The South Pole Telescope (SPT) is a diameter telescope located at the
Amundsen–Scott South Pole Station
The Amundsen–Scott South Pole Station is a science and technology in the United States, United States scientific research station at the South Pole of the Earth. It is the List of extreme points of the United States, southernmost point under ...
, Antarctica. The telescope is designed for observations in the
microwave
Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequency, frequencies between 300&n ...
,
millimeter-wave, and
submillimeter-wave regions of the
electromagnetic spectrum
The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high ...
, with the particular design goal of measuring the faint, diffuse emission from the
cosmic microwave background
The cosmic microwave background (CMB, CMBR), or relic radiation, is microwave radiation that fills all space in the observable universe. With a standard optical telescope, the background space between stars and galaxies is almost completely dar ...
(CMB).
Key results include a wide and deep survey of discovering hundreds of clusters of galaxies using the
Sunyaev–Zel'dovich effect, a sensitive 5 arcminute CMB power spectrum survey, and the first detection of B-mode polarized CMB.
The first major survey with the SPT—designed to find distant, massive,
clusters of galaxies through their interaction with the CMB, with the goal of constraining the
dark energy
In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. It also slows the rate of structure format ...
equation of state—was completed in October 2011. In early 2012, a new camera (SPTpol) was installed on the SPT with even greater sensitivity and the capability to measure the polarization of incoming light. This camera operated from 2012–2016 and was used to make unprecedentedly deep high-resolution maps of hundreds of square degrees of the Southern sky. In 2017, the third-generation camera SPT-3G was installed on the telescope, providing nearly an order-of-magnitude increase in detectors in the focal plane.
The SPT collaboration is made up of over a dozen (mostly North American) institutions, including the
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 ...
, the
University of California, Berkeley
The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California), is a Public university, public Land-grant university, land-grant research university in Berkeley, California, United States. Founded in 1868 and named after t ...
,
Case Western Reserve University
Case Western Reserve University (CWRU) is a Private university, private research university in Cleveland, Ohio, United States. It was established in 1967 by a merger between Western Reserve University and the Case Institute of Technology. Case ...
,
Harvard
Harvard University is a private Ivy League research university in Cambridge, Massachusetts, United States. Founded in 1636 and named for its first benefactor, the Puritan clergyman John Harvard, it is the oldest institution of higher lear ...
/
Smithsonian Astrophysical Observatory
The Smithsonian Astrophysical Observatory (SAO) is a research institute of the Smithsonian Institution, concentrating on Astrophysics, astrophysical studies including Galactic astronomy, galactic and extragalactic astronomy, cosmology, Sun, solar ...
, the
University of Colorado Boulder
The University of Colorado Boulder (CU Boulder, CU, or Colorado) is a public research university in Boulder, Colorado, United States. Founded in 1876, five months before Colorado became a state, it is the flagship university of the University o ...
,
McGill University
McGill University (French: Université McGill) is an English-language public research university in Montreal, Quebec, Canada. Founded in 1821 by royal charter,Frost, Stanley Brice. ''McGill University, Vol. I. For the Advancement of Learning, ...
,
Michigan State University
Michigan State University (Michigan State or MSU) is a public university, public Land-grant university, land-grant research university in East Lansing, Michigan, United States. It was founded in 1855 as the Agricultural College of the State o ...
,
The University of Illinois at Urbana-Champaign,
University of California, Davis
The University of California, Davis (UC Davis, UCD, or Davis) is a Public university, public Land-grant university, land-grant research university in Davis, California, United States. It is the northernmost of the ten campuses of the University ...
,
Ludwig Maximilian University of Munich
The Ludwig Maximilian University of Munich (simply University of Munich, LMU or LMU Munich; ) is a public university, public research university in Munich, Bavaria, Germany. Originally established as the University of Ingolstadt in 1472 by Duke ...
,
Argonne National Laboratory
Argonne National Laboratory is a Federally funded research and development centers, federally funded research and development center in Lemont, Illinois, Lemont, Illinois, United States. Founded in 1946, the laboratory is owned by the United Sta ...
