Atacama Large Millimeter Array

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Atacama Large Millimeter Array
ALMA Antennas on Chajnantor.jpg
Alternative namesALMA Blue pencil.svg
Observatory Llano de Chajnantor Observatory   Blue pencil.svg
Location(s) Atacama Desert, Antofagasta Region, Chile Blue pencil.svg
Coordinates 23°01′09″S67°45′12″W / 23.0193°S 67.7532°W / -23.0193; -67.7532 Coordinates: 23°01′09″S67°45′12″W / 23.0193°S 67.7532°W / -23.0193; -67.7532 Blue pencil.svg
Organization European Southern Observatory
National Institutes of Natural Sciences
National Science Foundation   Blue pencil.svg
Altitude5,058.7 m (16,597 ft) Blue pencil.svg
Telescope style Radio telescope
radio interferometer   Blue pencil.svg
Website Blue pencil.svg
Relief Map of Chile.jpg
Red pog.svg
Location of Atacama Large Millimeter Array

The Atacama Large Millimeter/submillimeter Array (ALMA) is an astronomical interferometer of 66 radio telescopes in the Atacama Desert of northern Chile, which observe electromagnetic radiation at millimeter and submillimeter wavelengths. The array has been constructed on the 5,000 m (16,000 ft) elevation Chajnantor plateau - near the Llano de Chajnantor Observatory and the Atacama Pathfinder Experiment. This location was chosen for its high elevation and low humidity, factors which are crucial to reduce noise and decrease signal attenuation due to Earth's atmosphere. [1] ALMA is expected to provide insight on star birth during the early Stelliferous era and detailed imaging of local star and planet formation.

Astronomical interferometer array of separate telescopes, mirror segments, or radio telescope antennas that work together as a single telescope

An astronomical interferometer is an array of separate telescopes, mirror segments, or radio telescope antennas that work together as a single telescope to provide higher resolution images of astronomical objects such as stars, nebulas and galaxies by means of interferometry. The advantage of this technique is that it can theoretically produce images with the angular resolution of a huge telescope with an aperture equal to the separation between the component telescopes. The main drawback is that it does not collect as much light as the complete instrument's mirror. Thus it is mainly useful for fine resolution of more luminous astronomical objects, such as close binary stars. Another drawback is that the maximum angular size of a detectable emission source is limited by the minimum gap between detectors in the collector array.

Radio telescope form of directional radio antenna used in radio astronomy

A radio telescope is a specialized antenna and radio receiver used to receive radio waves from astronomical radio sources in the sky in radio astronomy. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency portion of the electromagnetic spectrum emitted by astronomical objects, just as optical telescopes are the main observing instrument used in traditional optical astronomy which studies the light wave portion of the spectrum coming from astronomical objects. Radio telescopes are typically large parabolic ("dish") antennas similar to those employed in tracking and communicating with satellites and space probes. They may be used singly or linked together electronically in an array. Unlike optical telescopes, radio telescopes can be used in the daytime as well as at night. Since astronomical radio sources such as planets, stars, nebulas and galaxies are very far away, the radio waves coming from them are extremely weak, so radio telescopes require very large antennas to collect enough radio energy to study them, and extremely sensitive receiving equipment. Radio observatories are preferentially located far from major centers of population to avoid electromagnetic interference (EMI) from radio, television, radar, motor vehicles, and other manmade electronic devices.

Atacama Desert desert in South America

The Atacama Desert is a desert plateau in South America covering a 1000-km (600-mi) strip of land on the Pacific coast, west of the Andes mountains. The Atacama desert is one of the driest places in the world, as well as the only true desert to receive less precipitation than the polar deserts. According to estimates, the Atacama Desert occupies 105,000 km2 (41,000 sq mi), or 128,000 km2 (49,000 sq mi) if the barren lower slopes of the Andes are included. Most of the desert is composed of stony terrain, salt lakes (salares), sand, and felsic lava that flows towards the Andes.


ALMA is an international partnership among Europe, the United States, Canada, Japan, South Korea, Taiwan, and Chile. [2] Costing about US$1.4 billion, it is the most expensive ground-based telescope in operation. [3] [4] ALMA began scientific observations in the second half of 2011 and the first images were released to the press on 3 October 2011. The array has been fully operational since March 2013. [5] [6]

Europe Continent in the Northern Hemisphere and mostly in the Eastern Hemisphere

Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west and the Mediterranean Sea to the south. It comprises the westernmost part of Eurasia.

