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Workshop / Seminar

Colloquium: Physics & Astronomy – Guy Worthey

Webster Physical Science Building, Pullman, WA 99163
Room 17
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About the event

The Department of Physics and Astronomy invites all to a colloquium featuring Dr. Guy Worthey, Department of Physics and Astronomy. Dr. Guy Worthey will present their talk, “Galaxy Assembly.”

Meet for refreshments before the lecture at 3:45 – 4:10 p.m. in the foyer on floor G above the lecture hall.


I review the state of understanding in galaxy evolution. After the big bang, a cooling, expanding universe of neutral hydrogen and helium experienced localized gravitational instabilities. The overdense regions coalesced, eventually forming galaxies and clusters of galaxies. Matter became locked into stars, the universe reionized, and chemical evolution began as a consequence of thermonuclear processing inside stars.

Dark matter probably comprises 85% of the matter in the universe and therefore dominated the initial linear graviational instability of the universe. But dark matter cannot dissipate energy, and baryonic matter may therefore drive the evolution during the nonlinear phases of collapse. Collapse is assumed to occur hierarchically, with smaller subunits merging with other subunits to form larger ones. Galaxies span seven orders of magnitude in mass. Above that mass, galaxy clusters of up to thousands of galaxies segue to filamentary superclusters of hundreds of clusters.

Split by position in the mass hierarchy, the question of timing is an area of ongoing debate. Lookback studies give clues, and age measurements in nearby galaxies give complimentary clues, and sometimes the clues are not in accord. In the near future, James Webb Space Telescope will increase the power of lookback studies, while a new technique of age-dating starlight promises a more detailed unravelling of nearby fossil (galaxies).



Physics and Astronomy