, and the
Fermi National Accelerator Laboratory. It is funded by the
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 ...
and the
Department of Energy.
Microwave and millimeter-wave observations at the South Pole
The South Pole region is the premier observing site in the world for millimeter-wavelength observations. The Pole's high altitude of above sea level means the atmosphere is thin, and the extreme cold keeps the amount of water vapor in the air low.
This is particularly important for observing at millimeter wavelengths, where incoming signals can be
absorbed by water vapor, and where water vapor emits radiation that can be confused with astronomical signals. Since the sun does not rise and set daily, the atmosphere at the pole is particularly stable. In addition, no interference exists from the sun in the millimeter range during the months of
polar night
Polar night is a phenomenon that occurs in the polar regions of Earth, northernmost and southernmost regions of Earth when the Sun remains below the horizon for more than 24 hours. This only occurs inside the polar circles. The opposite phen ...
.
The telescope
The telescope is a 10-meter (394 in) diameter off-axis
Gregorian telescope in an
altazimuth mount
An altazimuth mount or alt-azimuth mount is a simple two- axis mount for supporting and rotating an instrument about two perpendicular axes – one vertical and the other horizontal. Rotation about the vertical axis varies the azimuth (compass b ...
(at the poles, an altazimuth mount is effectively identical to an
equatorial mount
An equatorial mount is a mount for instruments that compensates for Earth's rotation by having one rotational axis, called ''polar axis'', parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescope mount, tel ...
). It was designed to allow a large field of view (over 1 square degree) while minimizing systematic uncertainties from ground spill-over and scattering off the telescope optics. The surface of the telescope mirror is smooth down to roughly , or about one-thousandth of an
inch
The inch (symbol: in or prime (symbol), ) is a Units of measurement, unit of length in the imperial units, British Imperial and the United States customary units, United States customary System of measurement, systems of measurement. It is eq ...
(i.e., one
thou
The word ''thou'' () is a second-person singular pronoun in English. It is now largely archaic, having been replaced in most contexts by the word '' you'', although it remains in use in parts of Northern England and in Scots (). ''Thou' ...
), which allows sub-millimeter wavelength observations. A key advantage of the SPT observing strategy is that the entire telescope is scanned, so the beam does not move relative to the telescope mirrors. The fast scanning of the telescope and its large field of view makes SPT efficient at surveying large areas of sky, which is required to achieve the science goals of the SPT cluster survey and CMB polarization measurements.
The SPT-SZ camera
The first camera installed on the SPT contained a 960-element
bolometer
A bolometer is a device for measuring radiant heat by means of a material having a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley.
Principle of operation
A bolometer ...
array of superconducting
transition edge sensors (TES), which made it one of the largest TES bolometer arrays ever built. The focal plane for this camera (referred to as the SPT-SZ camera because it was designed to conduct a survey of galaxy clusters through their
Sunyaev–Zel'dovich effect signature) was split into six pie-shaped wedges, each with 160 detectors. These wedges observed at three different frequencies: 95 GHz, 150 GHz, and 220 GHz. The modularity of the focal plane allowed it to be broken into many different frequency configurations. For the majority of the life of the camera, the SPT-SZ focal plane had one wedge at 95 GHz, four at 150 GHz, and one at 220 GHz. The SPT-SZ camera was used primarily to conduct a survey of 2500 square degrees of the Southern sky (20h to 7h in right ascension, −65d to −40d declination) to a noise level of roughly 15 micro-Kelvin in a 1-arcminute pixel at 150 GHz.
The SPTpol camera
The second camera installed on the SPT–also designed with superconducting TES arrays–was even more sensitive than the SPT-SZ camera and, crucially, had the ability to measure the polarization of the incoming light (hence the name SPTpol – South Pole Telescope POLarimeter). The 780 polarization-sensitive pixels (each with two separate TES bolometers, one sensitive to each linear polarization) were divided between observing frequencies of 90 GHz and 150 GHz, and pixels at the two frequencies are designed with different detector architectures. The 150 GHz pixels were corrugated-feedhorn-coupled TES polarimeters fabricated in monolithic arrays at the National Institute of Standards and Technology. The 90 GHz pixels were individually packaged dual-polarization absorber-coupled polarimeters developed at Argonne National Laboratory. The 90 GHz pixels were coupled to the telescope optics through individually machined contoured feedhorns.
