The Giant Magellan Telescope (GMT) is a ground-based,

extremely large telescope The Extremely Large Telescope (ELT) is an astronomical observatory under construction. When completed, it will be the world's largest optical and near-infrared extremely large telescope. Part of the European Southern Observatory (ESO) agency, ...

currently under construction at

Las Campanas Observatory Las Campanas Observatory (LCO) is an astronomy, astronomical observatory managed by the Carnegie Institution for Science (CIS). Located in Chile's Atacama Region, it sits about northeast of the city of La Serena, Chile, La Serena. The LCO's telesc ...

in Chile's

Atacama Desert The Atacama Desert () is a desert plateau located on the Pacific Ocean, Pacific coast of South America, in the north of Chile. Stretching over a strip of land west of the Andes Mountains, it covers an area of , which increases to if the barre ...

. With a primary mirror diameter of 25.4 meters, it is expected to be the largest Gregorian telescope ever built, observing in optical and mid-infrared wavelengths (320–25,000 nm). Commissioning of the telescope is anticipated in the early 2030s. The GMT will feature seven of the world's largest mirrors, collectively providing a light-collecting area of 368 square meters. It is expected to have a resolving power approximately 10 times greater than the

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

and four times greater than the

James Webb Space Telescope The James Webb Space Telescope (JWST) is a space telescope designed to conduct infrared astronomy. As the largest telescope in space, it is equipped with high-resolution and high-sensitivity instruments, allowing it to view objects too old, Lis ...

. However, it will not be able to observe in the same infrared frequencies as space-based telescopes. The GMT will be used to explore a wide range of astrophysical phenomena, including the search for signs of life on

exoplanets An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first detec ...

and the study of the cosmic origins of chemical elements. The casting of the GMT's primary mirrors began in 2005, and construction at the site started in 2015. By 2023, all seven primary mirrors had been cast, the first of seven adaptive secondary mirrors was under construction, and the telescope mount was in the manufacturing stage. Other subsystems of the telescope were in the final stages of design. The project, with an estimated cost of USD $2 billion, is being developed by the GMTO Corporation, a consortium of research institutions from seven countries: Australia, Brazil, Chile, Israel, South Korea, Taiwan, and the United States.

Site

The telescope is located at Las Campanas Observatory, which is also home to the

Magellan Telescopes The Magellan Telescopes are a pair of optical telescopes located at Las Campanas Observatory in Chile. The two telescopes are named after the astronomer Walter Baade and the philanthropist Landon T. Clay. First light for the telescopes was on ...

. The observatory is situated approximately north-northeast of La Serena, and south of

Copiapó Copiapó () is a List of cities in Chile, city and communes of Chile, commune in northern Chile, located about 65 kilometers east of the coastal List of towns in Chile, town of Caldera, Chile, Caldera. Founded on December 8, 1744, it is the capi ...

, at an altitude of . The site has been owned by the

Carnegie Institution for Science The Carnegie Institution for Science, also known as Carnegie Science and the Carnegie Institution of Washington, is an organization established to fund and perform scientific research in the United States. This institution is headquartered in W ...

since 1960. Las Campanas was selected as the location for the GMT due to its exceptional

astronomical seeing In astronomy, seeing is the degradation of the real image, image of an astronomical object due to turbulence in the atmosphere of Earth that may become visible as blurring, twinkling or variable Distortion (optics), distortion. The origin of this ...

conditions and clear weather throughout much of the year. The sparse population in the surrounding Atacama Desert, combined with favorable geographical conditions, ensures minimal

atmospheric An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosphere ...

and

light pollution Light pollution is the presence of any unwanted, inappropriate, or excessive artificial Visible spectrum, lighting. In a descriptive sense, the term ''light pollution'' refers to the effects of any poorly implemented lighting sources, during the ...

. This makes the area one of the best locations on Earth for long-term astronomical observation. The observatory's southern hemisphere location also provides access to significant astronomical targets, including the galactic center of the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

, the nearest

supermassive black hole A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions, of times the mass of the Sun (). Black holes are a class of astronomical ...

