A star so close to the Milky Way’s black hole it feels its spin
From Dr. Becky.
Watch this video on YouTube ↗
We thought this was the closest star to the black hole at the centre of the Milky Way, turns out we were wrong! It’s actually this one, S301. It’s 2 billion times fainter than the brightest stars in the night sky, it comes closer to the black hole at the centre than Uranus does to the Sun, travelling at 25,000 km/s - that’s 8% of the speed of light!
But it’s not getting torn apart, or sucked in. It’s on a stable orbit. And that is really, really good news for us astrophysicists. Because with this star we should be able to directly measure how fast the Milky Way’s black hole is spinning for the first time.
Because: mass, spin, and charge, those are the only three properties that black holes have. And we’ve only ever directly measured one of them for the black hole at the centre of the Milky Way.
But all that is about to change...
But why do we even care about spin? Well that’s something we’re going to dive into in this video, along with how we measure black hole spin including directly through the Lense Thirring effect, and how this newly discovered star holds the key to doing just that.
Papers mentioned:
GRAVITY collaboration (2026) - https://arxiv.org/pdf/2607.12664
Beckmann et al. (2024) - https://arxiv.org/pdf/2211.13614
Fabian et al. (2002) - https://arxiv.org/pdf/astro-ph/0206095
Reynolds & Fabian (2007) - https://arxiv.org/pdf/0711.4158
Smethurst et al. (2019) - https://arxiv.org/pdf/1909.01355
Smethurst et al. (2021) - https://arxiv.org/pdf/2108.05361
00:00 - Introduction
01:32 - I - Why we care about black hole spin
05:31 - II - How we measure black hole spin and the Lense-Thirring effect
10:24 - III - The newly discovered S301, the closest star to the Milky Way's black hole
15:44 - Bloopers
Video filmed on a Sony ⍺7 IV
Video edited by Martino Gasparrini: martino.freelance@gmail.com
Video produced by Marina Hui & Dr Becky Smethurst
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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!): http://lnk.to/DrBecky
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👕 My merch, including JWST designs, are available here (with worldwide shipping!): https://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!
---
👩🏽💻 I'm Dr. Becky Smethurst, an astrophysicist at the University of Oxford. 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
But it’s not getting torn apart, or sucked in. It’s on a stable orbit. And that is really, really good news for us astrophysicists. Because with this star we should be able to directly measure how fast the Milky Way’s black hole is spinning for the first time.
Because: mass, spin, and charge, those are the only three properties that black holes have. And we’ve only ever directly measured one of them for the black hole at the centre of the Milky Way.
But all that is about to change...
But why do we even care about spin? Well that’s something we’re going to dive into in this video, along with how we measure black hole spin including directly through the Lense Thirring effect, and how this newly discovered star holds the key to doing just that.
Papers mentioned:
GRAVITY collaboration (2026) - https://arxiv.org/pdf/2607.12664
Beckmann et al. (2024) - https://arxiv.org/pdf/2211.13614
Fabian et al. (2002) - https://arxiv.org/pdf/astro-ph/0206095
Reynolds & Fabian (2007) - https://arxiv.org/pdf/0711.4158
Smethurst et al. (2019) - https://arxiv.org/pdf/1909.01355
Smethurst et al. (2021) - https://arxiv.org/pdf/2108.05361
00:00 - Introduction
01:32 - I - Why we care about black hole spin
05:31 - II - How we measure black hole spin and the Lense-Thirring effect
10:24 - III - The newly discovered S301, the closest star to the Milky Way's black hole
15:44 - Bloopers
Video filmed on a Sony ⍺7 IV
Video edited by Martino Gasparrini: martino.freelance@gmail.com
Video produced by Marina Hui & Dr Becky Smethurst
---
📚 My 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 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. 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
