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Vol 23, May 2007 NEWSLETTER FOR THE Canadian Antarctic Research Network BOOMERANG: Exploring the Universe from the Antarctic Sky Carrie MacTavish Inside In January of 2003, the BOOMERANG telescope completed a second successful Antarctic mission, probing the oldest light in the Universe, addressing the most BOOMERANG: fundamental of cosmological questions and testing the parameters of Big Bang Exploring the Universe Theory. The BOOMERANG group is an international collaboration of 35 scientists from the Antarctic Sky 1 from Canada, Italy, the United States and the U.K. The Canadian contingent is from the University of Toronto (Departments of Physics and Astronomy) and First Light for the the Canadian Institute for Theoretical Astrophysics. The latter played the lead South Pole Telescope 5 role in data analysis, while the former took the lead on the telescope motion control and pointing instrumentation. Part of the team is shown in Figure 1. The First Research Cruise to Study Adaptations and Evolution results from this mission were published in 2006 (Jones and others, 2006; Mac- of Fauna after the Collapse of Tavish and others, 2006; Masi and others, 2006; Montroy and others, 2006; Pia- the Larsen A and B Ice Shelves 8 centini and others, 2006). BOOMERANG is a balloon-borne, microwave telescope designed to measure Restoration of Shackleton’s the Cosmic Microwave Background (CMB). The CMB is one of the firm predictions Nimrod Hut at Cape Royds 12 of Big Bang theory and is a field of electromagnetic radiation that is cosmic in origin, that is originating from the Universe itself. It radiates in the microwave News in Brief 13 (0.3–630 GHz), with a near perfect black-body spectrum which peaks at 160.4 GHz, corresponding to a temperature of 2.725 K. The CMB covers the entire sky and appears as a background to all other objects, for instance stars, galaxies, etc. It was first detected in 1965 by Penzias and Wilson (1965) and has been mea- sured since then by countless instruments with ever-increasing sensitivity. In the most generic scenario, Big Bang theory predicts that the Universe is expanding and that it was hotter and denser in the past than it is now. When it was less than ~300,000 years old there was a period when the scattering rates of 2 matter and radiation exceeded the expansion rate, resulting in near equilibrium conditions for the Universe’s constit- uents. At some point after the first few hundred thousand years, the Universe expanded and cooled enough so that matter and radiation eventually decoupled. At this time, protons and electrons combined to form neutral hydrogen and the photons were allowed to travel freely throughout Figure 1 (above) Part of the BOOMERANG collaboration (with penguin visitor) during pre-launch instrument integration. Figure 2 (left) Hard at work early in the Antarctic campaign. Figure 3 (right) Flight-ready payload. the Universe. The surface from which CMB photons last scat- tered is often referred to as the last scattering or decoupling surface. The CMB photons observed today offer a snapshot of the Universe in its infancy. While the CMB is extremely uniform, there are tiny fluctuations in its intensity and polarization. These trace tiny non-uniformities in the early Universe which grow into the large-scale structure observed in the sky today. The fluctuations in the photon density appear as CANADIAN ANTARCTIC RESEARCH NETWORK 3 BOOMERANG measures light at 145 GHz, 245 GHz and 345 GHz. The instrument is mounted on a ~5 m tall aluminum frame or gondola and the entire flight-ready payload is ~1650 kg. The gondola has an inner frame which can be driven in elevation and an outer frame which scans in azimuth. The flight tra- jectory is determined by the Antarctic wind patterns at float altitude. BOOMERANG’s extremely sensitive bolometric detectors are cooled to < 0.3 K in a liquid helium/liquid nitrogen cryostat. Both the cryostat and the telescope, with its 1.3 m mirror, are mounted on the gondola’s inner frame. Figures 2 and 3 show the instrument at two times during the 2003 Antarctic campaign. The entire payload is hung on steel cables 3 from a ~800,000 m helium-filled balloon, provided by the NASA National Scientific Balloon Facility (NSBF now CSBF). Payloads can reach altitudes of 35 km, above about 99.5% of the Earth’s noisy atmosphere. Ideally, the Antarc- tic vortex winds carry the instrument around the continent at latitude ~78°S in 10–24 days. With 24 hours daylight, the Antarctic flight environment is thermally relatively stable, in anisotropies in the CMB radiation field. Deviations from the contrast to day/night flights at lower latitudes. mean intensity in the primordial plasma are in the order of After some two months of instrument integration and –5 10 and for polarization are an order of magnitude smaller. testing, BOOMERANG was launched on 6 January 2003 from It is these tiny deviations from uniformity that the BOOM- McMurdo and terminated 15 days later. Despite dropping ERANG telescope targets. 