Tidal Imprint of Distant Galactic Matter on the Oort Comet Cloud

We report the detection of a remarkably strong nonrandom signal in the distribution of perihelia vectors of Oort cloud comets. The strongest signal is in the Galactic longitudes of perihelia, and we show that it is most likely caused by the adiabatic perturbation of the Galactic radial tide. The probability that the signal in longitude is because of chance is found to be 2 × 10-6. There is also evidence of the adiabatic perturbation of the Galactic tide component which is in a direction normal to the midplane. This is found in the distribution of Galactic latitudes of perihelia but is statistically less significant, a somewhat counterintuitive result since the Galactic z tide has a strength ≈ 16 times that of the Galactic radial tide. We find that ≈ 1/3 of observed Oort cloud comets are attributable to the Galactic radial tide. The source of the Galactic z tide is primarily local disk matter, while the source of the Galactic radial tide is the entire distribution of matter interior to the solar orbit. Consequently, we conclude that distant matter in the Galaxy, down to the Galactic core some 1.6 × 109 AU away, is an important factor in making Oort cloud comets observable.