ALMA - Atacama Large Millimetre/submillimetre Array

ALMA: Imaging the light from cosmic dawn

This picture of the ALMA antennas on the Chajnantor Plateau, 5000 m above sea level, was taken a few days before the start of ALMA Early Science. (Credit: ALMA (ESO/NAOJ/NRAO)/W. Garnier)

The Atacama Large Millimetre/submillimetre Array (ALMA), nearing completion in the high desert of northern Chile, is one of astronomy's most powerful telescopes, providing unprecedented imaging capabilities and sensitivity many orders of magnitude greater than anything of its kind before.

ALMA, still under construction, will be an array of 66 radio antennas that will work together as one telescope to study millimetre- and submillimetre-wavelength light from space. These wavelengths, which cross the critical boundary between infrared and microwave radiation, hold the key to understanding such processes as planet and star formation, the formation of early galaxies and galaxy clusters, and the formation of organic and other molecules in space.

An international partnership involving North America, Europe and East Asia funds and operates ALMA. The National Research Council of Canada has joined with the U.S. National Radio Astronomy Observatory to form the North American component of this project, which is the largest ground-based astronomy endeavour ever undertaken. Some funding has also been provided by the Canada Foundation for Innovation.

This view of the Antennae Galaxies combines ALMA observations with visible-light observations from the Hubble Space Telescope. Visible light – shown mainly in blue – reveals the newborn stars in the galaxies, while ALMA (red, pink and yellow) show us the clouds of dense cold gas from which new stars form. (Credit: ALMA (ESO/NAOJ/NRAO). Visible light image: the NASA/ESA Hubble Space Telescope)

Early science

Though still under construction, in 2011 ALMA surpassed all other millimetre/submillimetre-wave telescopes, and astronomers were given the opportunity to request astronomical data from the incomplete but already powerful telescope. The response was overwhelming, with nearly ten hours of observations requested for every hour available on the telescope. "Early Science" observing began at the end of September 2011.

What is millimetre-wavelength astronomy?

Astronomers learn about objects in space by studying the energy they emit. Our Sun and the other stars throughout the Universe emit visible light. But, there are other types of objects that also emit other kinds of energy, such as X-rays, infrared radiation, and radio waves. Some emit very little or no visible light, yet are strong sources of other wavelengths of electromagnetic radiation.

Much of the radiation energy in the Universe is present in the millimetre portion of the spectrum. This radiation comes from the cold dust and gas that fills interstellar and even intergalactic space. It also comes from distant galaxies and galaxy clusters that formed many billions of years ago at the edges of the known universe.

With ALMA, astronomers are gaining access to this remarkable portion of the spectrum.

Previous observatories simply did not have anywhere near the necessary sensitivity and resolution to unlock the secrets that the abundant millimetre wavelength "light" can reveal. It has taken the unparalleled power of ALMA to fully study this energy and better understand the nature of the universe.

ALMA's unique capabilities

ALMA's ability to detect remarkably faint millimetre emission and to create highly detailed images of the sources of that emission, will give it capabilities not found in any other astronomical instrument. ALMA is therefore able to observe phenomena previously out of reach to astronomers and astrophysicists. These capabilities include studying:

• The formation of galaxies (like the Milky Way) at the earliest times in cosmic history
• New planets forming around young stars in our Galaxy
• The birth of new stars in spinning clouds of gas and dust
• The evolutionary stages of aging stars as they shed their outer atmospheres on the way to becoming white dwarfs
• Interstellar clouds of gas and dust that are chemical factories forming complex molecules and even organic chemicals related to the building blocks of life.

ALMA at night (Credit: ALMA (ESO/NAOJ/NRAO), C. Padilla (NRAO/AUI/NSF))

How does ALMA work?

All of ALMA's antennas work in concert, taking quick "snap shots" or long-term exposures of astronomical objects and large portions of the sky. Cosmic millimetre waves from these objects are reflected up from the surface of each dish to the subreflector above the dish's centre. From there they are guided down into highly sensitive receivers operating at just a few degrees above Absolute Zero (-273 °C). There the signals are amplified many millions of times, digitized, and then sent along underground fibre-optic cables to a large signal processor in the control building.

