Caltech Astronomy Public Lecture Series - Galaxy Clusters Collide: The Most Energetic Events since the Big Bang - Emily Silich - 08/25/2023

Galaxy clusters are collections of hundreds of galaxies, the largest and most massive structures in the universe. But what happens when two galaxy clusters collide, and what does it tell us about the nature of matter itself? Join us for a 30-minute lecture, followed by a panel Q&A consisting of several astrophysicists to answer your questions about astronomy, astrophysics, and space science. Timestamps below: 00:00 Announcements 05:32 Intro to Galaxy Cluster Presentation 06:12 Galaxy Cluster Presentation 31:35 Q&A for Galaxy Cluster Presentation 31:51 "Does the cluster collision change the galaxies themselves?" 33:19 "How is gravitational lensing measured?" 36:18 "Do galaxy clusters generate other wavelengths of light?" 37:39 "Why does the galaxy cluster center have so much dark matter?" 39:51 "What is dark matter made of?" 42:00 Intermission 46:19 Q&A Panel Introductions 50:10 "Are there galaxies that do not belong to a cluster?" 51:05 "Are individual galaxies reshaped during a cluster collsion?" 53:41 "When galaxies collide, do they form new stars?" 56:26 "Is our Local Group considered a galaxy cluster?" 57:55 "How frequent are galaxy cluster collisions?" 59:01 "Are galaxy clusters the largest structures in the universe?" 1:00:35 "What is the life of a galaxy cluster?" 1:01:32 "Is computer science related to astronomy?" 1:05:39 "Did JWST discover something that upended our theories?" 1:11:15 "How does the expansion of the universe affect galaxy clusters?" 1:12:28 "When did the panelists become interested in astronomy as a career?" 1:18:06 "Does visible matter dominate over dark matter in certain environments?" 1:22:10 "Why doesn't dark matter behave like regular matter?" 1:24:50 "Does dark matter interact with itself?" 1:27:10 "Is there a dark universe of dark matter around us that we cannot see?" 1:29:13 "Do the panelists recommend early decision for college?" 1:33:21 "Could dark matter be neutrinos?" 1:37:20 "Can the expanding universe tear apart galaxy clusters? (part one)" 1:40:35 "How do computational simulations actually work?" 1:45:48 "Can the expanding universe tear apart galaxy clusters? (part two)" 1:51:45 "What is the multiverse?" 1:56:19 Concluding Remarks Title: Galaxy Clusters Collide: The Most Energetic Events since the Big Bang Speaker: Emily Silich Abstract: Galaxies, like our own Milky Way, don’t tend to live in isolation. When we scan our telescopes across the sky, we don’t see a random scattering of galaxies throughout space. Instead, we see many dense regions where hundreds to thousands of galaxies exist in close proximity to each other, known as galaxy clusters. These clusters, surrounded by dark matter and extremely hot gas, are the largest and most massive objects in the universe bound together by their own gravity. So, what happens when two of these galaxy clusters collide? Some of the most energetic events in the universe — second only to the Big Bang itself! I’ll discuss how studying these powerful collisions can answer exciting questions, from how structures in the universe form to the nature of dark matter itself.