(

Sagittarius A* Sagittarius A*, abbreviated as Sgr A* ( ), is the supermassive black hole at the Galactic Center of the Milky Way. Viewed from Earth, it is located near the border of the constellations Sagittarius and Scorpius, about 5.6° south o ...

), the nearest star to the Sun (

Proxima Centauri Proxima Centauri is the nearest star to Earth after the Sun, located 4.25 light-years away in the southern constellation of Centaurus. This object was discovered in 1915 by Robert T. A. Innes, Robert Innes. It is a small, low-mass st ...

), the

Magellanic Clouds The Magellanic Clouds (''Magellanic system'' or ''Nubeculae Magellani'') are two irregular dwarf galaxies in the southern celestial hemisphere. Orbiting the Milky Way galaxy, these satellite galaxies are members of the Local Group. Because both ...

, and numerous nearby galaxies and exoplanets.

Design and status

The Giant Magellan Telescope's Gregorian design will produce the highest possible image resolution of the universe over the widest field of view with only two light collecting surfaces, making it the most optically proficient of all extremely large telescopes in the 30-meter class.

Table: Performance Specifications

Site preparation began with the first blast to level the mountain peak on March 23, 2012. In November 2015, construction was started at the site, with a ground-breaking ceremony. In January 2018, WSP was awarded the contract to manage construction of the Giant Magellan Telescope. The casting of the first mirror, in a rotating furnace, was completed on November 3, 2005. A third segment was cast in August 2013, the fourth in September 2015, the fifth in 2017, the sixth in 2021, and the last in 2023. Polishing of the first mirror was completed in November 2012. Ingersoll Machine Tools finished constructing a manufacturing facility to manufacture the Giant Magellan Telescope mount in Rockford, Illinois, in December 2021. As of 2022, construction of the telescope mount was underway. The structure is expected to be delivered to Chile at the end of 2025.

Enclosure

The Giant Magellan Telescope enclosure is a structure that shelters the telescope's mirrors and components from the extreme weather and earthquakes in the Atacama Desert, Chile. The 4,800-ton enclosure can complete a full rotation in a little more than three minutes and is designed with a closed-cycle forced-air convection system to maintain a thermal equilibrium within the telescope enclosure and reduce ambient thermal gradients across the primary mirror surface. The enclosure design provides the telescope pier with a seismic isolation system that can survive the strongest earthquakes expected over the 50-year lifetime of the observatory and will allow the telescope to quickly return to operations after the more frequent, but less intense seismic events that are experienced several times per month. In March 2022, engineering and architecture firm IDOM was awarded the contract to finalize the telescope's enclosure design by 2024.

Telescope Mount

The telescope mount structure is a alt-azimuth design that will stand on a pier that is in diameter. The structure will weigh 1,800 tons without mirrors and instruments. With mirrors and instruments, it will weigh 2,100 tons. This structure will float on a film of oil (50 microns thick), being supported by a number of hydrostatic bearings to allow the telescope mount to glide frictionlessly in three degrees of freedom. In October 2019, GMTO Corporation announced the signing of a contract with German company MT Mechatronics (subsidiary of OHB SE) and Illinois-based Ingersoll Machine Tools, to design, build and install the Giant Magellan Telescope's structure. Ingersoll Machine Tools finished constructing a 40,000 square foot facility to manufacture the Giant Magellan Telescope mount in Rockford, Illinois in December 2021. As of 2022, construction of the telescope mount was underway and is expected to be completed in 2025. The telescope mount consists of seven "cells" that hold and protect the telescope's 18-ton primary mirrors. The mirror support system does not have a traditional internal load-carrying frame. Instead, the strength comes from its unique shape and external shell. This allows the telescope mount to have a compact and lightweight design for its size. It also makes the telescope extremely stiff and stable so that it can resist image quality interruptions from wind and mechanical vibrations. The "cell" primary mirror support system contains "active optics" with

pneumatic actuators A pneumatic control valve actuator converts energy (typically in the form of compressed air) into mechanical motion. The motion can be rotary or linear, depending on the type of actuator. Principle of operation A pneumatic actuator mainly cons ...

that will push on the back of the primary mirrors to correct for the effects of

gravity In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...

and

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

variations on the seven, primary mirrors. In addition, fourteen air handler units using CO₂-based refrigeration – the first system of its kind used for telescopes – are mounted to the interior of the mirror support system to circulate the air. A closed-cycle forced-air convection system is used to maintain a thermal equilibrium within the telescope enclosure and reduce thermal gradients across the primary mirror surface. As a precursor to the fabrication of the seven mirror support systems, a full-scale prototype has also been built to validate design decisions and demonstrate the performance. In April 2023, OHB Italia S.p.A. finished manufacturing and testing the first of seven mirror covers for the Giant Magellan. In just over two minutes, the covers will retract in unison to protect the world's largest mirrors when not in use.

