Imprint of Distortions in the Oort Cloud on the CMB Anisotropies

We study the effect of a close encounter of a passing star on the shape of the inner Oort Cloud, using the impulse approximation. The deviation of the perturbed Oort Cloud from sphericity adds angular fluctuations to the brightness of the Cosmic Microwave Background (CMB) due to thermal emission by the comets. An encounter with a solar-mass star at an impact parameter of 2100AU, as expected based on the abundance and velocity dispersion of stars in the solar neighborhood, leads to a quadrupole moment C2 = 4.5(3.5) × 10−15, 6.7(1.1) × 10−12, 1.1(0.11) × 10−9 at ν = 30, 353, 545GHz, respectively in intensity and (temperature) fluctuations. We also quantify the quadrupole spectral distortions produced by the Scattered Disc, which will exist irregardless of any perturbation and the subsequent shape of the Oort Cloud. For comparison, the temperature fluctuation quadrupole moment predicted by the current cosmological model is C2 = 1.76 × 10−10, which corresponds to fluctuation in the CMB intensity of C2 = 2.9 × 10−10, 6.8 × 10−9, 1.6 × 10−8 at ν = 30, 353, 545GHz. Finally, we discuss how a measurement of the anisotropic spectral distortions could be used to constrain the trajectory of the closest stellar fly-by.