Astronomy Colloquium

Wednesday, November 18, 2020
4:00pm to 5:00pm
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Online Event
Galactic seismology: the evolution of the "phase spiral" after the Sagittarius impact
Joss Bland-Hawthorn, Professor of Physics; Director, Sydney Institute for Astronomy, University of Sydney,

Our Galaxy, the Milky Way, is a benchmark for understanding disk galaxies. It is the only galaxy whose formation history can be studied using the full distribution of stars, from white dwarfs to supergiants. The oldest components provide unique insight into how galaxies form and evolve over billions of years. This is a veritable golden age for galactic archaeology with many large surveys now under way to map both chemistry and motions for stars in the Galaxy. Detailed 6D "phase space" information combined with chemistry for millions of stars heralds a new era in how we slice up the Galactic disc. This has already enabled the most remarkable discovery to emerge from ESA's Gaia satellite — the "phase spiral". This phenomenon, which was not foreseen, is direct evidence of giant waves crossing the disc. We discuss how the phase spiral is generated and what it may tell us about our history. We review the main science goals of Galactic seismology, and look to what the future may hold.  These studies will continue to play a fundamental role far into the future because there are measurements that can only be made in the near field and contemporary astrophysics depends on such observations.

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