The first year of SPTpol observing was used to survey a 100-square-degree field centered at R.A. 23h30m declination −55d. The next four years were primarily spent surveying a 500-square-degree region of which the original 100 square degrees is a subset. These are currently the deepest high-resolution maps of the millimeter-wave sky over more than a few square degrees, with the noise level at 150 GHz around 5 micro-Kelvin-arcminute and square root of two deeper on the 100-square-degree field.
The SPT-3G camera
In January 2017, the third-generation camera SPT-3G was installed on the SPT. Taking advantage of a combination of improvements to the optical system (providing a significantly larger diffraction-limited field of view) and new detector technology (enabling detectors in multiple observing bands in a single pixel), the SPT-3G detector array contains over ten times more sensors than SPTpol, translating almost directly into a tenfold increase in the speed with which the telescope and camera can map a patch of sky to a given noise level. The camera consists of over 16,000 detectors, split evenly between 90, 150, and 220 GHz.
In 2018, a new survey began using the SPT-3G camera. This survey was to cover 1500 square degrees to a depth of < 3 micro-Kelvin-arcminute at 150 GHz. Significantly, this field overlaps completely with the
BICEP Array observing field, enabling joint analyses of SPT and BICEP data which will deliver significantly better constraints on a potential signal from primordial gravitational waves than either instrument can provide alone.
Science goals and results
The first key project for the SPT, completed in October 2011, was a 2500-
square degree
__NOTOC__
A square degree (deg2) is a non- SI unit measure of solid angle. Other denotations include ''sq. deg.'' and (°)2. Just as degrees are used to measure parts of a circle, square degrees are used to measure parts of a sphere.
Analogous ...
survey to search for
clusters of galaxies using the
Sunyaev–Zel'dovich effect, a distortion of the
cosmic microwave background radiation
The cosmic microwave background (CMB, CMBR), or relic radiation, is microwave radiation that fills all space in the observable universe. With a standard optical telescope, the background space between stars and galaxies is almost completely dar ...
(CMB) due to interactions between CMB photons and the
Intracluster medium
In astronomy, the intracluster medium (ICM) is the superheated plasma (physics), plasma that permeates a galaxy cluster. The gas consists mainly of ionized hydrogen and helium and accounts for most of the baryonic material in galaxy clusters. The ...
in galaxy clusters. The survey has found hundreds of
clusters of galaxies over an extremely wide redshift range.
When combined with accurate
redshift
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and e ...
s and mass estimates for the clusters, this survey will place interesting constraints on the
dark energy
In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. It also slows the rate of structure format ...
equation of state.
Data from the SPT-SZ survey have also been used to make the most sensitive existing measurements of the CMB power spectrum at angular scales smaller than roughly 5 arcminutes (multipole number larger than 2000)
and to discover a population of distant, gravitationally lensed dusty, star-forming galaxies.
Data from the SPTpol camera was used to make several groundbreaking measurements, including the first detection of the so-called "B-mode" or "curl" component of the polarized CMB. This B-mode signal is generated at small angular scales by the gravitational lensing of the much larger primordial "E-mode" polarization signal (generated by scalar density perturbations at the time the CMB was emitted)
and at large angular scales by the interaction of the CMB with a background of gravitational waves produced during the epoch of inflation.
Measurements of the large-scale B-mode signal have the potential to constrain the energy scale of inflation, thus probing the physics of the universe at the earliest times and highest energy scales imaginable, but these measurements are limited by contamination from the lensing B modes. Using the larger E-mode component of the polarization and measurements of the CMB lensing potential, an estimate can be made of the lensing B modes and used to clean the large-scale measurements. This B-mode delensing was first demonstrated using SPTpol data. SPTpol data also has been used to make the most precise measurements of the E-mode power spectrum and temperature-E-mode correlation spectrum of the CMB and to make high-signal-to-noise maps of the projected matter density using reconstructions of the CMB lensing potential.
