BICEP and Keck Array

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BICEP
PIA17993-DetectorsForInfantUniverseStudies-20140317.jpg
The BICEP2 detector array under a microscope
Alternative namesBackground Imaging of Cosmic Extragalactic Polarization OOjs UI icon edit-ltr-progressive.svg
Part of Amundsen–Scott South Pole Station   OOjs UI icon edit-ltr-progressive.svg
Location(s)Antarctic Treaty area
Coordinates 89°59′59″S0°00′00″E / 89.999722°S 0°E / -89.999722; 0 OOjs UI icon edit-ltr-progressive.svg
Wavelength 95, 150, 220 GHz (3.2, 2.0, 1.4 mm)
Telescope style cosmic microwave background experiment
radio telescope   OOjs UI icon edit-ltr-progressive.svg
Diameter0.25 m (9.8 in) OOjs UI icon edit-ltr-progressive.svg
Website www.cfa.harvard.edu/CMB/keckarray/ OOjs UI icon edit-ltr-progressive.svg
Antarctica relief location map.jpg
Red pog.svg
Location of BICEP and Keck Array
  Commons-logo.svg Related media on Commons
[ edit on Wikidata]

BICEP (Background Imaging of Cosmic Extragalactic Polarization) and the Keck Array are a series of cosmic microwave background (CMB) experiments. They aim to measure the polarization of the CMB; in particular, measuring the B-mode of the CMB. The experiments have had five generations of instrumentation, consisting of BICEP1 (or just BICEP), BICEP2, the Keck Array, BICEP3, and the BICEP Array. The Keck Array started observations in 2012 and BICEP3 has been fully operational since May 2016, with the BICEP Array beginning installation in 2017/18.

Contents

Purpose and collaboration

Gravitational waves may arise from inflation, a phase of accelerated expansion after the Big Bang. History of the Universe.svg
Gravitational waves may arise from inflation, a phase of accelerated expansion after the Big Bang.

The purpose of the BICEP experiment is to measure the polarization of the cosmic microwave background. [5] Specifically, it aims to measure the B-modes (curl component) of the polarization of the CMB. [6] BICEP operates from Antarctica, at the Amundsen–Scott South Pole Station. [5] All three instruments have mapped the same part of the sky, around the south celestial pole. [5] [7]

The institutions involved in the various instruments are Caltech, Cardiff University, University of Chicago, Center for Astrophysics | Harvard & Smithsonian, Jet Propulsion Laboratory, CEA Grenoble (FR), University of Minnesota and Stanford University (all experiments); UC San Diego (BICEP1 and 2); National Institute of Standards and Technology (NIST), University of British Columbia and University of Toronto (BICEP2, Keck Array and BICEP3); and Case Western Reserve University (Keck Array). [6] [8] [9] [10] [11]

The series of experiments began at the California Institute of Technology in 2002. In collaboration with the Jet Propulsion Laboratory, physicists Andrew Lange, Jamie Bock, Brian Keating, and William Holzapfel began the construction of the BICEP1 telescope which deployed to the Amundsen-Scott South Pole Station in 2005 for a three-season observing run. [12] Immediately after deployment of BICEP1, the team, which now included Caltech postdoctoral fellows John Kovac and Chao-Lin Kuo, among others, began work on BICEP2. The telescope remained the same, but new detectors were inserted into BICEP2 using a completely different technology: a printed circuit board on the focal plane that could filter, process, image, and measure radiation from the cosmic microwave background. BICEP2 was deployed to the South Pole in 2009 to begin its three-season observing run which yielded the detection of B-mode polarization in the cosmic microwave background.

BICEP1

The first BICEP instrument (known during development as the "Robinson gravitational wave background telescope") observed the sky at 100 and 150 GHz (3 mm and 2 mm wavelength) with an angular resolution of 1.0 and 0.7 degrees. It had an array of 98 detectors (50 at 100 GHz and 48 at 150 GHz), which were sensitive to the polarisation of the CMB. [5] A pair of detectors constitutes one polarization-sensitive pixel. The instrument, a prototype for future instruments, was first described in Keating et al. 2003 [13] and started observing in January 2006 [6] and ran until the end of 2008. [5]

BICEP2

South pole spt dsl.jpg
BICEP2 telescope near South Pole Telescope
Antarctica (11235782635).jpg
Keck Array at Martin A. Pomerantz Observatory

The second-generation instrument was BICEP2. [14] Featuring a greatly improved focal-plane transition edge sensor (TES) bolometer array of 512 sensors (256 pixels) operating at 150 GHz, this 26 cm aperture telescope replaced the BICEP1 instrument, and observed from 2010 to 2012. [15] [16]

Reports stated in March 2014 that BICEP2 had detected B-modes from gravitational waves in the early universe (called primordial gravitational waves), a result reported by the four co-principal investigators of BICEP2: John M. Kovac of the Center for Astrophysics | Harvard & Smithsonian; Chao-Lin Kuo of Stanford University; Jamie Bock of the California Institute of Technology; and Clem Pryke of the University of Minnesota.

