Atacama Cosmology Telescope
Encyclopedia
Cerro Toco
Cerro Toco is a stratovolcano located in the eastern part of the Atacama desert in Chile's II Region , approximately south of the border between Bolivia and Chile and SE of the Juriques and Licancabur volcanoes...
in the Atacama Desert
Atacama Desert
The Atacama Desert is a plateau in South America, covering a strip of land on the Pacific coast, west of the Andes mountains. It is, according to NASA, National Geographic and many other publications, the driest desert in the world...
in the north of Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
, near the Llano de Chajnantor Observatory
Llano de Chajnantor Observatory
Llano de Chajnantor Observatory is an astronomical observatory located at an altitude of 5,104 m in the Chilean Atacama desert, 50 kilometers to the east of San Pedro de Atacama. It is a very dry site - inhospitable to humans - but an excellent site for submillimetre astronomy...
. It is designed to make high-resolution, microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
-wavelength surveys of the sky in order to study the cosmic microwave background radiation
Cosmic microwave background radiation
In cosmology, cosmic microwave background radiation is thermal radiation filling the observable universe almost uniformly....
(CMB). At an altitude of 5190 metres (17,030 feet), it is one of the highest permanent, ground-based telescopes in the world.
Erected in the (austral) autumn of 2007, ACT saw first light on 22 October 2007 with its science receiver, the Millimeter Bolometer
Bolometer
A bolometer is a device for measuring the power of incident electromagnetic radiation via the heating of a material with a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley...
Array Camera (MBAC), and completed its first season in December 2007. It began its second season of observations in June 2008.
The project is a collaboration between Princeton University
Princeton University
Princeton University is a private research university located in Princeton, New Jersey, United States. The school is one of the eight universities of the Ivy League, and is one of the nine Colonial Colleges founded before the American Revolution....
, the University of Pennsylvania
University of Pennsylvania
The University of Pennsylvania is a private, Ivy League university located in Philadelphia, Pennsylvania, United States. Penn is the fourth-oldest institution of higher education in the United States,Penn is the fourth-oldest using the founding dates claimed by each institution...
, NASA/GSFC
Goddard Space Flight Center
The Goddard Space Flight Center is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight center. GSFC employs approximately 10,000 civil servants and contractors, and is located approximately northeast of Washington, D.C. in Greenbelt, Maryland, USA. GSFC,...
, the University of British Columbia
University of British Columbia
The University of British Columbia is a public research university. UBC’s two main campuses are situated in Vancouver and in Kelowna in the Okanagan Valley...
, NIST, the Pontificia Universidad Católica de Chile, the University of KwaZulu-Natal
University of KwaZulu-Natal
The University of KwaZulu-Natal or UKZN is a university with five campuses all located in the province of KwaZulu-Natal in South Africa. It was formed on 1 January 2004 after the merger between the University of Natal and the University of Durban-Westville.-History:-University of...
, Cardiff University
Cardiff University
Cardiff University is a leading research university located in the Cathays Park area of Cardiff, Wales, United Kingdom. It received its Royal charter in 1883 and is a member of the Russell Group of Universities. The university is consistently recognised as providing high quality research-based...
, Rutgers University
Rutgers University
Rutgers, The State University of New Jersey , is the largest institution for higher education in New Jersey, United States. It was originally chartered as Queen's College in 1766. It is the eighth-oldest college in the United States and one of the nine Colonial colleges founded before the American...
, the University of Pittsburgh
University of Pittsburgh
The University of Pittsburgh, commonly referred to as Pitt, is a state-related research university located in Pittsburgh, Pennsylvania, United States. Founded as Pittsburgh Academy in 1787 on what was then the American frontier, Pitt is one of the oldest continuously chartered institutions of...
, Columbia University
Columbia University
Columbia University in the City of New York is a private, Ivy League university in Manhattan, New York City. Columbia is the oldest institution of higher learning in the state of New York, the fifth oldest in the United States, and one of the country's nine Colonial Colleges founded before the...
, Haverford College
Haverford College
Haverford College is a private, coeducational liberal arts college located in Haverford, Pennsylvania, United States, a suburb of Philadelphia...
, INAOE, LLNL, NASA/JPL, the University of Toronto
University of Toronto
The University of Toronto is a public research university in Toronto, Ontario, Canada, situated on the grounds that surround Queen's Park. It was founded by royal charter in 1827 as King's College, the first institution of higher learning in Upper Canada...
, the University of Cape Town
University of Cape Town
The University of Cape Town is a public research university located in Cape Town in the Western Cape province of South Africa. UCT was founded in 1829 as the South African College, and is the oldest university in South Africa and the second oldest extant university in Africa.-History:The roots of...
, the University of Massachusetts
University of Massachusetts
This article relates to the statewide university system. For the flagship campus often referred to as "UMass", see University of Massachusetts Amherst...
and York College, CUNY
York College, City University of New York
York College of The City University of New York is one of eleven senior colleges in the City University of New York system. It is located in Jamaica, Queens in New York City...
. It is funded by the US National Science Foundation
National Science Foundation
The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...
.
Design and location
The ACT is an off-axis Gregorian telescopeGregorian telescope
The Gregorian telescope is a type of reflecting telescope designed by Scottish mathematician and astronomer James Gregory in the 17th century, and first built in 1673 by Robert Hooke...
, with a six metre (236 in) primary mirror and a two metre (79 in) secondary mirror. Both mirrors are segmented, consisting of 71 (primary) and 11 (secondary) aluminum panels. Unlike most telescopes which track the rotating sky during observation, the ACT observes a strip of sky, typically five degrees wide, by scanning back and forth in azimuth at the relatively rapid rate of two degrees per second. The rotating portion of the telescope weighs approximately 32 tonnes (35 short tons), creating a substantial engineering challenge. A ground screen surrounding the telescope minimises contamination from microwave radiation emitted by the ground. The design, manufacture and construction of the telescope were done by Dynamic Structures in Vancouver
Vancouver
Vancouver is a coastal seaport city on the mainland of British Columbia, Canada. It is the hub of Greater Vancouver, which, with over 2.3 million residents, is the third most populous metropolitan area in the country,...
