<p>If present, lithium is burned at lower temperatures than hydrogen (protium), although at higher temperatures than deuterium. See <a href="https://astronomy.stackexchange.com/questions/15119/why-does-lithium-fuse-at-lower-temperatures-than-hydrogen?rq=1">Why does lithium fuse at lower temperatures than hydrogen?</a></p>
<p>The primordial gas will contain lithium. It is created during big bang nucleosynthesis with an abundance of a bit less than 1 lithium nucleus for every billion protons.</p>
<p>Thus if temperatures reach (about) 3 million Kelvin, the lithium burns, but the much more abundant hydrogen (protium) and helium remains unignited.</p>

CC BY-SA 4.0
2023-11-29T15:57:38.550Z
2023-11-29T15:57:38.550Z
ProfRob
<p><a href="https://en.wikipedia.org/wiki/Lithium#Astronomical" rel="noreferrer">Lithium</a>, along with Hydrogen and Helium, was one of the 3 elements created in the Big Bang. Thus, it should exist to some part in any star that hasn't burnt all of it out, and as mentioned, it's not an easy thing to do. </p>

<p><a href="http://astronomy.swin.edu.au/cosmos/P/Population+III" rel="noreferrer">Population III</a> stars are expected to contain Lithium, and Beryllium as well. The amount, however, is not particularly high.</p>

CC BY-SA 3.0
2016-10-07T19:33:33.327Z
As far as I know, only trace amounts of lithium were produced by the Big Bang. Your source showing that it's in Population III stars is good though.
Sir Cumference
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2016-10-07T19:36:42.140Z
@SirCumference Hence why it is "energetically negligible". They're only pointing out that it *could* happen since the temperature is above the threshold and likely some non-zero amount of lithium exists.
zephyr
CC BY-SA 3.0
2016-10-07T19:38:04.283Z
@zephyr Ah, I assumed they called it "energetically negligible" simply because it doesn't produce nearly the amount of energy that the accretion disk does.
Sir Cumference
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2016-10-07T19:39:39.287Z
@SirCumference I'm sure both considerations are true.
zephyr
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2016-10-10T06:28:54.573Z
The primordial Li abundance is only a factor of 10 or so lower than that found in the interstellar medium today. Li is burned in population I star too, and it is also energetically negligible.
ProfRob
CC BY-SA 3.0
2016-10-10T16:58:14.813Z
@RobJeffries I knew and expected Population I stars could burn lithium, but I was surprised about Population III. However your point about lithium being relatively common clears that up.
Sir Cumference
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2016-10-07T19:30:33.323Z
2016-10-07T19:45:43.590Z
2016-10-07T19:45:43.590Z
PearsonArtPhoto
<p>According to <a href="http://mnras.oxfordjournals.org/content/387/4/1649.full.pdf" rel="nofollow">Begelman et al. (2008)</a>, one of the most distinguishing features of the hypothetical quasi-star is that it's supported by radiation pressure from the accretion disk of the black hole in its core. The paper suggests that these stars form from Population III stars.</p>

<p>What's more, while almost all of the star's luminosity is from the accretion disk (which is far more luminous than thermonuclear reactions), temperatures around the central black hole are hot enough for fusion:</p>

<blockquote>
  <p>Although we do not model the non-hydrostatic region of quasi-stars in any detail, in our case high temperatures <em>are</em> attained in the immediate vicinity of the black hole. However, even in this region the neglect of nuclear reactions is justified, first because black hole accretion is energetically much more efficient than fusion, and secondly because on-going accretion limits the time-scale over which inflowing gas is exposed to high $T$.</p>
</blockquote>

<p>That's all fine, but what surprised me is the footnote on the third page:</p>

<blockquote>
  <p>In the most massive quasi-stars, the central temperature may be high enough (a few million K) to initiate lithium burning. This is energetically negligible, and although the presence or absence of lithium does affect the opacity, the effect is small for the photospheric temperatures and densities of interest here.</p>
</blockquote>

<p>Even though this part dismisses lithium burning as an important factor, since it's energy output doesn't compare to that of the accretion disk's, it still mentions that lithium burning can take place. Considering that these form from Population III stars, how is it that much lithium burning can happen in the first place?</p>

<p>Although lithium is a relatively light atom, it is considered a metal and lithium burning depletes the amount of lithium in a star. Since Population III stars are supposed to be nearly metal-free, shouldn't only hydrogen or helium fusion be a factor here, even if they only have a small effect?</p>

CC BY-SA 3.0
2016-10-07T19:38:43.870Z
Interesting question, but it may be moot at this point. Recent work has shown these Pop III stars are likely to go supernova (or rather, hypernova given their masses) rather than form the seeds of SMBH as described in this paper. See [here](http://iopscience.iop.org/article/10.1088/0004-637X/790/2/162/meta) or [here](http://iopscience.iop.org/article/10.1088/0004-637X/775/2/107/meta) for example.
zephyr
CC BY-SA 3.0
2016-10-10T16:56:46.880Z
@zephyr That's quite a bummer :/
Sir Cumference
<black-hole><temperature><early-universe><metallicity><hypothetical>
How could lithium burning take place in a quasi-star?
Sir Cumference
# How could lithium burning take place in a quasi-star?

