Submillimetre astronomy

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The Caltech Submillimeter Observatory at Mauna Kea Observatory was commissioned in 1988, and has a 10.4 m (34 ft) dish Caltech-Submillimeter-Observatory (straightened).jpg
The Caltech Submillimeter Observatory at Mauna Kea Observatory was commissioned in 1988, and has a 10.4 m (34 ft) dish

Submillimetre astronomy or submillimeter astronomy (see spelling differences) is the branch of observational astronomy that is conducted at submillimetre wavelengths (i.e., terahertz radiation) of the electromagnetic spectrum. Astronomers place the submillimetre waveband between the far-infrared and microwave wavebands, typically taken to be between a few hundred micrometres and a millimetre. It is still common in submillimetre astronomy to quote wavelengths in 'microns', the old name for micrometre.

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Using submillimetre observations, astronomers examine molecular clouds and dark cloud cores with a goal of clarifying the process of star formation from earliest collapse to stellar birth. Submillimetre observations of these dark clouds can be used to determine chemical abundances and cooling mechanisms for the molecules which comprise them. In addition, submillimetre observations give information on the mechanisms for the formation and evolution of galaxies.

From the ground

Panoramic view of the Chajnantor plateau, spanning about 180 degrees from north (on the left) to south (on the right) shows the antennas of the Atacama Large Millimeter Array. ALMA's World At Night.jpg
Panoramic view of the Chajnantor plateau, spanning about 180 degrees from north (on the left) to south (on the right) shows the antennas of the Atacama Large Millimeter Array.

The most significant limitations to the detection of astronomical emission at submillimetre wavelengths with ground-based observatories are atmospheric emission, noise and attenuation. Like the infrared, the submillimetre atmosphere is dominated by numerous water vapour absorption bands and it is only through "windows" between these bands that observations are possible. The ideal submillimetre observing site is dry, cool, has stable weather conditions and is away from urban population centres. Only a handful of such have been sites identified. They include Mauna Kea (Hawaii, United States), the Llano de Chajnantor Observatory on the Atacama Plateau (Chile), the South Pole, and Hanle in India (the Himalayan site of the Indian Astronomical Observatory). Comparisons show that all four sites are excellent for submillimetre astronomy, and of these sites Mauna Kea is the most established and arguably the most accessible. There has been some recent interest in high-altitude Arctic sites, particularly Summit Station in Greenland where the PWV (precipitable water vapor) measure is always better than at Mauna Kea (however Mauna Kea's equatorial latitude of 19 degrees means it can observe more of the southern skies than Greenland). [1] [2]

The Llano de Chajnantor Observatory site hosts the Atacama Pathfinder Experiment (APEX), the largest submillimetre telescope operating in the southern hemisphere, and the world's largest ground based astronomy project, the Atacama Large Millimeter Array (ALMA), an interferometer for submillimetre wavelength observations made of 54 12-metre and 12 7-metre radio telescopes. The Submillimeter Array (SMA) is another interferometer, located at Mauna Kea, consisting of eight 6-metre diameter radio telescopes. The largest existing submillimetre telescope, the James Clerk Maxwell Telescope, is also located on Mauna Kea.

From the stratosphere

With high-altitude balloons and aircraft, one can get above more of the atmosphere. The BLAST experiment and SOFIA are two examples, respectively, although SOFIA can also handle near infrared observations. [ citation needed ]

From orbit

Comparison [3]
NameYearWavelengthAperture
Human Eye0.39 – 0.75 μm0.01 m
SWAS 1998540 – 610 μm0.55 – 0.7 m
Herschel 200955 – 672 μm3.5 m

Space-based observations at the submillimetre wavelengths remove the ground-based limitations of atmospheric absorption. The first submillimeter telescope in space was the Soviet BST-1M, located in the scientific equipment compartment of the Salyut-6 orbital station. It was equipped with a mirror with a diameter of 1.5 m and was intended for astrophysical research in the ultraviolet (0.2 - 0.36 microns), infrared (60 - 130 microns) and submillimeter (300 - 1000 microns) spectral regions, which are of interest to those who are interested in which makes it possible to study molecular clouds in space, as well as obtain information about the processes taking place in the upper layers of the Earth's atmosphere.

The Submillimeter Wave Astronomy Satellite (SWAS) was launched into low Earth orbit on December 5, 1998 as one of NASA's Small Explorer Program (SMEX) missions. The mission of the spacecraft is to make targeted observations of giant molecular clouds and dark cloud cores. The focus of SWAS is five spectral lines: water (H2O), isotopic water (H218O), isotopic carbon monoxide (13CO), molecular oxygen (O2), and neutral carbon (C I).

