<p>As mentioned in the comments, your question kind of has two parts.</p>
<p>First are M stars. These are proper stars, having hydrogen fusion, and are actually quite terrible for any kind of life. The reason for this is the incredibly intense magnetic fields and fully convective nature of these stars. The dynamo effect (moving charged liquids creating magnetic fields) is largely to blame here, and is especially bad since from surface to core you have full convection (whereas in larger stars, you have confection regions of smaller fractions of the star). These magnetic fields lead to terrible, terrible stellar weather that would likely wipe out any living thing, <em>especially</em> given the fact that a planet would have to be so close to be in the Goldilocks zone.</p>
<p>Next are the L, T and Y ‘stars’. These objects are brown dwarfs, but brown dwarf specialists often still refer to them as stars, and rightfully so to an extent; brown dwarfs still have fusion happening in them, but not hydrogen fusion, mostly deuterium and sometimes lithium fusion. This isn’t enough to keep the brown dwarf at a stable temperature, however, and so brown dwarfs progressively cool down throughout their lifetime. They can get pretty cold in comparison to hydrogen fusing stars, and so the habitable zone will change over time, making the zones much less Goldilocks than we’d like for anything to realistically survive. Below is a visual that shows much better than I could say exactly how it evolves. Credit to Bolmont et al. for the data, and this website for the visualization :</p>
<p><a href="https://planetplanet.net/2014/10/09/real-life-sci-fi-world-4-earth-around-a-brown-dwarf/" rel="nofollow noreferrer">https://planetplanet.net/2014/10/09/real-life-sci-fi-world-4-earth-around-a-brown-dwarf/</a></p>
<p><img src="https://planetplanetdotnet.files.wordpress.com/2014/10/bd_hz_labels-001.jpg" alt="Habitable Zone for Brown dwarfs" /></p>

CC BY-SA 4.0
2021-12-03T21:43:20.743Z
Some L-stars are stars and some M stars are brown dwarfs. Depends on their age.
ProfRob
CC BY-SA 4.0
2021-12-04T00:08:33.330Z
True, will edit to reflect that.
Justin T
CC BY-SA 4.0
2021-12-03T08:33:12.097Z
2021-12-03T08:38:43.823Z
2021-12-03T08:38:43.823Z
Justin T
<p>Ignoring <a href="https://en.wikipedia.org/wiki/Tidal_heating" rel="noreferrer">tidal heating</a> and such, how can one calculate the <a href="https://en.wikipedia.org/wiki/Circumstellar_habitable_zone" rel="noreferrer">habitable orbital ranges</a> for  M, L, T, and Y <a href="https://en.wikipedia.org/wiki/Stellar_classification" rel="noreferrer">spectral class</a> stars?</p>
<p>The reason I ask is that I'm also curious if any of these zones encroach on their respective Roche limits.</p>

CC BY-SA 4.0
2021-12-01T21:57:14.427Z
I've edited your question to include some links and to make the question more interesting to answer by ask "How to calculate...?" rather than just "What's the answer?" And I think your question about the Roche limit is *so compelling* that it should be included in the question itself!
uhoh
CC BY-SA 4.0
2021-12-02T18:44:48.377Z
Brown dwarfs are not stars, any moe than they are planets or planetary mass objectsi.  They are a different catebory of objects intermediate between planets and stars, with somewhat vague borders.  But I upvoted the question because the answers would be interesting.
M. A. Golding
CC BY-SA 4.0
2021-12-03T00:01:58.937Z
@M.A.Golding I didn't know that!  Wikipedia's article *Stellar classification* includes them so it's easy to think naively that they are kinds of stars. So I guess neutron stars are not stars either? Related to the issue of vague borders: [Do astronomers generally agree that the distinction between comets and asteroids is not so clear?](https://astronomy.stackexchange.com/q/19963/7982)
uhoh
<habitable-zone>
How to calculate the goldilocks zones of brown dwarf stars? Do any encroach on the stars' Roche limit?
H2Forge
# How to calculate the goldilocks zones of brown dwarf stars? Do any encroach on the stars' Roche limit?

(Asked by: username_0 on 2021-12-01)

Ignoring [tidal heating](https://en.wikipedia.org/wiki/Tidal_heating) and such, how can one calculate the [habitable orbital ranges](https://en.wikipedia.org/wiki/Circumstellar_habitable_zone) for M, L, T, and Y [spectral class](https://en.wikipedia.org/wiki/Stellar_classification) stars?

The reason I ask is that I'm also curious if any of these zones encroach on their respective Roche limits.

**Tags:** habitable-zone

> **Comments:**
> **username_1**: I've edited your question to include some links and to make the question more interesting to answer by ask "How to calculate...?" rather than just "What's the answer?" And I think your question about the Roche limit is *so compelling* that it should be included in the question itself!  
> **username_2**: Brown dwarfs are not stars, any moe than they are planets or planetary mass objectsi.  They are a different catebory of objects intermediate between planets and stars, with somewhat vague borders.  But I upvoted the question because the answers would be interesting.  
> **username_1**: @username_2 I didn't know that!  Wikipedia's article *Stellar classification* includes them so it's easy to think naively that they are kinds of stars. So I guess neutron stars are not stars either? Related to the issue of vague borders: [Do astronomers generally agree that the distinction between comets and asteroids is not so clear?](https://astronomy.stackexchange.com/q/19963/7982)  

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## 1 answers

### Answer by username_3 on 2021-12-03. Score: 2

As mentioned in the comments, your question kind of has two parts.

First are M stars. These are proper stars, having hydrogen fusion, and are actually quite terrible for any kind of life. The reason for this is the incredibly intense magnetic fields and fully convective nature of these stars. The dynamo effect (moving charged liquids creating magnetic fields) is largely to blame here, and is especially bad since from surface to core you have full convection (whereas in larger stars, you have confection regions of smaller fractions of the star). These magnetic fields lead to terrible, terrible stellar weather that would likely wipe out any living thing, *especially* given the fact that a planet would have to be so close to be in the Goldilocks zone.

Next are the L, T and Y ‘stars’. These objects are brown dwarfs, but brown dwarf specialists often still refer to them as stars, and rightfully so to an extent; brown dwarfs still have fusion happening in them, but not hydrogen fusion, mostly deuterium and sometimes lithium fusion. This isn’t enough to keep the brown dwarf at a stable temperature, however, and so brown dwarfs progressively cool down throughout their lifetime. They can get pretty cold in comparison to hydrogen fusing stars, and so the habitable zone will change over time, making the zones much less Goldilocks than we’d like for anything to realistically survive. Below is a visual that shows much better than I could say exactly how it evolves. Credit to Bolmont et al. for the data, and this website for the visualization :

<https://planetplanet.net/2014/10/09/real-life-sci-fi-world-4-earth-around-a-brown-dwarf/>

![Habitable Zone for Brown dwarfs](https://planetplanetdotnet.files.wordpress.com/2014/10/bd_hz_labels-001.jpg)

> **Comments:**
> **username_4**: Some L-stars are stars and some M stars are brown dwarfs. Depends on their age.  
> **username_3**: True, will edit to reflect that.  

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