This specialized computer, called a correlator - running at 16,000 million-million operations per second - combines all of the data from the antennas to make images of remarkable quality. The configuration of the antennas is variable, providing a sort of zoom capability. In its largest configuration, the image detail provided by the completed array will be comparable to that which a single radio telescope 14 km in diameter would provide.

Who uses the telescope?

Scientists from all over the world use ALMA. They compete for observing time by submitting proposals, which are judged by a group of their peers on the basis of scientific merit.

The Atacama Large Millimetre Array (ALMA) VertexRSI test antenna constructed at the site of the Very Large Array near Socorro, NM. (Credit: NRAO/AUI)

Canadian contributions

Funding for the contributions that secured Canada's place in the ALMA partnership has been provided by the National Research Council of Canada and by the Canada Foundation for Innovation. Canada provides funding in support of ALMA operations through NRC and is providing in-kind support to the North American ALMA Research Center.

The largest Canadian contribution to ALMA construction is the receivers for one of ALMA's frequency bands. The millimetre instrumentation laboratory of the NRC Herzberg Institute of Astrophysics in Victoria, BC, is one of the few facilities in the world with expertise in superconducting detector technology for millimetre waves. This technology employs tiny switches about 50 times smaller than the width of a human hair, operating at liquid Helium temperatures of -269 °C to detect and amplify the incredibly faint whispers of radiation that reach Earth from the remotest parts of the cosmos. Canada has supplied 73 receivers of unprecedented sensitivity for the 3-millimetre wavelength band - the so-called ALMA Band 3 Receivers. These receivers are of paramount importance to the project because they will be used not only for many science applications but also for final adjustment of the antenna panels and for regular calibration of the array during operations. Several Canadian companies have made significant contributions to this challenging multimillion-dollar program, including Nanowave Technologies of Etobicoke, Ontario for the construction of the detector assemblies and the cryogenic low noise amplifiers; Daniels Electronics of Victoria, B.C. for materials management and mechanical integrations; and K-Tec Industry and Prototype Equipment Design of British Columbia for providing high precision micro-machined parts.

The University of Calgary and McMaster University have received grants from the Canada Foundation for Innovation to fund Canada's share of the general site infrastructure costs and also to contribute as part of an international ALMA software development team. The data flow rate from this huge array will be exceedingly high, and Canadian programmers and astronomers at these universities will be developing highly specialized code to allow visiting astronomers to acquire and process the images provided by ALMA.

The extraordinary ALMA site

Since atmospheric water vapour absorbs millimetre waves, ALMA needed to be constructed in a very dry area, preferably at a very high altitude. Extensive tests showed that the sky above the Atacama Desert of Chile had the unsurpassed clarity and stability essential for ALMA. That is why ALMA is being built there at 5,000 metres (16,500 feet) elevation in the Chilean Andes.

Chile, as the host nation for ALMA, is participating in the project through its presence on the ALMA Board, and other ALMA committees, and by making available the superb astronomical site in the Atacama Altiplano.

View south from Cerro Chajnantor, Chile, of ALMA site (Credit: NRAO/AUI)

Timeline for ALMA

• June 1998: Phase 1 (Research and Development)
• June 1999: European/American Memorandum of Understanding
• January 2002: North American Prototype Antenna Testing at VLA Site
• July 2003: European Prototype Antenna Testing at VLA Site
• 2007: First fringes on test interferometer
• 2011: Initial scientific operation of the partial array
• 2013: Final construction of the array

ALMA Links

Links in this section lead to sites belonging to entities not subject to the Official Languages Act. Information on such a site is available in the language of the site.

Des liens dans cette section conduisent aux sites d'entités non assujetties à la Loi sur les langues officielles. L'information sur un tel site est disponible dans la langue du site.

Joint ALMA Observatory
North America - National Radio Astronomy Observatory (NRAO)
Europe - European Southern Observatory
Asia - National Astronomy Observatory of Japan

Related Information

Institutes:

• NRC Herzberg Institute of Astrophysics