The SWAS satellite was repurposed in June, 2005 to provide support for the NASA Deep Impact mission. SWAS provided water production data on the comet until the end of August 2005.

The European Space Agency launched a space-based mission known as the Herschel Space Observatory (formerly called Far Infrared and Sub-millimetre Telescope or FIRST) in 2009. Herschel deployed the largest mirror ever launched into space (until December 2021, with the launch of the near-infrared James Webb Space Telescope) and studied radiation in the far infrared and submillimetre wavebands. Rather than an Earth orbit, Herschel entered into a Lissajous orbit around L2, the second Lagrangian point of the Earth-Sun system. L2 is located approximately 1.5 million km from Earth and the placement of Herschel there lessened the interference by infrared and visible radiation from the Earth and Sun. Herschel's mission focused primarily on the origins of galaxies and galactic formation.

See also

Related Research Articles

Infrared astronomy is a sub-discipline of astronomy which specializes in the observation and analysis of astronomical objects using infrared (IR) radiation. The wavelength of infrared light ranges from 0.75 to 300 micrometers, and falls in between visible radiation, which ranges from 380 to 750 nanometers, and submillimeter waves.

<span class="mw-page-title-main">Far-infrared astronomy</span> Scientific study of celestial objects visible in wavelengths of 30-450 μm

Far-infrared astronomy is the branch of astronomy and astrophysics that deals with objects visible in far-infrared radiation.

<span class="mw-page-title-main">European Southern Observatory</span> Intergovernmental organization and observatory in Chile

The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental research organisation made up of 16 member states 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 over 750 staff members and receives annual member state contributions of approximately €162 million. Its observatories are located in northern Chile.

<span class="mw-page-title-main">Mauna Kea Observatories</span> Astronomical observatories in Hawaii

The Mauna Kea Observatories (MKO) are a group of independent astronomical research facilities and large telescope observatories that are located at the summit of Mauna Kea on the Big Island of Hawaiʻi, United States. The facilities are located in a 525-acre (212 ha) special land use zone known as the "Astronomy Precinct", which is located within the 11,228-acre (4,544 ha) Mauna Kea Science Reserve. The Astronomy Precinct was established in 1967 and is located on land protected by the Historical Preservation Act for its significance to Hawaiian culture. The presence and continued construction of telescopes is highly controversial due to Mauna Kea's centrality in native Hawaiian religion and culture, as well as for a variety of environmental reasons.

<span class="mw-page-title-main">Atacama Large Millimeter Array</span> 66 radio telescopes in the Atacama Desert of northern Chile

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 provides insight on star birth during the early Stelliferous era and detailed imaging of local star and planet formation.

<span class="mw-page-title-main">Herschel Space Observatory</span> ESA space telescope in service 2009–2013

The Herschel Space Observatory was a space observatory built and operated by the European Space Agency (ESA). It was active from 2009 to 2013, and was the largest infrared telescope ever launched until the launch of the James Webb Space Telescope in 2021. Herschel carries a 3.5-metre (11.5 ft) mirror and instruments sensitive to the far infrared and submillimetre wavebands (55–672 µm). Herschel was the fourth and final cornerstone mission in the Horizon 2000 programme, following SOHO/Cluster II, XMM-Newton and Rosetta.

<span class="mw-page-title-main">James Clerk Maxwell Telescope</span> Radio telescope in Hawaii, US

The James Clerk Maxwell Telescope (JCMT) is a submillimetre-wavelength radio telescope at Mauna Kea Observatory in Hawaii, US. 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.

<span class="mw-page-title-main">Caltech Submillimeter Observatory</span> Decommissioned radio telescope in Hawaii, USA

The Caltech Submillimeter Observatory (CSO) was a 10.4-meter (34 ft) diameter submillimeter wavelength telescope situated alongside the 15-meter (49 ft) James Clerk Maxwell Telescope (JCMT) at Mauna Kea Observatories. It was engaged in submillimeter astronomy, of the terahertz radiation band. The telescope closed on September 18, 2015. The telescope is set to be dismantled and its site remediated in the near future as part of the Mauna Kea Comprehensive Management Plan.

<span class="mw-page-title-main">Submillimeter Array</span> Astronomical radio interferometer in Hawaii, USA

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 have been 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. The radio frequencies accessible to this telescope range from 194–408 gigahertz (1.545–0.735 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.