An announcement was made on 17 March 2014 from the Center for Astrophysics | Harvard & Smithsonian. [1] [2] [3] [4] [17] The reported detection was of B-modes at the level of r = 0.20+0.07
−0.05, disfavouring the null hypothesis (r = 0) at the level of 7 sigma (5.9σ after foreground subtraction). [15] However, on 19 June 2014, lowered confidence in confirming the cosmic inflation findings was reported; [18] [19] the accepted and reviewed version of the discovery paper contains an appendix discussing the possible production of the signal by cosmic dust. [15] In part because the large value of the tensor to scalar ratio, which contradicts limits from the Planck data, [20] this is considered the most likely explanation for the detected signal by many scientists. For example, on June 5, 2014 at a conference of the American Astronomical Society, astronomer David Spergel argued that the B-mode polarization detected by BICEP2 could instead be the result of light emitted from dust between the stars in our Milky Way galaxy. [21]

A preprint released by the Planck team in September 2014, eventually accepted in 2016, provided the most accurate measurement yet of dust, concluding that the signal from dust is the same strength as that reported from BICEP2. [22] [23] On January 30, 2015, a joint analysis of BICEP2 and Planck data was published and the European Space Agency announced that the signal can be entirely attributed to dust in the Milky Way. [24]

BICEP2 has combined their data with the Keck Array and Planck in a joint analysis. [25] A March 2015 publication in Physical Review Letters set a limit on the tensor-to-scalar ratio of r < 0.12.

The BICEP2 affair forms the subject of a book by Brian Keating.

Keck Array

The main properties of the BICEP instruments
InstrumentStartEndFrequencyResolutionSensors (pixels)Refs
BICEP 20062008100 GHz0.93°50 (25) [5] [6]
150 GHz0.60°48 (24) [5]
BICEP2 20102012150 GHz0.52°500 (250) [15]
Keck Array 20112011150 GHz0.52°1488 (744) [7] [26]
201220122480 (1240)
201320181488 (744) [26]
95 GHz0.7°992 (496)
BICEP3 2015—95 GHz0.35°2560 (1280) [27]

Immediately next to the BICEP telescope at the Martin A. Pomerantz Observatory building at the South Pole was an unused telescope mount previously occupied by the Degree Angular Scale Interferometer. [28] The Keck Array was built to take advantage of this larger telescope mount. This project was funded by $2.3 million from W. M. Keck Foundation, as well as funding from the National Science Foundation, the Gordon and Betty Moore Foundation, the James and Nelly Kilroy Foundation and the Barzan Foundation. [6] The Keck Array project was originally led by Andrew Lange. [6]

The Keck Array consists of five polarimeters, each very similar to the BICEP2 design, but using a pulse tube refrigerator rather than a large liquid helium cryogenic storage dewar.

The first three started observations in the austral summer of 2010–11; another two started observing in 2012. All of the receivers observed at 150 GHz until 2013, when two of them were converted to observe at 100 GHz. [26] Each polarimeter consists of a refracting telescope (to minimise systematics) cooled by a pulse tube cooler to 4 K, and a focal-plane array of 512 transition edge sensors cooled to 250 mK, giving a total of 2560 detectors, or 1280 dual-polarization pixels. [7]

In October 2018, the first results from the Keck Array (combined with BICEP2 data) were announced, using observations up to and including the 2015 season. These yielded an upper limit on cosmological B-modes of (95% confidence level), which reduces to in combination with Planck data. [29]

In October 2021, new results were announced giving (at 95% confidence level) based on BICEP/Keck 2018 observation season combined with Planck and WMAP data. [30] [31]

BICEP3

Once the Keck array was completed in 2012, it was no longer cost-effective to continue to operate BICEP2. However, using the same technique as the Keck array to eliminate the large liquid helium dewar, a much larger telescope has been installed on the original BICEP telescope mount.

