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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. ALMA is expected to provide insight on star
birth during the early Stelliferous era and detailed imaging of local star and planet
formation. ALMA is an international partnership among
Europe, the United States, Canada, Japan, South Korea, Taiwan, and Chile. Costing about US$1.4 billion, it is the most
expensive ground-based telescope in operation. 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.==Overview==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. 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. 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.===History===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). 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.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, 26 in total which were delivered to Antwerp for onward shipment to Chile.==Funding==
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. ALMA is the largest and most expensive ground-based
astronomical project, costing between US$1.4 and 1.5 billion. (However, various space astronomy projects
including Hubble Space Telescope, JWST, and several major planet probes have cost considerably
more). PartnersEuropean Southern Observatory and
the European Regional Support Centre National Science Foundation via the National
Radio Astronomy Observatory and the North American ALMA Science Center
National Research Council of Canada National Astronomical Observatory of Japan
(NAOJ) under the National Institutes of Natural Sciences (NINS)
ALMA-Taiwan at the Academia Sinica Institute of Astronomy & Astrophysics (ASIAA)
Republic of Chile==
Assembly==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, while European manufacturer Thales Alenia Space provided the other twenty-five
principal antennas (in the largest-ever European industrial contract in ground-based astronomy). The first antenna was delivered in 2008, the
last in 2011.===Transporting antennas===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. The solution chosen is to use two custom 28-wheel
self-loading heavy haulers. The vehicles were made by Scheuerle Fahrzeugfabrik
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. 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). 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. In October 2012, 43 of the 66 antennas had
been set up.==Scientific results=====
Images from initial testing===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. 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).===Planetary formation===
An image of the protoplanetary disk surrounding HL Tauri (a very young T Tauri star 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.===Event Horizon Telescope===
ALMA participated in the Event Horizon Telescope project, which produced the first direct image
of a black hole.==Global collaboration==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. Its current director since February 2018 is
Sean Dougherty.==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 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.==Project detail==At least 50 antennas of 12 m diameter located
at an elevation of 5,000 m at Llano de Chajnantor Observatory, enhanced by a compact array of
4 x 12 m and 12 x 7 m antennas (consortium currently considering to build 50 or 64 [1]
[2]) Imaging instrument in all atmospheric windows
between 350 μm and 10 mm Array configurations from approximately 150
m to 14 km Spatial resolution of 10 milliarcseconds (10−7
radians), 10 times better than the Very Large Array (VLA) and 5 times better than the Hubble
Space Telescope, but still considerably lower than the resolution achieved with optical
and infrared interferometers. The ability to image sources arcminutes to
degrees across at one arcsecond resolution Velocity resolution under 50 m/s
Faster and more flexible imaging instrument than the Very Large Array
Largest and most sensitive instrument in the world at millimeter and submillimeter wavelengths
Point source detection sensitivity 20 times better than the Very Large Array
Data reduction system will be CASA (Common Astronomy Software Applications) which is
a new software package based on AIPS++===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.==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. After 17 days an agreement was reached providing
for reduced schedules and higher pay for work done at high altitude.==Project timeline====
Videos and gallery==Videos Antenna transport Miscellaneous==
See also==Atacama Pathfinder Experiment (APEX), single
dish submillimeter telescope built on a modified ALMA prototype antenna
Atacama Submillimeter Telescope Experiment CARMA a sensitive millimeter-wave array operated
by a consortium including Caltech, University of California Berkeley, University of Illinois,
University of Maryland and University of Chicago Cosmic Background Imager a 13 element interferometer
operating in Llano de Chajnantor since 1999. IRAM 30 Meter Telescope (Pico Veleta, Spain),
the largest millimetric telescope in the world, operated by IRAM
List of astronomical observatories

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