<span class="mw-page-title-main">Atacama Pathfinder Experiment</span> Radio telescope in the Atacama desert, northern Chile

The Atacama Pathfinder Experiment (APEX) is a radio telescope 5,064 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert in northern Chile, 50 km east of San Pedro de Atacama built and operated by 3 European research institutes. The main dish has a diameter of 12 m and consists of 264 aluminium panels with an average surface accuracy of 17 micrometres (rms). The telescope was officially inaugurated on September 25, 2005.

<span class="mw-page-title-main">Heinrich Hertz Submillimeter Telescope</span> Radio telescope in Graham County, Arizona

The Submillimeter Telescope (SMT), formerly known as the Heinrich Hertz Submillimeter Telescope, is a submillimeter wavelength radio telescope located on Mount Graham, Arizona, US. It is a 10-meter-wide parabolic dish inside a building to protect it from bad weather. The building front doors and roof are opened when the telescope is in use. The telescope's construction was finished in 1993. Along with the 12 Meter Telescope on Kitt Peak, this telescope is maintained by the Arizona Radio Observatory, a division of Steward Observatory at the University of Arizona.

<span class="mw-page-title-main">Llano de Chajnantor Observatory</span> Observatory

Llano de Chajnantor Observatory is the name for a group of astronomical observatories located at an altitude of over 4,800 m (15,700 ft) in the Atacama Desert of northern Chile. The site is in the Antofagasta Region approximately 50 kilometres (31 mi) east of the town of San Pedro de Atacama. The exceptionally arid climate of the area is inhospitable to humans, but creates an excellent location for millimeter, submillimeter, and mid-infrared astronomy. This is because water vapour absorbs and attenuates submillimetre radiation. Llano de Chajnantor is home to the largest and most expensive astronomical telescope project in the world, the Atacama Large Millimeter Array (ALMA). Llano de Chajnantor and the surrounding area has been designated as the Chajnantor Science Reserve by the government of Chile.

<span class="mw-page-title-main">Submillimeter Wave Astronomy Satellite</span> NASA satellite of the Explorer program

Submillimeter Wave Astronomy Satellite is a NASA submillimetre astronomy satellite, and is the fourth spacecraft in the Small Explorer program (SMEX). It was launched on 6 December 1998, at 00:57:54 UTC, from Vandenberg Air Force Base aboard a Pegasus XL launch vehicle. The telescope was designed by the Smithsonian Astrophysical Observatory (SAO) and integrated by Ball Aerospace, while the spacecraft was built by NASA's Goddard Space Flight Center (GSFC). The mission's principal investigator is Gary J. Melnick.

Two instruments known as the Submillimetre Common-User Bolometer Array, or SCUBA, have been used for detecting submillimetre radiation on the James Clerk Maxwell Telescope in Hawaii.

<span class="mw-page-title-main">Fred Young Submillimeter Telescope</span> Proposed radio telescope in Antofagasta Region, Chile

The Cerro Chajnantor Atacama Telescope (CCAT) is a proposed 25 metres (82 ft) diameter telescope that is intended to reveal the cosmic origins of stars, planets, and galaxies with its submillimeter cameras and spectrometers enabled by superconducting detector arrays. The telescope was originally called the Cornell Caltech Atacama Telescope, but due to lack of funding the 25 metre telescope is currently on hold.

<span class="mw-page-title-main">Large Latin American Millimeter Array</span>

The Large Latin American Millimeter Array (LLAMA) is a single-dish 12 m Nasmyth optics antenna which is under construction in the Puna de Atacama desert in the Province of Salta, Argentina, next to the Qubic experiment. The primary mirror accuracy will allow observation from 40 GHz up to 900 GHz. 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 and Brazilian governments. 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.

<span class="mw-page-title-main">J band (infrared)</span>

In infrared astronomy, the J band refers to an atmospheric transmission window centred on 1.25 micrometres.

Thomas Gould Phillips was a British-born physicist, who worked primarily in the United States. He was a pioneer in the field of submillimeter astronomy, who both developed new instrumentation and made ground-breaking observations. He oversaw the construction of, and was the first and longest-serving director of the Caltech Submillimeter Observatory.

References

  1. "Recent Interest in Eureka on Ellesmere Island as a Submillimetre Observing Site" (PDF). Archived from the original (PDF) on 2015-07-03.
  2. "ASIAA sub-mm VLBI Project" (PDF).
  3. JPL: Herschel Space Observatory: Related Missions