(Asked by: username_0 on 2016-10-07)

According to [Begelman et al. (2008)](http://mnras.oxfordjournals.org/content/387/4/1649.full.pdf), one of the most distinguishing features of the hypothetical quasi-star is that it's supported by radiation pressure from the accretion disk of the black hole in its core. The paper suggests that these stars form from Population III stars.

What's more, while almost all of the star's luminosity is from the accretion disk (which is far more luminous than thermonuclear reactions), temperatures around the central black hole are hot enough for fusion:

> Although we do not model the non-hydrostatic region of quasi-stars in any detail, in our case high temperatures *are* attained in the immediate vicinity of the black hole. However, even in this region the neglect of nuclear reactions is justified, first because black hole accretion is energetically much more efficient than fusion, and secondly because on-going accretion limits the time-scale over which inflowing gas is exposed to high $T$.

That's all fine, but what surprised me is the footnote on the third page:

> In the most massive quasi-stars, the central temperature may be high enough (a few million K) to initiate lithium burning. This is energetically negligible, and although the presence or absence of lithium does affect the opacity, the effect is small for the photospheric temperatures and densities of interest here.

Even though this part dismisses lithium burning as an important factor, since it's energy output doesn't compare to that of the accretion disk's, it still mentions that lithium burning can take place. Considering that these form from Population III stars, how is it that much lithium burning can happen in the first place?

Although lithium is a relatively light atom, it is considered a metal and lithium burning depletes the amount of lithium in a star. Since Population III stars are supposed to be nearly metal-free, shouldn't only hydrogen or helium fusion be a factor here, even if they only have a small effect?

**Tags:** black-hole, temperature, early-universe, metallicity, hypothetical

> **Comments:**
> **username_1**: Interesting question, but it may be moot at this point. Recent work has shown these Pop III stars are likely to go supernova (or rather, hypernova given their masses) rather than form the seeds of SMBH as described in this paper. See [here](http://iopscience.iop.org/article/10.1088/0004-637X/790/2/162/meta) or [here](http://iopscience.iop.org/article/10.1088/0004-637X/775/2/107/meta) for example.  
> **username_0**: @username_1 That's quite a bummer :/  

---

## 2 answers

### Answer by username_3 on 2016-10-07. Score: 6 | Accepted answer

[Lithium](https://en.wikipedia.org/wiki/Lithium#Astronomical), along with Hydrogen and Helium, was one of the 3 elements created in the Big Bang. Thus, it should exist to some part in any star that hasn't burnt all of it out, and as mentioned, it's not an easy thing to do.

[Population III](http://astronomy.swin.edu.au/cosmos/P/Population+III) stars are expected to contain Lithium, and Beryllium as well. The amount, however, is not particularly high.

> **Comments:**
> **username_0**: As far as I know, only trace amounts of lithium were produced by the Big Bang. Your source showing that it's in Population III stars is good though.  
> **username_1**: @username_0 Hence why it is "energetically negligible". They're only pointing out that it *could* happen since the temperature is above the threshold and likely some non-zero amount of lithium exists.  
> **username_0**: @username_1 Ah, I assumed they called it "energetically negligible" simply because it doesn't produce nearly the amount of energy that the accretion disk does.  
> **username_1**: @username_0 I'm sure both considerations are true.  
> **username_2**: The primordial Li abundance is only a factor of 10 or so lower than that found in the interstellar medium today. Li is burned in population I star too, and it is also energetically negligible.  
> **username_0**: @RobJeffries I knew and expected Population I stars could burn lithium, but I was surprised about Population III. However your point about lithium being relatively common clears that up.  

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### Answer by username_2 on 2023-11-29. Score: 3

If present, lithium is burned at lower temperatures than hydrogen (protium), although at higher temperatures than deuterium. See [Why does lithium fuse at lower temperatures than hydrogen?](https://astronomy.stackexchange.com/questions/15119/why-does-lithium-fuse-at-lower-temperatures-than-hydrogen?rq=1)

The primordial gas will contain lithium. It is created during big bang nucleosynthesis with an abundance of a bit less than 1 lithium nucleus for every billion protons.

Thus if temperatures reach (about) 3 million Kelvin, the lithium burns, but the much more abundant hydrogen (protium) and helium remains unignited.


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