United States federal republic in North America

The United States of America (USA), commonly known as the United States or America, is a country composed of 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is slightly smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U.S. is the third most populous country. The capital is Washington, D.C., and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico. The State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean. The U.S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The extremely diverse geography, climate, and wildlife of the United States make it one of the world's 17 megadiverse countries.

Canada Country in North America

Canada is a country in the northern part of North America. Its ten provinces and three territories extend from the Atlantic to the Pacific and northward into the Arctic Ocean, covering 9.98 million square kilometres, making it the world's second-largest country by total area. Canada's southern border with the United States is the world's longest bi-national land border. Its capital is Ottawa, and its three largest metropolitan areas are Toronto, Montreal, and Vancouver. As a whole, Canada is sparsely populated, the majority of its land area being dominated by forest and tundra. Consequently, its population is highly urbanized, with over 80 percent of its inhabitants concentrated in large and medium-sized cities, many near the southern border. Canada's climate varies widely across its vast area, ranging from arctic weather in the north, to hot summers in the southern regions, with four distinct seasons.


ALMA first fringes at Chajnantor.jpg
The first two ALMA antennas linked together as an interferometer
Three ALMA antennas linked together as an interferometer for the first time
ALMA Prototype-Antennas at the ALMA Test Facility.jpg
ALMA prototype-antennas at the ALMA test facility
The moon high above Cerro Chajnantor at sunset.jpg
Cerro Chascon at sunset
Lights glowing on the ALMA correlator.jpg
The ALMA correlator

The initial ALMA array is composed of 66 high-precision antennas, and operates at wavelengths of 9.6 to 0.3 millimeters (31 to 1000 GHz). The array has much higher sensitivity and higher resolution than earlier submillimeter telescopes such as the single-dish James Clerk Maxwell Telescope or existing interferometer networks such as the Submillimeter Array or the Institut de Radio Astronomie Millimétrique (IRAM) Plateau de Bure facility.

Wavelength spatial period of the wave—the distance over which the waves shape repeats, and thus the inverse of the spatial frequency

In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is thus the inverse of the spatial frequency. Wavelength is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings and is a characteristic of both traveling waves and standing waves, as well as other spatial wave patterns. Wavelength is commonly designated by the Greek letter lambda (λ). The term wavelength is also sometimes applied to modulated waves, and to the sinusoidal envelopes of modulated waves or waves formed by interference of several sinusoids.

James Clerk Maxwell Telescope radio telescope

The James Clerk Maxwell Telescope (JCMT) is a submillimetre-wavelength telescope at Mauna Kea Observatory in Hawaii. The telescope is near the summit of Mauna Kea at 13,425 feet (4,092 m). Its primary mirror is 15 metres across: it is the largest single-dish telescope that operates in submillimetre wavelengths of the electromagnetic spectrum. Scientists use it to study the Solar System, interstellar dust and gas, and distant galaxies.

Submillimeter Array Array of radio telescopes in Hawaii

The Submillimeter Array (SMA) consists of eight 6-meter (20 ft) diameter radio telescopes arranged as an interferometer for submillimeter wavelength observations. It is the first purpose-built submillimeter interferometer, constructed after successful interferometry experiments using the pre-existing 15-meter (49 ft) James Clerk Maxwell Telescope and 10.4-meter (34.1 ft) Caltech Submillimeter Observatory as an interferometer. All three of these observatories are located at Mauna Kea Observatory on Mauna Kea, Hawaii, and can be operated together as a ten element interferometer in the 230 and 345 GHz bands. The baseline lengths presently in use range from 16 to 508 meters, and up to 783 meters (2,569 ft) for eSMA operations. The radio frequencies accessible to this telescope range from 180–418 gigahertz (1.666–0.717 mm) which includes rotational transitions of dozens of molecular species as well as continuum emission from interstellar dust grains. Although the array is capable of operating both day and night, most of the observations take place at nighttime when the atmospheric phase stability is best.

The antennas can be moved across the desert plateau over distances from 150 m to 16 km, which will give ALMA a powerful variable "zoom", similar in its concept to that employed at the centimetre-wavelength Very Large Array (VLA) site in New Mexico, United States.

Very Large Array radio astronomy observatory located on the Plains of San Agustin

The Karl G. Jansky Very Large Array (VLA) is a centimeter-wavelength radio astronomy observatory located in central New Mexico on the Plains of San Agustin, between the towns of Magdalena and Datil, ~40 miles (64 km) west of Socorro. The VLA comprises twenty-seven 25-meter radio telescopes deployed in a Y-shaped array and all the equipment, instrumentation, and computing power to function as an interferometer. Each of the massive telescopes is mounted on double parallel railroad tracks, so the radius and density of the array can be transformed to adjust the balance between its angular resolution and its surface brightness sensitivity. Astronomers using the VLA have made key observations of black holes and protoplanetary disks around young stars, discovered magnetic filaments and traced complex gas motions at the Milky Way's center, probed the Universe's cosmological parameters, and provided new knowledge about the physical mechanisms that produce radio emission.

