Astrotagging and Milky Way orbits

I attended an excellent talk today by David Hogg, a cosmologist at NYU, that was titled “A Comprehensive Model of All Astronomical Imaging Ever Taken.” Here I highlight just two of the interesting and thought-provoking topics that appeared in his talk.

Astrotagging: His group developed, a service that will analyze digital images of the night sky and automatically annotate them with identifiable stars. You can access this impressive service by uploading a photo to flickr and adding it to the group “astrometry,” as in this example. Automatically, analyzes all new images added to this group and adds a comment with all of the stars that were found, as well as marking them on the image itself. Clever, reliable, and useful! Nice work!

Milky Way orbits: Kepler deduced planetary orbits based on repeated observations of planetary positions. We know that our Sun, and the rest of the stars in our galaxy, also orbit around the Milky Way’s core. But those orbits are perturbed by the presence of dark matter, something we can’t observe directly, and anyway, it would take hundreds of millions of years just to observe one orbit. Could there be a short cut? If you look up at the sky in the right location you can find a “stream” of stars that mark out one such orbital tracks, where clumps of stars formed together but moved slightly apart, along their shared orbit. Hogg and colleagues came up with a 6-D description of an orbit fit to those observations, concluding that the best fit is “an eccentric orbit in a flattened isothermal potential.” For more details, see their paper: “Constraining the Milky Way Potential with a Six-Dimensional Phase-Space Map of the GD-1 Stellar Stream”. I wonder what this line of inquiry will end up telling us about that dark matter distribution?

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