stars at low resolution, pair coding, accretion

Today Kathryn Johnston (Columbia) convened the first of (we hope) many Local-Group group meetings up at Columbia, with people present from NYU, CCA, Columbia, and Princeton. Johnston reported on things she learned at the recent meeting in Paris. Of particular interest to her—and everyone, apparently—was work by Yuan-Sen Ting (Harvard), building on experiments by Anna Y. Q. Ho (Caltech), showing that it is possible to get detailed stellar abundances, even without huge covariances, out of low-resolution spectra. The point is that as resolution decreases, the information per line gets worse, but you also (usually) get more spectral coverage, and this (mostly) compensates. This could have a huge impact on the future of stellar astrophysics.

I spent time today pair-coding (with Adrian Price-Whelan, Princeton) the analytic marginalized likelihood that Semyeong Oh (Princeton) and Price-Whelan and I have been working on. We found a couple bugs and by the end of the screen-sharing video call (yes, that's the way we do it), we had a marginalized likelihood ratio that seems to be delivering very good answers, and fast! Very excited.

The research day ended with a great astrophysics seminar at NYU by Zoltan Haiman (Columbia, NYU) about fast growth of black holes in the early Universe. He has found a spherically symmetric, steady-state, achievable accretion process that is (much) faster than Eddington, using the same assumptions (essentially). I need to think about it and understand it better. The Eddington limit is one of the most secure, robust, and well-tested arguments in all of astrophysics!

1 comment:

  1. I don't know what Zoltan had in mind, but there are at least 2 easy ways around the "Eddington Limit" —
    One is if the infalling matter converts its energy to heat below the event horizon (i.e., if it's on a nearly radial orbit).
    The other is if the photons created are in an optically thick region and there's more infalling matter on top — the photons can be advected backward with the flow and carried below the event horizon.