171 kg of ballast, the payload altitude dropped daily. The The 2003 mission marked the instrument’s second flight path (Fig. 4) was further complicated by low-altitude successful trip over the Antarctic. The first long-duration winds which kept the balloon in the same spot for nearly balloon flight, in December 1998, resulted in landmark, high five days. The payload landed on the Antarctic Plateau near signal-to-noise maps of the CMB intensity fluctuations (De Dome Fuji, at 3810 m a.s.l., close to the Pole of Inaccessibili- Bernardis and others, 2000; Netterfield and others, 2002). ty. In spite of the rather inconvenient final location, the For the latest flight the instrument was redesigned to be data vessel was recovered within a week and the rest of the polarization sensitive and the attitude control system was instrument salvaged the following year. upgraded to enable more accurate telescope pointing. 4 tions. These include the Planck Satellite mission, for which the BOOMERANG detectors served as a testbed, and SPIDER, a future balloon-borne polarimeter. SPIDER will test the latest CMB detector technology during an around-the-world, 25- day flight from Alice Springs, Australia in 2010. References De Bernardis, P. and 35 others. 2000. A flat universe from high- resolution maps of the cosmic microwave background radiation. Nature, 404(6781), 955–959. Jones, W.C. and 36 others. 2006. A measurement of the angular power spectrum of the CMB temperature anisotropy from the 2003 flight of BOOMERANG. Astrophys. J., 647(2), Part 1, 823–832. MacTavish, C.J. and 37 others. 2006. Cosmological parameters from the 2003 flight of BOOMERANG. Astrophys. J., 647(2), Part 1, 799–812. Masi, S. and 43 others. 2006. Instrument, method, brightness, Figure 4 and polarization maps from the 2003 flight of BOOMERanG. The BOOMERANG flight path. Figure provided by NSBF. Astron. Astrophys., 458(3), 687–716. Montroy, T.E. and 36 others. 2006. A measurement of the CMB EE spectrum from the 2003 flight of BOOMERANG. Astrophys. J., The final BOOMERANG sky coverage from the 2003 647(2), Part 1, 813–822. flight comprised 195 hours of data over 1.8% of the sky. ~ ~ Netterfield, C.B. and 32 others. 2002. A measurement by BOOMER- The resulting BOOMERANG intensity maps are the most pre- ANG of multiple peaks in the angular power spectrum of the cise intermediate-scale measurement of CMB intensity cosmic microwave background. Astrophys. J., 571(2), Part 1, anisotropy to date. The polarization measurement is roughly 604–614 a 5σ detection. These can be used to constrain the cosmo- Penzias, A.A. and R.W. Wilson. 1965. A measurement of excess logical parameters of the standard Big Bang model, e.g., the antenna temperature at 4080 Mc/s. Astrophys. J., 142(1), 419–421 energy density and geometry of the Universe. While the po- Piacentini, F. and 36 others. 2006. A measurement of the polariza- larization data are not yet of an accuracy equivalent to the tion-temperature angular cross-power spectrum of the cosmic intensity data (i.e., they cannot be used to independently microwave background from the 2003 flight of BOOMERANG. constrain cosmological parameters) cross checks of best-fit Astrophys. J., 647(2), Part 1, 833–839. cosmological parameters from both the polarization and intensity data indicate consistent results. Dr Carrie MacTavish ([email protected]) is a post- Efforts to obtain higher-precision measurements of the doctoral fellow at the Canadian Institute for Theoretical CMB polarization continue in order to provide an ever clear- Astrophysics, a nationally supported research center for er picture of the origins of time and space. Canadians are studies in theoretical astronomy and related subjects hosted involved in two upcoming projects which target CMB polar- by the University of Toronto. ization measurements above and beyond the current detec- CANADIAN ANTARCTIC RESEARCH NETWORK 5 First Light for the South Pole Telescope Matt Dobbs on behalf of the South Pole Telescope Collaboration The South Pole Telescope (http://spt.uchicago.edu, SPT) is a Antarctic summer, keep light reflected off the snow from mm-wavelength instrument designed to measure small entering the telescope optics. angular scale features in the Cosmic Microwave Background The $19.2 million telescope is funded primarily by the (CMB) radiation. This afterglow light from the Big Bang was National Science Foundation (NSF), with additional support released when the universe was 400,000 years old – long from the Kavli Foundation of Oxnard, California, and the before planets, stars, and galaxies had time to form. Gordon and Betty Moore Foundation of San Francisco.

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