan to provide 16 antennas for scientific observations, with certain limitations in terms of resolution, observing modes and time,” says Dr. Wild. These resources are intended for astronomers across the world, who will be free to submit research proposals and requests to observe a specific wavelength; however, Dr Wild says this is a competitive process. “Usually observatories do not have enough time to honour all requests, demand usually outstrips supply by up to a factor of five. Proposals will be assessed technically and are ranked according to scientific quality and value, and only the very best proposals will get observing time,” he stresses. “We will apply the standard process followed by astronomical observatories open to the scientific community. We also apply this process to our other optical observatories in Chile, where the best scientists from the community get together in what’s called the Programme Committee, and they evaluate and judge the proposals of the community. The main evaluation criterion is scientific excellence.”

When ALMA is completed, researchers will be able to use all 66 antennas to observe a particular wavelength, such as for very faint signals which require a high level of sensitivity, while it will also be possible to split up the array of antennas into so-called sub-arrays. In both cases the data is preserved and collated within the observatory. “Each antenna collects the data, which is then sent via glass fibre to a central data acquisition system,” says Dr Wild. A specially designed correlator, a kind of supercomputer, combines the signals, from which data is typically processed further before being transferred to the astronomers. “All data is archived, so whatever is observed with ALMA will be kept in a huge computer archive, and after one year it will be made available to the global science community,” he continues. This is an important consideration given the complexity of modern astronomy research, and data from ALMA will be integrated with information gathered by other projects.

“The integration of observations from across the electromagnetic spectrum is essential to a proper understanding of astronomical objects,” says Dr Hans Rykaczewski, another key figure within the project. “ALMA will be used together with other frontline observatories, both space and ground-based. The synergies with Herschel, a European Space Agency telescope operating since May 2009 in space, are particularly important, because its wavelength range overlaps partly with ALMA’s. These two observatories can therefore provide complementary information, with Herschel observing parts of the spectrum which do not penetrate the earth’s atmosphere, while ALMA has the advantage of a much higher spatial resolution.”

This means ALMA can follow-up on targets detected by Herschel, allowing researchers to look in-depth at some of the most fundamental questions in astronomy. “In a sense by looking far out we observe the past in the Universe and in combination with accurate scientific models, we would like to understand the further evolution of the Universe. What’s the future of the universe? How is it going to develop? Is there other life out there in the universe? Are there other planets out there similar to earth, with water, with life as we know it? This touches on the deepest questions of human existence.” says Dr Wild.

For more information, please visit the ESO website.

(Image credit: APLF/ESO)

Published: Wednesday, 2nd March 2011