ALMA
The Atacama Large Millimeter Array
ALMA is a unique astronomical observatory located on a high plateau in the Chilean Andes. It was built by a large international partnership with participation from Europe, Chile, the U.S, Canada, Japan, Taiwan and South Korea. Combining the signals of the 66 parabolic antennas in a technique called interferometry, ALMA can make incredibly sharp and sensitive observations. Thanks to the unique location, it can do so at millimeter and sub-millimeter wavelengths, which allows astronomers to study the chemical composition of clouds from which stars and planets form, as well as distant galaxies in the early universe.
Infrastructure and User Services
The ALMA observatory was built to conduct interferometric observations in the millimeter and sub-millimeter wavelength range (frequencies of 31 to 950 GHz). As these wavelengths are absorbed by moisture in the earth’s atmosphere, the observatory has been built on one of the highest and driest locations on the planet: The Chajnantor plateau in the Chilean Andes. ALMA employs 66 telescope or antennas. Each antenna consists of a parabolic primary reflector, either 7 or 12 meters in diameter, and secondary reflector that focusses the radiation into a cryostat, housing the receivers. The antennas can be repositioned to create different configurations with longer or shorter baselines for interferometry. The ALMA observable wavelength range has been divided into 10 frequency bands. Dedicated sets of receivers have been built for each frequency band, with each antenna having 10 receivers mounted in a cryostat. The antennas use superconducting elements and operate at temperatures down to 4K. Using fibre-optic cables, the received signals are sent to a central location where a massive supercomputer, the correlator, combines the signals into images.
The ALMA observatory has been developed by an international collaboration, with partner institutes from Europe, North America and South-East Asia. The observatory started operating in 2011. Responding to annual calls, astronomers from participating nations can submit proposals for observing time. Proposals are selected in a peer-reviewed process. ALMA provides the users with calibrated data. ALMA observers are supported by ALMA Regional Centers (ARCs); a node of the European ARC network is hosted by Leiden University (Allegro).
Examples/description of the type of research
ALMA provides observations in a unique wavelength range, enabling it to:
• Study the first stars and galaxies that emerged from the cosmic “dark ages”, billions of years ago. These objects lie at huge distances, with most of their emissions stretched out to millimeter and submillimeter wavelengths, due to the expansion of the Universe.
• Within the nearby Universe, ALMA provides an unprecedented ability to study the processes of star and galaxy formation. Unimpeded by the dust that obscures visible light observations, ALMA can reveal the details of young, still-forming stars and show young planets still in the process of development.
• ALMA is allowing scientists to carry out research on the complex chemistry of the giant cosmic clouds of gas and dust that spawn stars and planetary systems.
How to access the infrastructure?
1 Astronomers from the participating countries and institutes can submit observing proposals in response to an annual call. Proposals are selected based on peer review.
2 Partners contribute some of their observing time towards an ‘open call’ to which all astronomers can submit proposals, regardless of affiliation. Proposals are again selected based on peer review.
3 Open access: Observation data becomes available to all interested researchers after the end of the proprietary period, typically one year.