We demonstrate the existence of an enhanced rate of angular momentum relaxation in nearly Keplerian star clusters, such as those found in the centers of galactic nuclei containing massive black holes. The enhanced relaxation arises because the radial and azimuthal orbital frequencies in a Keplerian potential are equal, and hence may be termed resonant relaxation. We explore the dynamics of resonant relaxation using both numerical simulations and order-of-magnitude analytic calculations. We find that the resonant angular momentum relaxation time is shorter than the non-resonant relaxation time by of order M ⋆ /M, where M ⋆ is the mass in stars and M is the mass of the central object. Resonance does not enhance the energy relaxation rate. We examine the effect of resonant relaxation on the rate of tidal disruption of stars by the central mass; we find that the flux of stars into the loss cone is enhanced when the loss cone is empty, but that the disruption rate averaged over the entire cluster is not strongly affected. We show that relativistic precession can disable resonant relaxation near the main-sequence loss cone for black hole masses comparable to those in galactic nuclei. Resonant dynamical friction leads to growth or decay of the eccentricity of the orbit of a massive body, depending on whether the distribution function of the stars is predominantly radial or tangential. The accelerated relaxation implies that there are regions in nuclear star clusters that are relaxed in angular momentum but not in energy; unfortunately, these regions are not well-resolved in nearby galaxies by the Hubble Space Telescope.

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We report detections of three z ∼ 2.5 submillimeter-selected galaxies (SMGs; SMM J14011+0252, SMM J14009+0252, SMM J04431+0210) in the lowest rotational transition of the carbon monoxide molecule (CO J = 1 − 0) and one nondetection (SMM J04433+0210). For the three galaxies we detected, we find a line-integrated brightness temperature ratio of the J = 3 − 2 and 1 − 0 lines of 0.68±0.08; the 1−0 line is stronger than predicted by the frequent assumption of equal brightnesses in the two lines and by most single-component models. The observed ratio suggests that mass estimates for SMGs based on J = 3 − 2 observations and J = 1 − 0 column density or mass conversion factors are low by a factor of 1.5. Comparison of the 1 − 0 line intensities with intensities of higher-J transitions indicates that single-component models for the interstellar media in SMGs are incomplete. The small dispersion in the ratio, along with published detections of CO lines with J upper > 3 in most of the sources, indicates that the emission is from multi-component interstellar media with physical structures common to many classes of galaxies. This result tends to rule out the lowest scaling factors between CO luminosity and molecular gas mass, and further increases molecular mass estimates calibrated against observations of galaxies in the local universe. We also describe and demonstrate a statistically sound method for finding weak lines in broadband spectra that will find application in searches for molecular lines from sources at unknown redshifts.

We consider the e †ect of rapid rotation on the light curves of neutron stars with hot polar caps. For P B 3 ms spin periods, the pulse fractions can be as much as an order of magnitude larger than with simple, slowly rotating (Schwarzschild) estimates. Doppler boosting, in particular, leads to characteristic distortion and "" soft lags ÏÏ in the pulse proÐles, which are easily measurable in light curves with moderate energy resolution. With D105 photons it should also be possible to isolate the more subtle distortions of light travel time variations and frame dragging. Detailed analysis of high-quality millisecond pulsar data from upcoming X-ray missions must include these e †ects.