The Giant Magellan Telescope
Alternative namesGMT
Part ofLas Campanas Observatory Edit this on Wikidata
Location(s)Vallenar, Trehuaco, Huasco Province, Atacama Region, Chile
Coordinates29°02′54″S 70°41′01″W / 29.048217°S 70.683575°W / -29.048217; -70.683575
Altitude2,516 m (8,255 ft)
Wavelength320 nm (940 THz)–25,000 nm (12 THz)
Built2015–2025 (2015–2025)
Telescope styleGregorian telescope Edit this on Wikidata
Diameter25.448 m (83 ft 5.9 in)
Secondary diameter3.2 m (10 ft 6 in)
Angular resolution0.01 arcsecond Edit this on Wikidata
Collecting area368 m2 (3,960 sq ft)
Focal length18, 202.7 m (59 ft 1 in, 665 ft 0 in)
Websitegiantmagellan.org
Giant Magellan Telescope is located in Chile
Giant Magellan Telescope
Location of Giant Magellan Telescope
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The Giant Magellan Telescope (Giant Magellan or GMT) is a 25.4-meter, ground-based, extremely large telescope under construction at Las Campanas Observatory in Chile's Atacama Desert. Commissioning is anticipated in the late 2020s.[1][2][3] Once complete, the Giant Magellan will be the largest Gregorian telescope ever built observing in optical and mid-infrared (320–25000 nm[4]) light. The telescope uses seven of the world’s largest mirrors to form a light collecting area of 368 square meters.[5][6]

The Giant Magellan Telescope is expected to have a resolving power 10 times that of the Hubble Space Telescope and four times that of the James Webb Space Telescope, although it will be unable to image in the same infrared frequencies available to telescopes in space. Scientists will use the Giant Magellan to study nearly all aspects of astrophysics — from searching for signs of life on distant exoplanets to investigating the cosmic origins of chemical elements.[7][8][9][10] The Giant Magellan Telescope began casting its primary mirrors in 2005 and started site construction in 2015. As of 2023, all seven of the primary mirrors have been cast, the first of seven adaptive secondary mirrors are underway, and manufacturing of the telescope mount is underway. Other telescope subsystems are in final design stages.[11][12][13]

The USD $2 billion scale telescope is the work of the GMTO Corporation, an international consortium of leading research institutions representing six countries: Australia, Brazil, Chile, Israel, South Korea, and the United States.[14]

Site

Giant Magellan Telescope Construction Site Aerial View

The location of the telescope is Las Campanas Observatory,[15] which is also the site of the Magellan Telescopes, some 115 km (71 mi) north-northeast of La Serena, Chile and 180 km (112 mi) south of Copiapó, Chile, at an altitude of 2,516 m (8,255 ft).[16][17] The site has been owned by Carnegie Institution for Science's since 1960. The site has been chosen as the telescope’s location because of its outstanding astronomical seeing and clear weather throughout most of the year.[18] Moreover, due to the sparsity of population centers and other favorable geographical conditions, the night sky in most of the surrounding Atacama Desert region is not only free from atmospheric pollution, but in addition it is probably one of the places least affected by light pollution, making the area one of the best spots on Earth for long-term astronomical observation. The southern hemisphere location provides access to the galactic center of the Milky Way, the nearest supermassive black hole (proximity to Sagittarius A*), the nearest star to our Sun (Proxima Centauri), the Magellanic Clouds, and many of the closest galaxies and exoplanets.[8][9]

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.[19]

Table: Performance Specifications

Optical PrescriptionAplanatic Gregorian
Focal Plane Scale0.997 arcseconds/mm
Wavelength Range0.32–25 um
Field of View20 arcminute diameter
Primary Mirror Diameter & Collecting Area25.4 m, 368 m²
Primary Mirror f/#0.71
Mirror f/#Finalƒ/# (with Wide Field Corrector)8.16 [8.34]
Diffraction-limited Angular Resolution0.01 arcsecond at 1 um

Site preparation began with the first blast to level the mountain peak on March 23, 2012.[20] 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.[21]

The casting of the first mirror, in a rotating furnace, was completed on November 3, 2005.[22][23] A third segment was cast in August 2013,[12][24] the fourth in September 2015,[25] the fifth in 2017,[26] the sixth in 2021,[10] and the last in 2023.[13]

Polishing of the first mirror was completed in November 2012.[27]

Ingersoll Machine Tools finished constructing of a manufacturing facility to manufacture the Giant Magellan Telescope mount in Rockford, Illinois in December 2021. As of 2022, construction of the telescope mount is underway. The structure is expected to be delivered to Chile at the end of 2025.[28][29]