Primary mirrors

The telescope will use seven of the world's largest mirrors as primary mirror segments, each in diameter. These segments will then be arranged with one mirror in the center and the other six arranged symmetrically around it. The challenge is that the outer six mirror segments will be off-axis, and although identical to each other, will not be individually radially symmetrical, necessitating a modification of the usual polishing and testing procedures. The mirrors are being constructed by the

University of Arizona The University of Arizona (Arizona, U of A, UArizona, or UA) is a Public university, public Land-grant university, land-grant research university in Tucson, Arizona, United States. Founded in 1885 by the 13th Arizona Territorial Legislature, it ...

Steward Observatory Steward Observatory is the research arm of the Department of Astronomy at the University of Arizona (UArizona). Its offices are located on the UArizona campus in Tucson, Arizona (US). Established in 1916, the first telescope and building were ...

Richard F. Caris Mirror Lab. The casting of each mirror uses 20 tons of E6

borosilicate glass Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficients of thermal expansion (≈3 × 10−6 K−1 at 20 °C), ma ...

from the Ohara Corporation of Japan and takes about 12–13 weeks. After being cast, they need to cool for about six months. Each takes approximately 4 years to cast and polish, obtaining a finish that is so smooth that the highest peaks and valleys are smaller than 1/1000 of the width of a human hair. As this was an off-axis segment, a wide array of new optical tests and laboratory infrastructure had to be developed to polish the mirror. The intention is to build seven identical off-axis mirrors, so that a spare is available to substitute for a segment being recoated, a 1–2 week (per segment) process required every 1–2 years. While the complete telescope will use seven mirrors, it is planned to begin operation with four mirrors. Segments 1–3 are complete. Segments 4–6 are undergoing polishing and testing. Segment 7 was planned for casting in 2023. The primary mirror array will have a

focal ratio An f-number is a measure of the light-gathering ability of an optical system such as a camera lens. It is calculated by dividing the system's focal length by the diameter of the entrance pupil ("clear aperture").Smith, Warren ''Modern Optical ...

(focal length divided by diameter) of f/0.71. For an individual segment – one third that diameter – this results in a focal ratio of f/2.14. The overall focal ratio of the complete telescope will be f/8 and the optical prescription is an aplanatic Gregorian telescope. Like all modern large telescopes it will make use of

adaptive optics Adaptive optics (AO) is a technique of precisely deforming a mirror in order to compensate for light distortion. It is used in Astronomy, astronomical telescopes and laser communication systems to remove the effects of Astronomical seeing, atmo ...

. Scientists expect very high quality images due to the very large aperture and advanced adaptive optics. Image quality is projected at a 20-arcminute field of view, correctable from 0–20 arcminutes. The images will be sharp enough to resolve the torch engraved on a U.S. dime from nearly 160 kilometers (100 miles) away and expected to exceed that of the

. The Carnegie Observatories office in Pasadena has an outline of the Giant Magellan primary mirror array painted in its parking lot. It is easily visible in satellite imagery at .