, British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
.
Observations are made at resolutions of about an arcminute (1/60th of a degree) in three frequencies: 145 GHz, 215 GHz and 280 GHz. Each frequency is measured by a 3 cm x 3 cm (1.2" x 1.2"), 1024 element array, for a total of 3072 detectors. The detectors are superconducting transition-edge sensors, a new technology whose high sensitivity should allow measurements of the temperature of the CMB to within a few millionths of a degree. A system of cryogenic helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
refrigerators keep the detectors a third of a degree above absolute zero
Absolute zero
Absolute zero is the theoretical temperature at which entropy reaches its minimum value. The laws of thermodynamics state that absolute zero cannot be reached using only thermodynamic means....
.
In its currently scheduled survey, the ACT will map about two hundred square degrees of the sky.
Because water vapour in the atmosphere emits microwave radiation which contaminates measurements of the CMB, the telescope benefits from its arid, high-altitude site, located in the lofty — yet easily accessible — Chajnantor plain in the Andean
Andes
The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...
mountains in the Atacama Desert
Atacama Desert
The Atacama Desert is a plateau in South America, covering a strip of land on the Pacific coast, west of the Andes mountains. It is, according to NASA, National Geographic and many other publications, the driest desert in the world...
. Several other observatories are located in the region, including CBI
Cosmic Background Imager
The Cosmic Background Imager was a 13-element interferometer perched at an elevation of 5,080 metres at Llano de Chajnantor Observatory in the Chilean Andes...
, ASTE
Atacama Submillimeter Telescope Experiment
The Atacama Submillimeter Telescope Experiment is a 10m antenna built by Mitsubishi Electric as a preprototype for ALMA.The ASTE was deployed to its site on Pampa La Bola, near Cerro Chajnantor and the Llano de Chajnantor Observatory in northern Chile. The antenna shows excellent performance...
, Nanten
NANTEN2 Observatory
The NANTEN2 Observatory is a southern sky observatory in the Atacama Desert of northern Chile. It is located at an altitude of on Pampa la Bola next to Cerro Chajnantor. The observatory is equipped with a millimeter and submillimeter wave telescope that is used for southern sky observations of...
, APEX
Atacama Pathfinder Experiment
The Atacama Pathfinder Experiment is a radio telescope located at 5,100 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert, in northern Chile, 50 kilometers to the east of San Pedro de Atacama. The main dish has a diameter of 12 meters and consists of 264...
and ALMA
Atacama Large Millimeter Array
The Atacama Large Millimeter/sub-millimeter Array is an array of radio telescopes in the Atacama desert of northern Chile. Since a high and dry site is crucial to millimeter wavelength operations, the array is being constructed on the Chajnantor plateau at 5000 metres altitude...
.
Science goals
Measurements of cosmic microwave background radiationCosmic microwave background radiation
In cosmology, cosmic microwave background radiation is thermal radiation filling the observable universe almost uniformly....
(CMB) by experiments such as COBE
COBE
The COsmic Background Explorer , also referred to as Explorer 66, was a satellite dedicated to cosmology. Its goals were to investigate the cosmic microwave background radiation of the universe and provide measurements that would help shape our understanding of the cosmos.This work provided...
, BOOMERanG
BOOMERanG experiment
The BOOMERanG experiment measured the cosmic microwave background radiation of a part of the sky during three sub-orbital balloon flights. It was the first experiment to make large, high fidelity images of the CMB temperature anisotropies...
, WMAP, CBI
Cosmic Background Imager
The Cosmic Background Imager was a 13-element interferometer perched at an elevation of 5,080 metres at Llano de Chajnantor Observatory in the Chilean Andes...
and many others have greatly advanced our knowledge of cosmology, particularly the early evolution of the universe. It is expected that higher resolution CMB observations will not only improve the precision of current knowledge, but will also allow new types of measurements. At ACT resolutions, the Sunyaev-Zeldovich effect (SZ), by which galaxy clusters leave an imprint on the CMB, should be prominent. The power of this method of detection is that it is a redshift
Redshift
In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...
-independent measurement of the mass of the clusters, meaning that very distant, ancient clusters are as easy to detect as nearby clusters.
It is expected that ACT will detect on the order of 100 such clusters. Together with follow-up measurements in visible and X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
light, this would provide a picture of the evolution of structure in the universe since the Big Bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...
. Among other things, this would improve our understanding of the nature of the mysterious Dark Energy
Dark energy
In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...
which seems to be a dominant component of the universe.
The South Pole Telescope
South Pole Telescope
The South Pole Telescope is a 10 metre diameter telescope located at the Amundsen-Scott South Pole Station, Antarctica. It is a microwave/millimetre-wave telescope that observes in a frequency range between 70 and 300 GHz...
has similar, but complementary, science objectives.
Results
ACT released results measuring the statistical properties of the temperature of the CMB down to arcminute scales in January 2010. It found signals that were consistent with un-resolved point sources and the SZ effect. In 2011, ACT made the first detection of the power spectrum of gravitational lensing of the microwave background, which, combined with the WMAP results, has for the first time provided evidence for dark energyDark energy
In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...
from the CMB
CMB
CMB can mean:*The IATA airport code for Bandaranaike International Airport, Colombo – Sri Lanka's only international airport*C.M.B., the debut album of American R&B and pop group Color Me Badd...
alone.