BICEP3 consists of a single telescope with the same 2560 detectors (observing at 95 GHz) as the five-telescope Keck array, but a 68 cm aperture, [32] providing roughly twice the optical throughput of the entire Keck array. One consequence of the large focal plane is a larger 28° field of view, [33] which will necessarily mean scanning some foreground-contaminated portions of the sky. It was installed (with initial configuration) at the pole in January 2015. [27] [34] It was upgraded for the 2015-2016 Austral summer season to a full 2560 detector configuration. BICEP3 is also a prototype for the BICEP Array. [35]

BICEP Array

The Keck array is being succeeded by the BICEP array, which consists of four BICEP3-like telescopes on a common mount, operating at 30/40, 95, 150 and 220/270 GHz. [36] Installation began between the 2017 and 2018 observing seasons. It is scheduled to be fully installed by the 2020 observing season. [37] [38]

According to the project website: "BICEP Array will measure the polarized sky in five frequency bands to reach an ultimate sensitivity to the amplitude of IGW [inflationary gravitational waves] of σ(r) < 0.005" and "This measurement will be a definitive test of slow-roll models of inflation, which generally predict a gravitational-wave signal above approximately 0.01." [37]

See also

Related Research Articles

<span class="mw-page-title-main">Physical cosmology</span> Branch of cosmology which studies mathematical models of the universe

Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fundamental questions about its origin, structure, evolution, and ultimate fate. Cosmology as a science originated with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed those physical laws to be understood.

<span class="mw-page-title-main">Cosmic microwave background</span> Electromagnetic radiation as a remnant from an early stage of the universe in Big Bang cosmology

The cosmic microwave background is microwave radiation that fills all space in the observable universe. It is a remnant that provides an important source of data on the primordial universe. With a standard optical telescope, the background space between stars and galaxies is almost completely dark. However, a sufficiently sensitive radio telescope detects a faint background glow that is almost uniform and is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. The accidental discovery of the CMB in 1965 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s.

<span class="mw-page-title-main">Wilkinson Microwave Anisotropy Probe</span> NASA satellite of the Explorer program

The Wilkinson Microwave Anisotropy Probe (WMAP), originally known as the Microwave Anisotropy Probe, was a NASA spacecraft operating from 2001 to 2010 which measured temperature differences across the sky in the cosmic microwave background (CMB) – the radiant heat remaining from the Big Bang. Headed by Professor Charles L. Bennett of Johns Hopkins University, the mission was developed in a joint partnership between the NASA Goddard Space Flight Center and Princeton University. The WMAP spacecraft was launched on 30 June 2001 from Florida. The WMAP mission succeeded the COBE space mission and was the second medium-class (MIDEX) spacecraft in the NASA Explorer program. In 2003, MAP was renamed WMAP in honor of cosmologist David Todd Wilkinson (1935–2002), who had been a member of the mission's science team. After nine years of operations, WMAP was switched off in 2010, following the launch of the more advanced Planck spacecraft by European Space Agency (ESA) in 2009.

In physical cosmology, the inflationary epoch was the period in the evolution of the early universe when, according to inflation theory, the universe underwent an extremely rapid exponential expansion. This rapid expansion increased the linear dimensions of the early universe by a factor of at least 1026 (and possibly a much larger factor), and so increased its volume by a factor of at least 1078. Expansion by a factor of 1026 is equivalent to expanding an object 1 nanometer (10−9 m, about half the width of a molecule of DNA) in length to one approximately 10.6 light years (about 62 trillion miles) long.

Clover would have been an experiment to measure the polarization of the Cosmic Microwave Background. It was approved for funding in late 2004, with the aim of having the full telescope operational by 2009. The project was jointly run by Cardiff University, Oxford University, the Cavendish Astrophysics Group and the University of Manchester.

<i>Planck</i> (spacecraft) European cosmic microwave background observatory; medium-class mission in the ESA Science Programme

Planck was a space observatory operated by the European Space Agency (ESA) from 2009 to 2013. It was an ambitious project that aimed to map the anisotropies of the cosmic microwave background (CMB) at microwave and infrared frequencies, with high sensitivity and small angular resolution. The mission was highly successful and substantially improved upon observations made by the NASA Wilkinson Microwave Anisotropy Probe (WMAP).

<span class="mw-page-title-main">South Pole Telescope</span> Telescope at the South Pole

The South Pole Telescope (SPT) is a 10-metre (390 in) diameter telescope located at the Amundsen–Scott South Pole Station, Antarctica. The telescope is designed for observations in the microwave, millimeter-wave, and submillimeter-wave regions of the electromagnetic spectrum, with the particular design goal of measuring the faint, diffuse emission from the cosmic microwave background (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 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 mapping speed over SPTpol.

<span class="mw-page-title-main">Atacama Cosmology Telescope</span> Telescope in the Atacama Desert, northern Chile

The Atacama Cosmology Telescope (ACT) was a cosmological millimeter-wave telescope located on Cerro Toco in the Atacama Desert in the north of Chile. ACT made high-sensitivity, arcminute resolution, microwave-wavelength surveys of the sky in order to study the cosmic microwave background radiation (CMB), the relic radiation left by the Big Bang process. Located 40 km from San Pedro de Atacama, at an altitude of 5,190 metres (17,030 ft), it was one of the highest ground-based telescopes in the world.

