<p>Yes. One of the most important open problems regarding supermassive black is their early formation. We have observed supermassive black holes at redshift <span class="math-container">$z&gt;6$</span>, when the universe was less than 1 billion years old. One example is  SDSS J0100+2802 (<a href="https://www.nature.com/articles/518490b" rel="nofollow noreferrer">Wu et al. 2015</a>), a black hole of <span class="math-container">$1.2 \times 10^{10} M_\odot$</span> at <span class="math-container">$z=6.3$</span>. We see these kind of SMBH in the form of quasars, i.e. we see the extremely bright light that is emitted by the matter infalling in the black hole. This means that these black holes are accreting a lot of mass, they are growing fast, so they must have started as much smaller black hole, but when did they form and how massive where their progenitors (usually called seeds)?</p>
<p>It turns out that there is a limit on how fast a black hole can accrete mass (<a href="https://en.wikipedia.org/wiki/Eddington_luminosity" rel="nofollow noreferrer">Eddington Limit</a>), so if they have reached <span class="math-container">$10^{10}M_\odot$</span> already before <span class="math-container">$z=6$</span>, they must either have started from already quite massive seeds or they must have started accreting very early in the history of the universe, before the formation of the first stars.</p>
<p>Primordial black holes could explain both scenarios, because they are thought to form at the time of inflation, so much less than one second after the big bang and they also could have a very wide range of mass, depending on who you ask. Therefore primordial black holes have been seriously considered as a possible source of super massive black hole seeds.</p>
<p><a href="https://arxiv.org/abs/astro-ph/0204486" rel="nofollow noreferrer">Could supermassive black holes be quintessential primordial black holes?</a></p>
<p><a href="https://arxiv.org/abs/1202.3848" rel="nofollow noreferrer">Primordial seeds of supermassive black holes</a></p>
<p><a href="https://arxiv.org/abs/1501.07565" rel="nofollow noreferrer">Massive Primordial Black Holes from Hybrid Inflation as Dark Matter and the seeds of Galaxies</a></p>

CC BY-SA 4.0
2022-06-20T08:54:50.810Z
2022-06-20T08:54:50.810Z
Prallax
<p>Prallax's answer deals with whether primordial black holes <em>could</em> be the seeds for supermassive black holes, and I have no argument with that answer. However, it doesn't deal with the second part of the question, or rather the statement - which is could those seeds, which would need to be <span class="math-container">$&gt;10^4M_\odot$</span> to make much difference to the &quot;Eddington accretion timescale problem&quot;, form all or a significant part of dark matter. The answer to that is currently thought to be NO.</p>
<p>The reasons are reviewed in section 6 of <a href="https://www.frontiersin.org/articles/10.3389/fspas.2021.681084/full" rel="nofollow noreferrer">Villanueva-Domingo et al. (2021)</a>, (see also <a href="https://arxiv.org/abs/2110.02821" rel="nofollow noreferrer">Carr &amp; Kuhnel 2022</a>), who show this plot - of the fraction of dark matter that could be in the form of primordial black holes, as a function of the black hole mass. Big swathes of black hole mass parameter space are ruled out as being significant contributors to dark matter by (i) microlensing observations that fail to find significant populations of <span class="math-container">$10^{-10}&lt; M/M_\odot &lt; 100$</span> compact objects in the halo of our Galaxy; (ii) the lack of evidence for perturbation of wide binary stars by a significant population of <span class="math-container">$&gt; 10^3 M_\odot$</span> black holes; (iii) accretion onto a significant population of primordial back holes would modify the CMB spectrum and its anisotropies.</p>
<p><a href="https://i.sstatic.net/Zb2tp.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Zb2tp.jpg" alt="Constraints on primordal black holes as dark matter" /></a></p>
<p><em>Constraints on primordial black holes as a fraction of the required dark matter. The shaded regions are ruled out by various labelled observational constraints.</em></p>
<p>The overall conclusion is that primordial black holes with masses <span class="math-container">$&gt;10^{-10}M_\odot$</span>  are not a major contributor to dark matter.</p>

CC BY-SA 4.0
2022-06-22T16:54:12.197Z
That's wonderful news. That means the black holes have about 1/10000 of an Earth mass.
Felicia
CC BY-SA 4.0
2022-06-22T20:15:02.107Z
@Felicia I don't follow your logic. The plot shows that primordial black holes with masses between $10^{17}$g and $10^{22}$g may still be significant contributors to dark matter. It doesn't show that they are. Such hypothetical objects have nothing to do with the growth of supermassive black holes.
ProfRob
CC BY-SA 4.0
2022-06-22T21:26:30.607Z
But is black holes with a mass bigger than 10exp-10 times of the Sun can't be a major contributor can holes with a smaller mass be a major part.
Felicia
CC BY-SA 4.0
2022-06-23T07:27:01.490Z
@Felicia that is exactly what I said. They could be.
ProfRob
CC BY-SA 4.0
2022-06-23T07:40:22.567Z
That's why I said it's wonderful news.
Felicia
CC BY-SA 4.0
2022-06-23T11:02:57.247Z
Why isn't it just assumed DM is black holes? Dark black holes. Occam's razor applies here.
Felicia
CC BY-SA 4.0
2022-06-20T16:20:30.097Z
2022-06-20T16:20:30.097Z
ProfRob
<p>If there were enough primordial black holes (with the right mass) they could explain dark matter. Could they explain the gargantuan monster holes in the center of galaxies?</p>

<black-hole><dark-matter><supermassive-black-hole><galactic-dynamics>
Could primordial black holes explain the SMBH in the galactic centers?
Felicia
# Could primordial black holes explain the SMBH in the galactic centers?