Enclosure

The Giant Magellan Telescope enclosure is a 65-meter-tall 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 nearly 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.[30]

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.[30]

In March 2022, engineering and architecture firm IDOM was awarded the contract to finalize the telescope’s enclosure design by 2024.[31]

Telescope Mount

The telescope mount structure is an 39 meters tall alt-azimuth design and it will stand on a pier that is 22 meters 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.[32]

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 is underway and is expected to be completed in 2025.[32]

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.[32]

The “cell” primary mirror support system contains “active optics” with pneumatic actuators will push on the back of the primary mirrors to correct for the effects of gravity and temperature variations on the seven, 8.4 meter diameter primary mirrors.[33] In addition, fourteen air handler units utilizing 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.[34]

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.[34]

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.[32]

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.[35]

Primary mirrors

Giant Magellan Telescope Primary Mirror Back Surface
Comparison of nominal sizes of apertures of the Giant Magellan Telescope and some notable optical telescopes

The telescope will use seven of the world's largest mirrors as primary mirror segments, each 8.417 m (27.61 ft) 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.[36]

The mirrors are being constructed by the University of Arizona's Steward Observatory Richard F. Caris Mirror Lab.[37]

The casting of each mirror uses 20 tons of E6 borosilicate glass from the Ohara Corporation of Japan and takes about 12–13 weeks.[38] After being cast, they need to cool for about six months.[12] 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.[12]

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.[39] While the complete telescope will use seven mirrors, it is planned to begin operation with four mirrors.[12]

Segments 1-3 are complete. Segments 4-6 are undergoing polishing and testing. Segment 7 is planned for casting in 2023.[12]

The primary mirror array will have a focal ratio (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.[24] 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.[40][41]

Scientists expect very high quality images due to the very large aperture and advanced adaptive optics. Image quality is projected at 20 arcminute field of view, correctable from 0-20 arcminute. The images will be sharp enough to resolve the torch engraved on a dime from nearly 160 kilometers (100 miles) away and expected to exceed that of the Hubble Space Telescope.[42]

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 34°09′21″N 118°08′00″W / 34.15591°N 118.13345°W / 34.15591; -118.13345 (Giant Magellan Telescope outline drawing).[43]

Secondary mirrors and adaptive optics

The Giant Magellan Telescope’s Adaptive Secondary Mirror consists of seven segments about 1.1 meters 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.[7]

The first segment is under construction as of August 2022 and will be completed in 2024.[7]

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 diraction-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 the only 30-meter class telescope with ground layer adaptive optics over a full field of view.[44]

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. 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 will expand the capabilities of the spectrographs by allowing them to access highest resolution of all telescopes in the 30-meter class over a full wield 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[45]
  • GMT Multi-object Astronomical and Cosmological Spectrograph (GMACS) - a visible multi-object spectrograph[46]
  • GMT Integral-Field Spectrograph (GMTIFS) - a near-IR IFU and AO imager[47]
  • GMT Near-IR spectrograph (GMTNIRS) - a near-IR spectrograph[48]
  • The Many Instrument Fiber System (MANIFEST) - a facility fiber system[49]

Additionally the Commissioning Camera (ComCam) will be used to validate the Ground Layer Adaptive Optics performance of the GMT facility Adaptive Optics System.[50]

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.[51]

Comparison

The Giant Magellan Telescope is one of a new class of telescopes called extremely large telescopes with each design being much larger than existing ground-based telescopes.[52] Other planned extremely large telescopes include the Extremely Large Telescope and the Thirty Meter Telescope.[53]

NameAperture
diameter (m)		Collecting
area (m2)		First light
Extremely Large Telescope (ELT)39.39782028
Thirty Meter Telescope (TMT)30655 ?[54]
Giant Magellan Telescope (GMT)25.43682029[55]
Southern African Large Telescope (SALT)11.1 × 9.8792005
Keck Telescopes10.0761990, 1996
Gran Telescopio Canarias (GTC)10.4742007
Very Large Telescope (VLT)8.2501998-2000
Notes: future dates for first-light are provisional and are likely to change.

