We Can't Explain Spiral Galaxies - The Winding Problem

Video Description

To try everything Brilliant has to offer for free for a full 30 days, visit https://brilliant.org/DrBecky and you'll also get 20% off an annual premium subscription - AD | Wherever we look in the Universe we see spiral galaxies. 70% of all galaxies today have this spiral structure that show up in their stars and their gas that’s used to make more stars. And in my opinion they are the most beautiful object in the entire Universe - you can get completely lost following the spirals around in some galaxies - but can we explain how those spiral shapes form in galaxies? NOPE. There is still no consensus amongst us astrophysicists for how these spiral arms in galaxies form. And that’s thanks in part due to the huge amount of variation you see in galaxies with spirals. There’s ones with 2 spirals, 3 spirals, 4 spirals, ones that are so fluffy you can’t even count the number of spirals, there’s ones with bars running through the middle where the spirals come off the ends of the bars, or ones with bars where the spirals don’t attach to the bars, there’s loose spirals, tight spirals, big stretched out tidal spirals, there’s blue spirals, and red spirals, spirals in pairs and spirals by themselves, and galaxies that look like they should have spirals, but don’t. Explaining all of that variation is no small feat, and while we have a number of ideas on how spirals could form in galaxies, and why some have them and others don’t, we still don’t fully understand them... Athanassoula (1984 - behind paywall) - https://doi.org/10.1016/0370-1573(84)90156-X Block et al. (1994) - https://articles.adsabs.harvard.edu/pdf/1994A%26A...288..365B Block & Wainscoat (1991 - behind paywall) - https://www.nature.com/articles/353048a0 Fujii et al. (2011) - https://arxiv.org/pdf/1006.1228 Gerola & Seiden (1978) - https://articles.adsabs.harvard.edu/pdf/1978ApJ...223..129G Goldreich & Lynden-Bell (1965) - https://articles.adsabs.harvard.edu/pdf/1965MNRAS.130..125G González & Graham (1996) - https://articles.adsabs.harvard.edu/pdf/1996ApJ...460..651G Lin & Shu (1964) - https://articles.adsabs.harvard.edu/pdf/1964ApJ...140..646L Martínez-García et al. (2023) - https://arxiv.org/pdf/2306.08037 Martínez-García et al. (2009) - https://arxiv.org/pdf/0812.3647 Miller et al. (2019) - https://arxiv.org/pdf/1907.09390 Mueller & Arnett (1976) - https://articles.adsabs.harvard.edu/pdf/1976ApJ...210..670M Oort (1927) - https://articles.adsabs.harvard.edu/pdf/1927BAN.....3..275O Rubin & Ford (1970) - https://articles.adsabs.harvard.edu/pdf/1970ApJ...159..379R Thornley (1996) - https://articles.adsabs.harvard.edu/pdf/1996ApJ...469L..45T Toomre (1981) - https://articles.adsabs.harvard.edu/pdf/1981seng.proc..111T For some recent review articles on spiral galaxy structure see: Shu (2016) - https://www.annualreviews.org/content/journals/10.1146/annurev-astro-081915-023426 Sellwood & Masters (2022) - https://www.annualreviews.org/content/journals/10.1146/annurev-astro-052920-104505 00:00 Introduction 03:16 The discovery of spiral galaxies and the winding problem 07:29 Density wave theory 08:57 Stochastic Self Propagating star formation (SSPSF) 10:39 Swing amplification theory 12:49 Why none of these ideas explain spiral structure fully 19:44 Bloopers Video filmed on a Sony ⍺7 IV Video edited by Martino Gasparrini: https://www.fiverr.com/mgs_editing --- 📚 My new book, "A Brief History of Black Holes", out NOW in hardback, paperback, e-book and audiobook (which I narrated myself!): http://lnk.to/DrBecky --- 👕 My new merch, including JWST designs, are available here (with worldwide shipping!): https://dr-becky.teemill.com/ --- 🎧 Royal Astronomical Society Podcast that I co-host: podfollow.com/supermassive --- 🔔 Don't forget to subscribe and click the little bell icon to be notified when I post a new video! --- 👩🏽‍💻 I'm Dr. Becky Smethurst, an astrophysicist at the University of Oxford (Christ Church). I love making videos about science with an unnatural level of enthusiasm. I like to focus on how we know things, not just what we know. And especially, the things we still don't know. If you've ever wondered about something in space and couldn't find an answer online - you can ask me! My day job is to do research into how supermassive black holes can affect the galaxies that they live in. In particular, I look at whether the energy output from the disk of material orbiting around a growing supermassive black hole can stop a galaxy from forming stars. http://drbecky.uk.com