The 1500-square-degree SPT-3G survey will be used to achieve multiple science goals, including unprecedented constraints on a background of primordial gravitational waves joint analysis of B-mode polarization with the
BICEP Array, a unique sample of distant galaxy clusters for cosmological and cluster evolution studies, and constraints on fundamental physics such as the mass of the neutrinos and the existence of light relic particles in the early Universe.
The
Atacama Cosmology Telescope has similar, but complementary, science objectives.
Funding
The South Pole Telescope is funded through the National Science Foundation Office of Polar Programs and the
United States Department of Energy
The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and energy production, the research and development of nuclear power, the military's nuclear w ...
, with additional support from the
Kavli Foundation and the
Gordon and Betty Moore Foundation
The Gordon and Betty Moore Foundation is an American foundation established by Intel co-founder Gordon E. Moore and his wife Betty I. Moore in September 2000 to support scientific discovery, environmental conservation, patient care improvements ...
. Funding for the SPTpol and SPT-3G instruments and operations are also provided by the United States Department of Energy Office of Science, Office of High Energy Physics.
Operations
On , the South Pole Telescope achieved first light. Formal science observations began in March 2007. Commissioning observations and an initial small survey were completed during austral winter 2007 with winter-overs Stephen Padin and Zak Staniszewski at its helm.
In 2008, larger survey fields were completed with winter-overs Keith Vanderlinde and Dana Hrubes, and in 2009 with winter-overs Erik Shirokoff and Ross Williamson.
In December 2009, the camera was upgraded again for the 2010 observing season. The full 2500 square-degree SPT-SZ survey was completed during the 2010 and 2011 observing seasons with winter-overs Dana Hrubes and Daniel Luong-Van.
First light (the first observation) with the SPTpol camera was achieved on January 27, 2012. During the first season of observations, the winterover crew, Cynthia Chiang and Nicholas Huang, took data on a 100 square degree survey field. 2013 winterovers Dana Hrubes and Jason Gallicchio surveyed a larger field as part of the full SPTpol survey. This larger survey was completed by 2014 winterovers Robert Citron and Nicholas Huang, 2015 winterovers Charlie Sievers and Todd Veach, and 2016 winterovers Christine Corbett Moran and Amy Lowitz. The first winter of SPT-3G observing was conducted by winterovers Daniel Michalik and Andrew Nadolski. Adam Jones and Joshua Montgomery followed in 2018, with Douglas Howe and David Riebel wintering in 2019, Geoff Chen and Allen Foster in 2020, Sasha Rahlin and Matt Young in 2021, Aman Chokshi and Allen Foster in 2022, and Kyle Ferguson and Alex Pollak in 2023.
See also
*
BICEP and Keck Array
*
Cosmological constant
In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: ), alternatively called Einstein's cosmological constant,
is a coefficient that Albert Einstein initially added to his field equations of general rel ...
*
List of astronomical observatories
This is a partial list of astronomical observatories ordered by name, along with initial dates of operation (where an accurate date is available) and location. The list also includes a final year of operation for many observatories that are no lon ...
*
Lists of telescopes
This is a list of lists of telescopes.
*List of astronomical interferometers at visible and infrared wavelengths
*List of astronomical observatories
*List of highest astronomical observatories
*List of large optical telescopes
*List of largest i ...
References
External links
South Pole Telescope Official SiteLife at the South Pole– Blog of Keith Vanderlinde, who operated the telescope during the 2008 season
{{Portal bar, Astronomy, Stars, Spaceflight, Outer space, Solar System, Education, Science
Submillimetre telescopes
Radio telescopes
Cosmic microwave background experiments
Astronomical observatories in the Antarctic
2007 establishments in Antarctica