ALMA

ALMA. The Atacama Large Millimeter/submillimeter Array is a premier international astronomical facility located on the Chajnantor Plateau in the Atacama Desert of northern Chile. It is a single telescope composed of 66 high-precision antennas working together at millimeter and submillimeter wavelengths, offering unprecedented resolution and sensitivity. This revolutionary instrument is designed to study the cold universe, probing the molecular gas and dust that constitute the building blocks of stars, planetary systems, galaxies, and life itself.

Overview

ALMA represents a transformative collaboration between Europe, North America, and East Asia in partnership with the host nation, the Republic of Chile. The facility is managed through a tripartite agreement between the European Southern Observatory (ESO), the U.S. National Science Foundation in cooperation with the National Research Council of Canada and the National Radio Astronomy Observatory (NRAO), and the National Astronomical Observatory of Japan (NAOJ) in cooperation with the Academia Sinica Institute of Astronomy and Astrophysics of Taiwan and the Korea Astronomy and Space Science Institute. Its location at an altitude of 5,000 meters above sea level was strategically chosen for its exceptionally dry atmosphere, which is transparent to the faint millimeter and submillimeter radiation that ALMA detects. This positioning places it above a significant portion of the Earth's water vapor, a major source of interference for observations at these wavelengths.

History and development

The concept for ALMA emerged from separate planning efforts in the 1990s, including the Millimeter Array (MMA) project in the United States and the Large Southern Array (LSA) concept in Europe. Following a historic agreement in 1999, these projects were merged into a single global endeavor. The ALMA Agreement was formally signed in 2003 by the international partners, and construction began shortly thereafter on the Llano de Chajnantor Observatory site. Major milestones included the production of the first prototype antenna in 2008, the arrival of the first antenna on the high site in 2009, and the beginning of early science observations in 2011. The array was inaugurated in a ceremony in March 2013, attended by the President of Chile, Sebastián Piñera, and representatives from the partner organizations, marking its transition to full operations.

Technical specifications

The array's technical heart consists of fifty 12-meter diameter antennas and an additional compact array of twelve 7-meter antennas and four 12-meter antennas, known as the Atacama Compact Array (ACA). These antennas can be repositioned across the desert plateau along 192 antenna pads, with configurations spanning from 150 meters to 16 kilometers apart, allowing astronomers to adjust the resolution of their observations. The signals from the antennas are combined using a technique called aperture synthesis, performed by a specialized supercomputer known as the ALMA correlator. This system operates at some of the highest frequencies in radio astronomy, covering bands from 84 to 950 GHz. The antennas themselves are engineering marvels, with surfaces polished to accuracies of better than 25 micrometers to precisely focus the short-wavelength light.

Scientific objectives and discoveries

ALMA's primary scientific mission is to image the local universe with angular resolution superior to that of the Hubble Space Telescope at its designed wavelengths. Key objectives include studying the formation of stars and planets in detail within dusty regions like the Orion Nebula, probing the chemistry of protoplanetary disks, and investigating the physical conditions in galaxies like the Andromeda Galaxy throughout cosmic time. Its landmark discoveries are numerous, including capturing the first detailed image of a protoplanetary disk with gaps indicative of planet formation around the star HL Tauri, mapping the complex gas dynamics in the nearby starburst galaxy the Antennae Galaxies, and detecting simple organic molecules in the distant universe. It has also provided unprecedented views of the supermassive black hole at the center of the Messier 87 galaxy, complementing the work of the Event Horizon Telescope.

Operations and collaboration

Observations with ALMA are conducted through a process of competitive proposal submission, reviewed by international panels of astronomers. The Joint ALMA Observatory (JAO), headquartered in Santiago, oversees the unified operation and execution of the observatory's scientific mission. The JAO directs the work of the ALMA Operations Support Facility (OSF) at a lower 2,900-meter altitude, where technical staff and scientists prepare for work at the high site. The scientific data is processed and archived at regional centers operated by the partners: the ALMA Regional Centre (ARC) in Europe, the North American ALMA Science Center (NAASC), and the East Asian ALMA Regional Centre. This distributed model ensures that the global astronomical community can effectively access and utilize the telescope's groundbreaking capabilities.

Category:Radio telescopes Category:Astronomical observatories in Chile Category:European Southern Observatory