Right after lunch today, Ben Farr (Oregon) gave a seminar about how gravitational waves are detected by LIGO from a data-analysis perspective. He has been a big part of the team that made the LIGO results so probabilistically righteous! He gave some credit to the injection tests in the system for demonstrating that the Bayesian techniques were the highest-performing methods. He showed results on black-hole spins: He finds that either spins are low in amplitude, or else they tend to be aligned with one another and the orbital plane. That's already a fairly substantial result with 6-ish systems; and there will be many more soon. After his talk we discussed noise modeling.

Late in the day, I had a phone call with Ana Bonaca (Harvard) to discuss next steps after her beautiful paper on GD-1 in Gaia. I pitched a method for simulating dark-matter-subhalo interactions with streams that Kathryn Johnston (Columbia) and I worked out many years ago. We discussed how to make simulations that are realistic enough to be useful now.

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