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Theme of January 26 Cosmic Cocktail Hour is “Searching the Darkest Galaxies: Ultra-Faint Dwarfs as Dark Matter Laboratories”

Published on Jan 4, 2022

The left photo of Reticulum II shows mostly stars outside of this ultra-faint dwarf galaxy. The right photo of Reticulum II shows only stars that are within the galaxy that were identified using sophisticated image-search algorithms.

For the Carnegie Observatories Cosmic Cocktail Hour presented by the Pasadena Senior Center Wednesday, Jan. 26, at 4 p.m. via Zoom, Dr. Ethan Nadler will discuss the history of ultra-faint dwarf galaxies and describe how they provide unique tests of dark matter particle properties, followed by Q&A with viewers.

Illusive ultra-faint dwarf galaxies are dominated by the darkest matter and are the least luminous and least chemically evolved galaxies. Astronomers and astrophysicists perceive them as the best candidate fossils from the universe’s early stages. Reticulum II, for example, is a tiny, ultra-faint galaxy discovered in 2015 on the outskirts of our own Milky Way galaxy by astronomers who used the Dark Energy Survey’s panoramic survey telescope.

Dark matter cannot be seen directly because its particles do not absorb, reflect or emit light. The only way we know dark matter exists at all is the effect it has on objects astronomers can observe directly.

Nadler is a postdoctoral fellow at the Carnegie Observatories Theoretical Astrophysics Center in Pasadena. He researches near-field cosmology – the detailed study of the formation and evolution of nearby galaxies, including the Milky Way in which we live – as well as dark matter, the invisible material that makes up most of the universe. He is a member of the international Dark Energy Science Collaboration, which makes high-accuracy measurements of fundamental cosmological parameters using data from the Legacy Survey of Space and Time. He received his PhD in physics from Stanford University.

The cost of the monthly Cosmic Cocktail Hour is only $7 for members of the Pasadena Senior Center and $10 for nonmembers 50 and older. To register, visit and click on Lectures & Classes, then Cosmic Cocktail Hour or call 626-795-4331. Everyone who registers will receive an email link to access this Zoom event.

Then pour your favorite beverage, sit back and enjoy the astronomical trip.

In addition to online classes, onsite events and other activities, members and nonmembers of the Pasadena Senior Center are encouraged to visit the website regularly for a monthly magazine, COVID updates specifically for older adults and more.

The center, at 85 E. Holly St., is an independent, donor-supported nonprofit organization that has served older adults for more than 60 years. During the pandemic, doors are open Mondays through Fridays from 8:30 a.m. to 4:30 p.m. for social services and other critical services for older adults in need as well as limited occupancy for events, the library, fitness center and computer lab. Masks and social distancing are required. Rooms are sanitized after each use.

In accordance with Los Angeles County Public Health Department guidelines, proof of COVID vaccination is required for everyone who uses the fitness center or attends onsite activities indoors.

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