Secondary mirrors and adaptive optics

The Giant Magellan Telescope's Adaptive Secondary Mirror consists of seven segments about in diameter. They are deformable "adaptive optics" mirrors tasked with correcting the atmospheric distortion of the light gathered by the telescope. The Adaptive Secondary Mirrors consist of a thin sheet of glass that is bonded to more than 7000 independently controlled voice coil actuators. Each segment can deform/reshape their 2-millimeter-thick surface 2,000 times per second to correct for the optical blurring effect of Earth's atmosphere. The first segment is under construction as of August 2022 and will be completed in 2024. The Giant Magellan Telescope will have three modes of adaptive optics. *Ground Layer Adaptive Optics (GLAO): The Gregorian design and integrated adaptive optics system allow ground layer atmospheric turbulence to be corrected over a wide field of view, improving natural seeing image quality by 20–50% from the visible to near-infrared (with the greatest improvements at red wavelengths). The Giant Magellan uses wavefront sensors that allow any instrument to receive GLAO corrected images. *Natural Guide Star Adaptive Optics (NGAO): NGAO uses a single natural guide star (bright) to deliver diffraction limited, high Strehl ratio images (>75 % Strehl in the K band) at wavelengths from 0.6 μm into the mid-infrared over a field of view a few arcseconds in diameter. *Laser Tomography Adaptive Optics (LTAO): LTAO uses six laser guide stars and a single natural guide star (faint) to extend diffraction-limited performance to nearly the full sky with moderate Strehl ratio (>30 % Strehl in the H band) at infrared wavelengths over a much wider field of view than NGAO (~20" at 1μm) and is available to any instrument designed to use this mode. The Giant Magellan is the only 30-meter-class telescope with ground layer adaptive optics over a full field of view.

Science instruments

The Giant Magellan Telescope's Gregorian design can accommodate up to 10 visible to mid-infrared science instruments, from wide field imagers and spectrographs that reach hundreds of objects at one time, to high-resolution imagers and spectrographs that can study exoplanets and even find

biosignatures A biosignature (sometimes called chemical fossil or molecular fossil) is any substance – such as an element, isotope, molecule, or phenomenon – that provides scientific evidence of past or present life on a planet. Measurable ...

. Each science instrument is designed to take advantage of the telescope's four observing modes. The telescope will have an advanced fiber-optic system that uses tiny robotic positioners to expand the capabilities of the spectrographs by allowing them to access the highest resolution of all telescopes in the 30-meter class over a full field of view of 20 arcminutes. Using this system, it is possible to observe multiple targets over the entire field with one or more of the spectrographs. This enables the telescope to see fainter objects with unrivaled resolution and sensitivity. The advantage is extremely powerful for spectroscopy and the precise measurements of distances, dynamics, chemistry, and masses of celestial objects in deep space. *GMT-Consortium Large Earth Finder (G-CLEF) – an optical-band echelle spectrograph *GMT Multi-object Astronomical and Cosmological Spectrograph (GMACS) – a visible multi-object spectrograph *GMT Integral-Field Spectrograph (GMTIFS) – a near-IR IFU and AO imager *GMT Near-IR Spectrograph (GMTNIRS) – a near-IR spectrograph *The Many Instrument Fiber System (MANIFEST) – a facility fiber system Additionally, the Commissioning Camera (ComCam) will be used to validate the Ground Layer Adaptive Optics performance of the GMT facility Adaptive Optics System. Science drivers for the Giant Magellan Telescope include studying planets in the habitable zones of their parent star in the search for life; the nature of dark matter, dark energy, gravity, and many other aspects of fundamental physics; the formation and evolution of the first stars and galaxies; and how black holes and galaxies co-evolve.

Comparison

The Giant Magellan Telescope is one of a new class of telescopes called

s with each design being much larger than existing ground-based telescopes. Other planned extremely large telescopes include the

Extremely Large Telescope The Extremely Large Telescope (ELT) is an astronomical observatory under construction. When completed, it will be the world's largest optical and near-infrared extremely large telescope. Part of the European Southern Observatory (ESO) agency, ...

and the

Thirty Meter Telescope The Thirty Meter Telescope (TMT) is a planned extremely large telescope (ELT) proposed to be built on Mauna Kea, on the Hawaii (island), island of Hawai'i. The TMT would become the largest visible-light telescope on Mauna Kea. Scientists hav ...