The Degree Angular Scale Interferometer (DASI) was a telescope installed at the U.S. National Science Foundation's Amundsen–Scott South Pole Station in Antarctica. It was a 13-element interferometer operating between 26 and 36 GHz in ten bands. The instrument is similar in design to the Cosmic Background Imager (CBI) and the Very Small Array (VSA). In 2001 The DASI team announced the most detailed measurements of the temperature, or power spectrum of the Cosmic microwave background (CMB). These results contained the first detection of the 2nd and 3rd acoustic peaks in the CMB, which were important evidence for inflation theory. This announcement was done in conjunction with the BOOMERanG and MAXIMA experiment. In 2002 the team reported the first detection of polarization anisotropies in the CMB.

<span class="mw-page-title-main">Spider (polarimeter)</span>

Spider is a balloon-borne experiment designed to search for primordial gravitational waves imprinted on the cosmic microwave background (CMB). Measuring the strength of this signal puts limits on inflationary theory.

<span class="mw-page-title-main">Archeops</span>

Archeops was a balloon-borne instrument dedicated to measuring the Cosmic microwave background (CMB) temperature anisotropies. The study of this radiation is essential to obtain precise information on the evolution of the Universe: density, Hubble constant, age of the Universe, etc. To achieve this goal, measurements were done with devices cooled down at 100mK temperature placed at the focus of a warm telescope. To avoid atmospheric disturbance the whole apparatus is placed on a gondola below a helium balloon that reaches 40 km altitude.

<span class="mw-page-title-main">QUIET</span>

QUIET was an astronomy experiment to study the polarization of the cosmic microwave background radiation. QUIET stands for Q/U Imaging ExperimenT. The Q/U in the name refers to the ability of the telescope to measure the Q and U Stokes parameters simultaneously. QUIET was located at an elevation of 5,080 metres at Llano de Chajnantor Observatory in the Chilean Andes. It began observing in late 2008 and finished observing in December 2010.

<span class="mw-page-title-main">POLARBEAR</span>

POLARBEAR is a cosmic microwave background polarization experiment located in the Atacama Desert of northern Chile in the Antofagasta Region. The POLARBEAR experiment is mounted on the Huan Tran Telescope (HTT) at the James Ax Observatory in the Chajnantor Science Reserve. The HTT is located near the Atacama Cosmology Telescope on the slopes of Cerro Toco at an altitude of nearly 5,200 m (17,100 ft).

<span class="mw-page-title-main">Cosmology Large Angular Scale Surveyor</span>

The Cosmology Large Angular Scale Surveyor (CLASS) is an array of microwave telescopes at a high-altitude site in the Atacama Desert of Chile as part of the Parque Astronómico de Atacama. The CLASS experiment aims to improve our understanding of cosmic dawn when the first stars turned on, test the theory of cosmic inflation, and distinguish between inflationary models of the very early universe by making precise measurements of the polarization of the Cosmic Microwave Background (CMB) over 65% of the sky at multiple frequencies in the microwave region of the electromagnetic spectrum.

John Michael Kovac is an American physicist and astronomer. His cosmology research, conducted at the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Massachusetts, focuses on observations of the Cosmic Microwave Background (CMB) to reveal signatures of the physics that drove the birth of the universe, the creation of its structure, and its present-day expansion. Currently, Kovac is Professor of Astronomy and Physics at Harvard University.

<span class="mw-page-title-main">Atacama B-Mode Search</span>

The Atacama B-Mode Search (ABS) was an experiment to test the theory of cosmic inflation and distinguish between inflationary models of the very early universe by making precise measurements of the polarization of the Cosmic Microwave Background (CMB). ABS was located at a high-altitude site in the Atacama Desert of Chile as part of the Parque Astronómico de Atacama. ABS began observations in February 2012 and completed observations in October 2014.

<span class="mw-page-title-main">Simons Observatory</span>

The Simons Observatory is located in the high Atacama Desert in Northern Chile inside the Chajnator Science Preserve, at an altitude of 5,200 meters (17,000 ft). The Atacama Cosmology Telescope (ACT) and the Simons Array are located nearby and these experiments are currently making observations of the Cosmic Microwave Background (CMB). Their goals are to study how the universe began, what it is made of, and how it evolved to its current state. The Simons Observatory shares many of the same goals but aims to take advantage of advances in technology to make far more precise and diverse measurements. In addition, it is envisaged that many aspects of the Simons Observatory will be pathfinders for the future CMB-S4 array.

LiteBIRD is a planned small space observatory that aims to detect the footprint of the primordial gravitational wave on the cosmic microwave background (CMB) in a form of polarization pattern called B-mode.

In cosmological inflation, within the slow-roll paradigm, the Lyth argument places a theoretical upper bound on the amount of gravitational waves produced during inflation, given the amount of departure from the homogeneity of the cosmic microwave background (CMB).

References

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