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Abstract:

We calculate solar models including dark matter (DM) weakly interacting massive particles (WIMPs) of mass 5-50 GeV and test these models against helioseismic constraints on sound speed, convection-zone depth, convection-zone helium abundance, and small separations of low-degree p-modes. Our main conclusion is that both direct detection experiments and particle accelerators may be complemented by using the Sun as a probe for WIMP DM particles in the 5-50 GeV mass range. The DM most sensitive to this probe has suppressed annihilations and a large spin-dependent elastic scattering cross section. For the WIMP cross section parameters explored here, the lightest WIMP masses <10 GeV are ruled out by constraints on core sound speed and low-degree frequency spacings. For WIMP masses 30-50 GeV, the changes to the solar structure are confined to the inner 4% of the solar radius and so do not significantly affect the solar p-modes. Future helioseismology observations, most notably involving g-modes, and future solar neutrino experiments may be able to constrain the allowable DM parameter space in a mass range that is of current interest for direct detection. © 2010 The American Physical Society.

Abstract:

Galaxy formation is significantly modulated by energy output from supermassive black holes at the centers of galaxies which grow in highly efficient luminous quasar phases. The timescale on which black holes transition into and out of such phases is, however, unknown. We present the first measurement of the shutdown timescale for an individual quasar using X-ray observations of the nearby galaxy IC 2497, which hosted a luminous quasar no more than 70,000 years ago that is still seen as a light echo in `Hanny's Voorwerp', but whose present-day radiative output is lower by at least 2 and more likely by over 4 orders of magnitude. This extremely rapid shutdown provides new insights into the physics of accretion in supermassive black holes, and may signal a transition of the accretion disk to a radiatively inefficient state.

Abstract:

We present a measurement of the angular power spectrum of the cosmic microwave background (CMB) radiation observed at 148 GHz. The measurement uses maps with 1′.4 angular resolution made with data from the Atacama Cosmology Telescope (ACT). The observations cover 228 deg² of the southern sky, in a 4°.2 wide strip centered on declination 53° south. The CMB at arcminute angular scales is particularly sensitive to the Silk damping scale, to the Sunyaev-Zel'dovich (SZ) effect from galaxy clusters, and to emission by radio sources and dusty galaxies. After masking the 108 brightest point sources in our maps, we estimate the power spectrum between 600 < â„“ < 8000 using the adaptive multi-taper method to minimize spectral leakage and maximize use of the full data set. Our absolute calibration is based on observations of Uranus. To verify the calibration and test the fidelity of our map at large angular scales, we cross-correlate the ACT map to the WMAP map and recover the WMAP power spectrum from 250 < â„“ < 1150. The power beyond the Silk damping tail of the CMB (â„“ ∼ 5000) is consistent with models of the emission from point sources. We quantify the contribution of SZ clusters to the power spectrum by fitting to a model normalized to σ 8 = 0.8. We constrain the model's amplitude ASZ < 1.63 (95% CL). If interpreted as a measurement of σ 8, this implies σ 8^SZ < 0.86 (95% CL) given our SZ model. A fit of ACT and WMAP five-year data jointly to a six-parameter ACDM model plus point sources and the SZ effect is consistent with these results. © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.