Organizations

The Giant Magellan Telescope is the work of the GMTO Corporation, an international consortium of research institutions representing seven countries from Australia, Brazil, Chile, Israel, South Korea, Taiwan, and the United States. The GMTO Corporation is a nonprofit

501(c)(3) organization A 501(c)(3) organization is a United States corporation, Trust (business), trust, unincorporated association or other type of organization exempt from federal income tax under section 501(c)(3) of Title 26 of the United States Code. It is one of ...

with offices in Pasadena, California and Santiago, Chile. The organization has an established relationship with the Chilean government, having been recognized through a presidential decree as an "international organization" in Chile. The telescope operates under a cooperative agreement with the University of Chile, granting 10% of the observing time to astronomers working at Chilean institutions. The following organizations are members of the consortium developing the telescope. *

Academia Sinica Institute of Astronomy and Astrophysics An academy (Attic Greek: Ἀκαδήμεια; Koine Greek Ἀκαδημία) is an institution of tertiary education. The name traces back to Plato's school of philosophy, founded approximately 386 BC at Akademia, a sanctuary of Athena, the go ...

Arizona State University Arizona State University (Arizona State or ASU) is a public university, public research university in Tempe, Arizona, United States. Founded in 1885 as Territorial Normal School by the 13th Arizona Territorial Legislature, the university is o ...

* Astronomy Australia Limited *

Australian National University The Australian National University (ANU) is a public university, public research university and member of the Group of Eight (Australian universities), Group of Eight, located in Canberra, the capital of Australia. Its main campus in Acton, A ...

* FAPESP *

Harvard University Harvard University is a Private university, private Ivy League research university in Cambridge, Massachusetts, United States. Founded in 1636 and named for its first benefactor, the History of the Puritans in North America, Puritan clergyma ...

* Korea Astronomy and Space Science Institute (한국천문연구원) (KASI) *

Northwestern University Northwestern University (NU) is a Private university, private research university in Evanston, Illinois, United States. Established in 1851 to serve the historic Northwest Territory, it is the oldest University charter, chartered university in ...

Smithsonian Institution The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums, Education center, education and Research institute, research centers, created by the Federal government of the United States, U.S. government "for the increase a ...

Texas A&M University Texas A&M University (Texas A&M, A&M, TA&M, or TAMU) is a public university, public, Land-grant university, land-grant, research university in College Station, Texas, United States. It was founded in 1876 and became the flagship institution of ...

University of Texas at Austin The University of Texas at Austin (UT Austin, UT, or Texas) is a public university, public research university in Austin, Texas, United States. Founded in 1883, it is the flagship institution of the University of Texas System. With 53,082 stud ...

University of Chicago The University of Chicago (UChicago, Chicago, or UChi) is a Private university, private research university in Chicago, Illinois, United States. Its main campus is in the Hyde Park, Chicago, Hyde Park neighborhood on Chicago's South Side, Chic ...

Weizmann Institute of Science The Weizmann Institute of Science ( ''Machon Weizmann LeMada'') is a Public university, public research university in Rehovot, Israel, established in 1934, fourteen years before the State of Israel was founded. Unlike other List of Israeli uni ...

The Giant Magellan Telescope is a part of the US Extremely Large Telescope Program (US-ELTP), as of 2018. The US-ELTP will provide US-based astronomers with U.S.

National Science Foundation The U.S. National Science Foundation (NSF) is an Independent agencies of the United States government#Examples of independent agencies, independent agency of the Federal government of the United States, United States federal government that su ...

funded all-sky observing access to both the Giant Magellan Telescope and Thirty Meter Telescope. The program was ranked as the highest ground-based priority in the

National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, NGO, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the ...

Astro2020 Decadal Survey, which noted that the US-ELTP will provide "observational capabilities unmatched in space or the ground and open an enormous discovery space for new observations and discoveries not yet anticipated."

References

External links

Giant Magellan Telescope home page

Lecture by director Patrick McCarthy on technologies behind GMT

''New Scientist'' article on the telescope

COSMOS article on the telescope

Painted outline of the mirrors at the parking lot of the Observatories of the Carnegie Institution
in

Pasadena Pasadena ( ) is a city in Los Angeles County, California, United States, northeast of downtown Los Angeles. It is the most populous city and the primary cultural center of the San Gabriel Valley. Old Pasadena is the city's original commercial d ...

J. Rosenberg – Seeing Stars (2013) – ''Harvard Magazine''

{{Portal bar, Astronomy, Stars, Spaceflight, Outer space, Solar System Reflecting telescopes Telescopes under construction Astronomical observatories in Chile Buildings and structures under construction in Chile