September 13: Fossils of Formation

On Friday, September 13th, we launched our 2013 Fall Public Lecture & Stargazing series with a talk on the Milky Way. Post-doctoral researcher, Allyson Sheffield, presented what we currently know about the formation of our galaxy. It turns out that galaxies formed in a hierarchical manner after the Big Bang, with small clumps of gas and dust forming stars, then clusters of stars, and eventually protogalaxies and galaxies. In essence, all galaxies form by accreting other galaxies in a process called galactic cannibalism. Allyson's work deals with observing tidal streams surrounding our galaxy and tracing them back in time and space to determine what structures they originally came from. She is currently focusing her efforts on the Triangulum-Andromeda over-density.

After the lecture, many visitors headed to the roof for some clear sky observing of the Moon, Mizar and Alcor, Alberio, and the Ring Nebula while others remained in the lecture hall to hear about the recent news of the Voyager 1 probe entering interstellar space.

Friday's volunteers included graduate students Jinjing Chen in the lecture hall, Adrian Price-Whelen, Susan Clark, Steven Mohammed, Doug Thornhill, and Yuan Li on the roof, and undergraduates Gladys Velez-Caicedo and Varad Srinivasan on the 3D Wall.

Join us for our next event on Friday, Sept. 27th to hear more on Voyager 1!

--Summer Ash, Director of Outreach

November 30: Galactic Neighborhoods

On November 30th, about 100 people joined us to hear Columbia Astronomy Professor Jacqueline van Gorkom talk about how galaxies are influenced by their surroundings. Professor van Gorkom is a radio astronomer and does extensive research on galaxies. She showed us how strikingly different galaxies look in dense clusters of galaxies compared with fields. She explained that when a galaxy enters a galaxy cluster filled with hot intra-cluster gas, the cold gas inside the galaxy gets stripped out of it and thus star formation is quenched, which changes the color of the galaxy from blue to red. The audience raised a lot of interesting questions about galaxies and gravity.

After the talk, some people went to see the 3D movies on the 13th floor shown by Columbia undergraduate student Gladys Velez-Caicedo. Unfortunately, the sky was not clear on Friday, but Columbia Astronomy graduate students Adrian Price-Whelan and Jenna Lemonias gave a telescope tour to a group of people on the roof of Pupin. In the lecture hall, graduate student Yuan Li presented a slide show on spiral galaxies and Dr. Jana Grcevich talked about the Big Bang and the expansion of the universe.

Join us on December 14th for the last event of this semester: a panel discussion on Life, the Universe, and Everything!

--Yuan

February 11, 2010: Galactic Sleuthing Lecture and Public Observing

This past Friday, Dr. Allyson Sheffield, a current post-doc of the Columbia Astronomy department, gave a talk entitled, ''Galactic Sleuthing: Unraveling the Milky Way’s Past.'' In her talk, Allyson described two prevailing models for galactic formation. First, 'monolithic collapse' posits that a galactic-sized gas reservoir (of Hydrogen and Helium) collapses all at once, creating an old population halo of stars first and then flattens out into a disk composed of younger stars. Second, she presented the theory of 'hierarchical merging' that posits that galaxies are built up from the accretion of smaller galaxies and the merging of bigger ones.

Allyson then talked about how we can determine which scenario better describes the evolutionary path of our own galaxy by looking at both the group motions of stars and their shared chemical abundances. By showing us data and simulations by Rodrigo Ibata and his collaborators and by our very own Prof. Kathryn Johnston, respectively, she showed us how the merging Sagittarius dwarf galaxy was discovered by surveying stellar velocities in the galaxy along with models that describe how the dwarf galaxy would currently look which were later confirmed by additional chemical abundance observations.

Finally, she showed us how one can merge the two indicators of common ancestry to look at moving groups closer to us and determine if evidence for other accreted dwarf galaxy remnants remain in the galaxy by looking at the spectra of stars with similar peculiar velocities. She found that she could likely link certain groups to larger ones seen in the galactic halo stellar streams by models that would predict the location of these peculiar stars. Given her research and the other research she presented, we learned that merging plays a significant role in galaxy evolution and that one can recount this evolution based on remnants of past accretion events.

We had a great turn out and our attendees made full use of our facilities by watching astronomy visualizations on our 3-D wall, ran by graduate student Jana Grcevich, and by going to the roof to stargaze. It's cool to think that many of the stars we observed, including our own, exhibit group origins or movements that were probably even more defined in the past.

Thanks to the 8 volunteers and the 130 people who attended our lecture and observing night!