The high sensitivity is mainly achieved through the large numbers of antenna dishes that will make up the array.

The telescopes were provided by the European, North American and East Asian partners of ALMA. The American and European partners each provided twenty-five 12-meter diameter antennas, that compose the main array. The participating East Asian countries are contributing 16 antennas (four 12-meter diameter and twelve 7-meter diameter antennas) in the form of the Atacama Compact Array (ACA), which is part of the enhanced ALMA.

By using smaller antennas than the main ALMA array, larger fields of view can be imaged at a given frequency using ACA. Placing the antennas closer together enables the imaging of sources of larger angular extent. The ACA works together with the main array in order to enhance the latter's wide-field imaging capability.


On 4 March 2011, ten antennas are installed at Chajnantor. Ten ALMA Antennas Chajnantor.jpg
On 4 March 2011, ten antennas are installed at Chajnantor.

ALMA has its conceptual roots in three astronomical projects — the Millimeter Array (MMA) of the United States, the Large Southern Array (LSA) of Europe, and the Large Millimeter Array (LMA) of Japan.

The first step toward the creation of what would become ALMA came in 1997, when the National Radio Astronomy Observatory (NRAO) and the European Southern Observatory (ESO) agreed to pursue a common project that merged the MMA and LSA. The merged array combined the sensitivity of the LSA with the frequency coverage and superior site of the MMA. ESO and NRAO worked together in technical, science, and management groups to define and organize a joint project between the two observatories with participation by Canada and Spain (the latter became a member of ESO later).

National Radio Astronomy Observatory

The National Radio Astronomy Observatory (NRAO) is a Federally Funded Research and Development Center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc for the purpose of radio astronomy. NRAO designs, builds, and operates its own high sensitivity radio telescopes for use by scientists around the world.

European Southern Observatory intergovernmental research organization for ground-based astronomy

The European Southern Observatory (ESO), formally the European Organisation for Astronomical Research in the Southern Hemisphere, is a 16-nation intergovernmental research organization for ground-based astronomy. Created in 1962, ESO has provided astronomers with state-of-the-art research facilities and access to the southern sky. The organisation employs about 730 staff members and receives annual member state contributions of approximately €162 million. Its observatories are located in northern Chile.

A series of resolutions and agreements led to the choice of "Atacama Large Millimeter Array", or ALMA, as the name of the new array in March 1999 and the signing of the ALMA Agreement on 25 February 2003, between the North American and European parties. ("Alma" means "soul" in Spanish and "learned" or "knowledgeable" in Arabic.) Following mutual discussions over several years, the ALMA Project received a proposal from the National Astronomical Observatory of Japan (NAOJ) whereby Japan would provide the ACA (Atacama Compact Array) and three additional receiver bands for the large array, to form Enhanced ALMA. Further discussions between ALMA and NAOJ led to the signing of a high-level agreement on 14 September 2004 that makes Japan an official participant in Enhanced ALMA, to be known as the Atacama Large Millimeter/submillimeter Array. A groundbreaking ceremony was held on November 6, 2003 and the ALMA logo was unveiled. [7]

National Astronomical Observatory of Japan observatory

The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations - the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

During an early stage of the planning of ALMA, it was decided to employ ALMA antennas designed and constructed by known companies in North America, Europe, and Japan, rather than using one single design. This was mainly for political reasons. Although very different approaches have been chosen by the providers, each of the antenna designs appears to be able to meet ALMA's stringent requirements. The components designed and manufactured across Europe were transported by specialist aerospace and astrospace logistics company Route To Space Alliance, [8] 26 in total which were delivered to Antwerp for onward shipment to Chile.


ALMA was initially a 50-50 collaboration between the National Radio Astronomy Observatory and European Southern Observatory (ESO) and later extended with the help of the other Japanese, Taiwanese, and Chilean partners. [9] ALMA is the largest and most expensive ground-based astronomical project, costing between US$1.4 and 1.5 billion. [3] [10] (However, various space astronomy projects including Hubble Space Telescope, JWST, and several major planet probes have cost considerably more).



Finished antenna. Observatorio espacial ALMA, Atacama, Chile, 2016-02-06, DD 05.JPG
Finished antenna.

