From Dr. Becky.
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
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👩🏽💻 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.