Organizations

The Giant Magellan Telescope is the work of the GMTO Corporation, an international consortium of research institutions representing six countries from Australia, Brazil, Chile, Israel, South Korea, and the United States.[8][56] The GMTO Corporation is a nonprofit 501(c)(3) organization 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.[57][7] The following organizations are members of the consortium developing the telescope.[58]

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 NSF 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 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."[59]

See also

References

  1. ↑ Science Book 2018 GMT Science Book
  2. ↑ Harvard & Smithsonian (6 February 2022). "Mission Critical: Giant Magellan Telescope Ranked a National Priority". SciTechDaily. Retrieved 7 February 2022.
  3. ↑ Diaz, Jesus (16 August 2022). "These next-gen telescopes will make the James Webb look like a toy - Upcoming telescope designs will dwarf the resolution of the James Webb. One of them is coming very soon to a mountain in Chile. The other may take a century". Fast Company. Retrieved 17 August 2022.
  4. ↑ "Giant Magellan Telescope Science Requirements" (PDF). GMT Consortium. p. 11. Retrieved 2008-03-31.
  5. ↑ Maggie McKee (2007-10-04). "Giant telescope in race to become world's largest". New Scientist. Retrieved 2007-10-07.
  6. ↑ "Chapter 6: Optics". GMT Conceptual Design Report. GMT Consortium. pp. 6–3. Archived from the original (PDF) on 2011-06-09. Retrieved 2008-04-02.
  7. 1 2 3 4 "'Magic Mirrors' Will Power The Giant Magellan Telescope". Forbes. August 2, 2022.
  8. 1 2 3 Amos, Jonathan (12 November 2015). "Giant Magellan Telescope: Super-scope project breaks ground". BBC News. Retrieved 2015-11-15.
  9. 1 2 "The Giant Magellan Telescope Organization Breaks Ground in Chile". Giant Magellan Telescope. November 11, 2015.
  10. 1 2 "Engineering Marvel: Sixth Mirror Cast for Giant Magellan Telescope". Giant Magellan Telescope (Press release). 5 March 2021. Retrieved 8 August 2022.
  11. ↑ Proceedings of Spie Giant Magellan
  12. 1 2 3 4 5 6 "Giant Magellan Milestone". Harvard Magazine. August 27, 2013.
  13. 1 2 "The Giant Magellan Telescope's Final Mirror Fabrication Begins". GMTO.
  14. ↑ New $2 Billion Telescope Will Be Fitted With A ‘Large Earth Finder’ Forbes
  15. ↑ "Giant Magellan telescope site selected". Carnegie Institution. Retrieved 2007-10-05.
  16. ↑ José Terán U.; Daniel H. Neff; Matt Johns (2006-05-29). Conceptual design study of the GMT enclosure (PDF). SPIE 6267: Symposium on Astronomical Telescopes and Instrumentation. Orlando, Florida: SPIE. p. 2. Archived from the original (PDF) on 2017-08-09. Retrieved 2008-03-31.
  17. ↑ Joanna Thomas-Osip (2007-03-20), "The Seeing and Turbulence Profile at Las Campanas Observatory: GMT Site Testing Progress Report" (PDF), Syposium on Seeing, Kona, Hawaii: AAS, p. 3, retrieved 2008-03-31
  18. ↑ Robinson, Travis (2007-04-03). "Eye on the sky". The Battalion. Archived from the original on 2007-09-29. Retrieved 2007-04-03.
  19. ↑ "Overview and status of the Giant Magellan Telescope project" (PDF). Giant Magellan. April 12, 2023.
  20. ↑ "Construction of Giant Telescope Begins With Explosion Today: Watch Live". NBC News. March 23, 2012.
  21. ↑ "Giant Magellan Telescope". Aerospace Technology. July 27, 2023.
  22. ↑ Ketelsen, Dean (2012-01-15), GMT polishing at Mirror Lab open house 14 Jan, 2012, archived from the original on 2021-12-12, retrieved 2012-04-08, While guests toured the facilities, the Lab staff ran both of our polishing machines on current projects, including this view of final polishing on the first GMT segment.
  23. ↑ "Mirror Casting Event for the Giant Magellan Telescope" (Press release). GMTO. 2012-01-09. Archived from the original on 2012-04-11.
  24. 1 2 Steward Observatory Mirror Lab, Mirror Castings, archived from the original on 2012-06-23, retrieved 2012-04-08
  25. ↑ "Richard F. Caris Mirror Lab Casts Fourth GMT Segment" (Press release). GMTO. September 18, 2015.
  26. ↑ "Giant Magellan Telescope Organization Casts Fifth Mirror". Giant Magellan Telescope (Press release). 3 November 2017.