The complex was built primarily by European, U.S., Japanese, and Canadian companies and universities. Three prototype antennas have undergone evaluation at the Very Large Array since 2002.

General Dynamics C4 Systems and its SATCOM Technologies division was contracted by Associated Universities, Inc. to provide twenty-five of the 12 m antennas, [11] while European manufacturer Thales Alenia Space provided the other twenty-five principal antennas [12] (in the largest-ever European industrial contract in ground-based astronomy). The first antenna was delivered in 2008, the last in 2011.

Transporting antennas

Garage of the transporters. Observatorio espacial ALMA, Atacama, Chile, 2016-02-06, DD 15.JPG
Garage of the transporters.

Transporting the 115  tonne antennas from the Operations Support Facility at 2900 m altitude to the site at 5000 m, or moving antennas around the site to change the array size, presents enormous challenges; as portrayed in the television documentary Monster Moves: Mountain Mission. [13] The solution chosen is to use two custom 28-wheel self-loading heavy haulers. The vehicles were made by Scheuerle Fahrzeugfabrik  [ de ] [14] in Germany and are 10 m wide, 20 m long and 6 m high, weighing 130 tonnes. They are powered by twin turbocharged 500 kW Diesel engines.

The transporters, which feature a driver's seat designed to accommodate an oxygen tank to aid breathing the thin high-altitude air, place the antennas precisely on the pads. The first vehicle was completed and tested in July 2007. [15] Both transporters were delivered to the ALMA Operations Support Facility (OSF) in Chile on 15 February 2008.

On 7 July 2008, an ALMA transporter moved an antenna for the first time, from inside the antenna assembly building (Site Erection Facility) to a pad outside the building for testing (holographic surface measurements). [16]

ALMA transporter known as Otto. ALMA transporter known as Otto.jpg
ALMA transporter known as Otto.

During Autumn 2009, the first three antennas were transported one-by-one to the Array Operations Site. At the end of 2009, a team of ALMA astronomers and engineers successfully linked three antennas at the 5,000-metre (16,000 ft) elevation observing site thus finishing the first stage of assembly and integration of the fledgling array. Linking three antennas allows corrections of errors that can arise when only two antennas are used, thus paving the way for precise, high-resolution imaging. With this key step, commissioning of the instrument began 22 January 2010.

On 28 July 2011, the first European antenna for ALMA arrived at the Chajnantor plateau, 5,000 meters above sea level, to join 15 antennas already in place from the other international partners. This was the number of antennas specified for ALMA to begin its first science observations, and was therefore an important milestone for the project. [18] In October 2012, 43 of the 66 antennas had been set up.

Scientific results

Images from initial testing

Antennae Galaxies composite of ALMA and Hubble observations Antennae Galaxies composite of ALMA and Hubble observations.jpg
Antennae Galaxies composite of ALMA and Hubble observations
HL Tauri protoplanetary disk. HL Tau protoplanetary disk.jpg
HL Tauri protoplanetary disk.

By the summer of 2011, sufficient telescopes were operational during the extensive program of testing prior to the Early Science phase for the first images to be captured. [20] These early images give a first glimpse of the potential of the new array that will produce much better quality images in the future as the scale of the array continues to increase.

The target of the observation was a pair of colliding galaxies with dramatically distorted shapes, known as the Antennae Galaxies. Although ALMA did not observe the entire galaxy merger, the result is the best submillimeter-wavelength image ever made of the Antennae Galaxies, showing the clouds of dense cold gas from which new stars form, which cannot be seen using visible light.

Comet studies

On 11 August 2014, astronomers released studies, using the Atacama Large Millimeter/submillimeter Array (ALMA) for the first time, that detailed the distribution of HCN, HNC, H2CO, and dust inside the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON). [21] [22]

Planetary formation

An image of the protoplanetary disk surrounding HL Tauri (a very young T Tauri star [23] in the constellation Taurus) was made public in 2014, showing a series of concentric bright rings separated by gaps, indicating protoplanet formation. As of 2014, most theories did not expect planetary formation in such a young (100,000-1,000,000-year-old) system, so the new data spurred renewed theories of protoplanetary development. One theory suggests that the faster accretion rate might be due to the complex magnetic field of the protoplanetary disk. [24]

Global collaboration

The future ALMA array on Chajnantor (artist's rendering) The future ALMA array on Chajnantor.jpg
The future ALMA array on Chajnantor (artist's rendering)

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Southern Observatory (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences of Japan (NINS) in cooperation with the Academia Sinica (AS) in Taiwan. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA. [25] Its director is Pierre Cox.