(Asked by: username_0 on 2022-06-19)

If there were enough primordial black holes (with the right mass) they could explain dark matter. Could they explain the gargantuan monster holes in the center of galaxies?

**Tags:** black-hole, dark-matter, supermassive-black-hole, galactic-dynamics


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## 2 answers

### Answer by username_1 on 2022-06-20. Score: 2

Yes. One of the most important open problems regarding supermassive black is their early formation. We have observed supermassive black holes at redshift $z>6$, when the universe was less than 1 billion years old. One example is SDSS J0100+2802 ([Wu et al. 2015](https://www.nature.com/articles/518490b)), a black hole of $1.2 \times 10^{10} M\_\odot$ at $z=6.3$. We see these kind of SMBH in the form of quasars, i.e. we see the extremely bright light that is emitted by the matter infalling in the black hole. This means that these black holes are accreting a lot of mass, they are growing fast, so they must have started as much smaller black hole, but when did they form and how massive where their progenitors (usually called seeds)?

It turns out that there is a limit on how fast a black hole can accrete mass ([Eddington Limit](https://en.wikipedia.org/wiki/Eddington_luminosity)), so if they have reached $10^{10}M\_\odot$ already before $z=6$, they must either have started from already quite massive seeds or they must have started accreting very early in the history of the universe, before the formation of the first stars.

Primordial black holes could explain both scenarios, because they are thought to form at the time of inflation, so much less than one second after the big bang and they also could have a very wide range of mass, depending on who you ask. Therefore primordial black holes have been seriously considered as a possible source of super massive black hole seeds.

[Could supermassive black holes be quintessential primordial black holes?](https://arxiv.org/abs/astro-ph/0204486)

[Primordial seeds of supermassive black holes](https://arxiv.org/abs/1202.3848)

[Massive Primordial Black Holes from Hybrid Inflation as Dark Matter and the seeds of Galaxies](https://arxiv.org/abs/1501.07565)


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### Answer by username_2 on 2022-06-20. Score: 1

username_1's answer deals with whether primordial black holes *could* be the seeds for supermassive black holes, and I have no argument with that answer. However, it doesn't deal with the second part of the question, or rather the statement - which is could those seeds, which would need to be $>10^4M\_\odot$ to make much difference to the "Eddington accretion timescale problem", form all or a significant part of dark matter. The answer to that is currently thought to be NO.

The reasons are reviewed in section 6 of [Villanueva-Domingo et al. (2021)](https://www.frontiersin.org/articles/10.3389/fspas.2021.681084/full), (see also [Carr & Kuhnel 2022](https://arxiv.org/abs/2110.02821)), who show this plot - of the fraction of dark matter that could be in the form of primordial black holes, as a function of the black hole mass. Big swathes of black hole mass parameter space are ruled out as being significant contributors to dark matter by (i) microlensing observations that fail to find significant populations of $10^{-10}< M/M\_\odot < 100$ compact objects in the halo of our Galaxy; (ii) the lack of evidence for perturbation of wide binary stars by a significant population of $> 10^3 M\_\odot$ black holes; (iii) accretion onto a significant population of primordial back holes would modify the CMB spectrum and its anisotropies.

[![Constraints on primordal black holes as dark matter](https://i.sstatic.net/Zb2tp.jpg)](https://i.sstatic.net/Zb2tp.jpg)

*Constraints on primordial black holes as a fraction of the required dark matter. The shaded regions are ruled out by various labelled observational constraints.*

The overall conclusion is that primordial black holes with masses $>10^{-10}M\_\odot$ are not a major contributor to dark matter.

> **Comments:**
> **username_0**: That's wonderful news. That means the black holes have about 1/10000 of an Earth mass.  
> **username_2**: @username_0 I don't follow your logic. The plot shows that primordial black holes with masses between $10^{17}$g and $10^{22}$g may still be significant contributors to dark matter. It doesn't show that they are. Such hypothetical objects have nothing to do with the growth of supermassive black holes.  
> **username_0**: But is black holes with a mass bigger than 10exp-10 times of the Sun can't be a major contributor can holes with a smaller mass be a major part.  
> **username_2**: @username_0 that is exactly what I said. They could be.  
> **username_0**: That's why I said it's wonderful news.  
> **username_0**: Why isn't it just assumed DM is black holes? Dark black holes. Occam's razor applies here.  

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