  27. ↑ "World's Most Advanced Mirror for Giant Telescope Completed". Australian National University. 2012-11-09. Archived from the original on 2013-03-14. Retrieved 2012-01-14.
  28. ↑ "Giant Magellan Telescope signs contract for telescope structure | Giant Magellan Telescope". 30 October 2019. Retrieved 2020-01-04.
  29. ↑ "December 2019 | Giant Magellan Telescope". Retrieved 2020-01-04.
  30. 1 2 "The GMT site, enclosure, and facilities: 2020 design and construction update". SPIE. December 13, 2020.
  31. ↑ "Giant Magellan Telescope Awards IDOM Final Design of its Telescope Enclosure". University of Chicago. March 8, 2022.
  32. 1 2 3 4 "The Giant Magellan Telescope mount: the core of a next generation 25.4-m aperture ELT". SPIE. August 29, 2022.
  33. ↑ "Science and Technology | Giant Magellan Telescope | Wavefront Control". Retrieved 2020-01-04.
  34. 1 2 "Progress summary of the Giant Magellan Telescope primary mirror off-axis segment active optics control system risk reduction effort: the Test Cell". SPIE digital library. August 29, 2022.
  35. ↑ "Giant Magellan Telescope: The first XL cover is ready". OHB Italia. March 30, 2023.
  36. ↑ What is Optical Metrology?, GMTO, archived from the original on 2012-03-28, retrieved 2012-04-08
  37. ↑ "Home | Richard F. Caris Mirror Lab". Mirrorlab.arizona.edu. Retrieved 2022-12-24.
  38. ↑ Mittan, Kyle (2012-01-16). "Steward Observatory casts second mirror for Giant Magellan Telescope". The Daily Wildcat.
  39. ↑ "Telescope Structure". GMT Conceptual Design Report. February 2006. p. 7-17 § 7.4.5. Archived from the original (PDF) on 2012-03-28. Retrieved 2007-10-07. The center segment and cell will not have a spare, thus observations will be interrupted every one or two years for the 1–2 week period required to recoat that mirror.
  40. ↑ "Chapter 2: Overview", GMT Conceptual Design Report, 2006, p. 2-4 § 2.5.1, archived from the original (PDF) on 2012-03-28, retrieved 2012-03-25, GMT is designed from the outset around adaptive optics (AO) with the goal of producing diffraction limited images at 1 μm and longer wavelengths.
  41. ↑ Hippler, Stefan (2019). "Adaptive Optics for Extremely Large Telescopes". Journal of Astronomical Instrumentation. 8 (2): 1950001–322. arXiv:1808.02693. Bibcode:2019JAI.....850001H. doi:10.1142/S2251171719500016. S2CID 119505402.
  42. ↑ Amos, Jonathan (3 June 2015). "Magellan super-scope gets green light for construction". BBC News. Retrieved 2015-06-04.
  43. ↑ "Giant Magellan Telescope Organization names WSP as Construction Manager". www.gmto.org. January 11, 2018. Retrieved 2018-01-25.
  44. ↑ "Science Book 2018" (PDF). Giant Magellan. December 1, 2018.
  45. ↑ "G-CLEF – The GMT-Consortium Large Earth Finder". gclef.cfa.harvard.edu. Retrieved 2020-01-04.
  46. ↑ "GMACS -Texas A&M Astronomical Instrumentation". Texas A&M University, College Station, TX.
  47. ↑ Director, RSAA; webmaster@mso.anu.edu.au. "Giant Magellan Telescope Integral-Field Spectrograph (GMTIFS)". rsaa.anu.edu.au. Retrieved 2020-01-04.
  48. ↑ "GMTNIRS". www.as.utexas.edu. Retrieved 2020-01-04.
  49. ↑ "MANIFEST | Australian Astronomical Observatory". Australian Astronomical Observatory.
  50. ↑ "Commissioning Camera – ComCam | Giant Magellan Telescope". Retrieved 2020-01-04.
  51. ↑ "Science and Technology | Giant Magellan Telescope | Adaptive Optics". Retrieved 2020-01-04.
  52. ↑ "GMT Overview -- Giant Magellan Telescope". Archived from the original on 2011-06-09. Retrieved 2011-06-15.
  53. ↑ "About TMT -- Thirty Meter Telescope". Archived from the original on 2011-08-08. Retrieved 2011-06-15.
  54. ↑ TMT Timeline, accessed February 11, 2018
  55. ↑ "Giant Magellan Telescope - Quick Facts". Retrieved 16 November 2019.
  56. ↑ "Weizmann Institute of Science joins Giant Magellan Telescope project". The Jerusalem Post. Retrieved 2023-10-12.
  57. ↑ "Excavation of GMT pier and enclosure foundations complete | Giant Magellan Telescope". 16 March 2019.
  58. ↑ "Founders | Giant Magellan Telescope". GMTO Corporation. Retrieved 2018-02-11.
  59. ↑ "Giant Magellan Telescope Is Ranked a National Priority". Smithsonian. November 9, 2021.
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