Uploaded February 2026 | Updated September 2026, 2 weeks ago
AD - To try everything Brilliant has to offer for free for 30 days visit brilliant.org/DrBecky and you'll also get 20% off an annual premium subscription which gives you unlimited daily access to Brilliant. | How many galaxies are there out there in the Universe? Well our best estimate in 2026 is that there’s *at least* 2 trillion galaxies, islands of billions of stars just like our own Milky Way galaxy. But how do we actually know that? That’s far too big of a number for anyone to have gone out and literally done a count one by one [insert home alone count scene], so what do we do instead? Well in this video we’re going to dive in to how us astrophysicists get at this number, and we’re going to try and put that number into content, how big is 2 trillion really?
Conselice et al. (2016) - assets.science.nasa.gov/content/dam/science/missions/hubble/releases/2016/10/STScI-01EVSR313NHNAC17DF62MP9QV9.pdf
00:00 2 TRILLION galaxies
01:10 Complication 1: the observable Universe
02:40 Complication 2: which direction you look in?
04:31 Complication 3: which telescope you use
06:35 Complication 4: what counts as a galaxy?
08:31 How big is 2 trillion really?
Video filmed on a Sony ⍺7 IV
Video edited by Martino Gasparrini: fiverr.com/mgs_editing
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📚 My book, "A Brief History of Black Holes", out NOW in hardback, paperback, e-book and audiobook (which I narrated myself!): lnk.to/DrBecky
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👕 My merch, including JWST designs, are available here (with worldwide shipping!): dr-becky.teemill.com
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🎧 Royal Astronomical Society Podcast that I co-host: podfollow.com/supermassive
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🔔 Don't forget to subscribe and click the little bell icon to be notified when I post a new video!
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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.
drbecky.uk.com
AD - To try everything Brilliant has to offer for free for 30 days visit brilliant.org/DrBecky and you'll also get 20% off an annual premium subscription which gives you unlimited daily access to Brilliant. | How many galaxies are there out there in the Universe? Well our best estimate in 2026 is that there’s *at least* 2 trillion galaxies, islands of billions of stars just like our own Milky Way galaxy. But how do we actually know that? That’s far too big of a number for anyone to have gone out and literally done a count one by one [insert home alone count scene], so what do we do instead? Well in this video we’re going to dive in to how us astrophysicists get at this number, and we’re going to try and put that number into content, how big is 2 trillion really?
Conselice et al. (2016) - assets.science.nasa.gov/content/dam/science/missions/hubble/releases/2016/10/STScI-01EVSR313NHNAC17DF62MP9QV9.pdf
00:00 2 TRILLION galaxies
01:10 Complication 1: the observable Universe
02:40 Complication 2: which direction you look in?
04:31 Complication 3: which telescope you use
06:35 Complication 4: what counts as a galaxy?
08:31 How big is 2 trillion really?
Video filmed on a Sony ⍺7 IV
Video edited by Martino Gasparrini: fiverr.com/mgs_editing
---
📚 My book, "A Brief History of Black Holes", out NOW in hardback, paperback, e-book and audiobook (which I narrated myself!): lnk.to/DrBecky
---
👕 My merch, including JWST designs, are available here (with worldwide shipping!): 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.
drbecky.uk.com