ALMA regional centre (ARC)

The ALMA regional centre (ARC) has been designed as an interface between user communities of the major contributors of the ALMA project and the JAO. Activates for operating the ARC have also divided into the three main regions involved (Europe, North America and East Asia). The European ARC (led by ESO) has been further subdivided into ARC-nodes [26] located across Europe in Bonn-Bochum-Cologne, Bologna, Ondřejov, Onsala, IRAM (Grenoble), Leiden and JBCA (Manchester).

The core purpose of the ARC is to assist the user community with the preparation of observing proposals, ensure observing programs meet their scientific goals efficiently, run a help-desk for submitting proposals and observing programs, delivering the data to principal investigators, maintenance of the ALMA data archive, assistance with the calibration of data and providing user feedback. [27]

Project detail

A starry night at the ALMA site. A Starry Night at ALMA.jpg
A starry night at the ALMA site.
2012 ALMA Video Compilation Released Still from 2012 ALMA Video Compilation.jpg
2012 ALMA Video Compilation Released

Atacama Compact Array

The Atacama Compact Array The Atacama Compact Array.jpg
The Atacama Compact Array

The Atacama Compact Array, ACA, is a subset of 16 closely separated antennas that will greatly improve ALMA's ability to study celestial objects with a large angular size, such as molecular clouds and nearby galaxies. The antennas forming the Atacama Compact Array, four 12-meter antennas and twelve 7-meter antennas, were produced and delivered by Japan. In 2013, the Atacama Compact Array was named the Morita Array after Professor Koh-ichiro Morita, a member of the Japanese ALMA team and designer of the ACA, who died on 7 May 2012 in Santiago. [29]

Work stoppage

In August 2013, workers at the telescope went on strike to demand better pay and working conditions. This is one of the first strikes to affect an astronomical observatory. The work stoppage began after the observatory failed to reach an agreement with the workers' union. [30] [31] [32] [33] After 17 days an agreement was reached providing for reduced schedules and higher pay for work done at high altitude. [34] [35]

Project timeline

The final ALMA antenna. The final ALMA antenna.jpg
The final ALMA antenna.
1995ESO/NRAO/NAOJ joint site testing with Chile.
May 1998Start of phase 1 (design & development).
June 1999European/U.S. memorandum of understanding for design & development.
February 2003Final European / North American agreement, with 50% of funding from ESO, and 50% of funding shared between USA and Canada.
April 2003Testing of first prototype antenna begins at the ALMA Test Facility (ATF) site in Socorro, New Mexico.
November 2003Groundbreaking ceremony at ALMA site.
September 2004European, North American & Japanese draft agreement, with Japan providing new extensions to ALMA.
October 2004Opening of Joint ALMA office, Santiago, Chile.
September 2005Taiwan joins the ALMA Project through Japan.
July 2006European, North American & Japanese amend agreement on the Enhanced ALMA.
April 2007Arrival of first antenna in Chile.
February 2008Arrival of the two ALMA transporters in Chile.
July 2008First antenna movement with a transporter.
December 2008Acceptance of the first ALMA antenna.
May 2009First interferometry with two antennas at the Operations Support Facility (OSF).
September 2009First move of an ALMA antenna to Chajnantor.
November 2009Phase closure with three antennas at Chajnantor.
2010Call for shared-risk Early Science proposals.
September 2011Start of Early Science Cycle 0. Sixteen 12-m antennas in the 12-m array.
February 2012First paper published with ALMA data [37]
January 2013Start of Early Science Cycle 1. Thirty-two 12-m antennas in the 12-m array.
March 13 2013ALMA Inauguration.
June 2014Start of Early Science Cycle 2. Thirty-four 12-m antennas in the 12-m array, nine 7-m antennas in the 7-m array, and two 12-m antennas in the TP array.
June 2018ALMA 1000th published paper [38]

See also

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The Large Latin American Millimeter Array (LLAMA) is a single-dish 12 m Nasmyth optics antenna with VLBI capability which is under construction in the Puna de Atacama desert in the Province of Salta, Argentina. The primary mirror accuracy will allow observation from 40 GHz up to 900 GHz. It is also planned to install a bolometer camera at millimeter wavelengths. After installation it will be able to join other similar instruments to perform Very Large Base Line Interferometry or to work in standalone mode. Financial support is provided by the Argentinian government through its Science Ministry, and from Brazil through a FAPESP grant. The total cost of construction, around US$20 million, and operation as well as the telescope time use will be shared equally by the two countries. Construction planning started in July 2014 after the formal signature of an agreement between the main institutions involved.


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