<p>Some people certainly think that primordial black holes could account for a significant fraction of dark matter and at least provide the seeds for growing supermassive black holes in the early universe.</p>
<p>One of the the most pressing puzzles in cosmology and the study of early galaxies is how you can find quasars which have inferred central black hole masses of a billion times that of the Sun (or more) in existence just a few hundred million years after the big bang. There are a number of suggested solutions, but one of these is indeed that <em>primordial</em> black holes with initial masses up to <span class="math-container">$\sim 10^5$</span> times that of the Sun might have provided the seeds that enabled the rapid growth of supermassive black holes (e.g., <a href="https://arxiv.org/abs/1702.08275" rel="nofollow noreferrer">Garcia-Bellido 2017</a>; <a href="https://arxiv.org/abs/astro-ph/0204486" rel="nofollow noreferrer">Bean &amp; Magueijo 2020</a>; <a href="https://arxiv.org/abs/2002.12778" rel="nofollow noreferrer">Carr et al. 2021</a>).</p>

CC BY-SA 4.0
2023-06-22T15:19:53.957Z
2023-06-22T15:19:53.957Z
ProfRob
<p>I am a new user so if there is any error in this post kindly send it in the comment section so that I can improve my answer</p>
<p><strong>Maybe</strong>, but it all comes down to  the recessional velocity of the early expanding universe. If the reccesional velocity is high as in the Inflationary theory, The CMB might have not fed it enough energy to sustain, because the radical expansion would have acted too hastily and may have made the CMB's magnitude reduce too fast, and If the reccesional velocity is slow is true then the CMB might have gave it enough energy to form, till atoms began accumulate thus the odds of a blackhole actually existing till now is higher in theories with lower reccional velocity. All these primordial blackholes fall under the category of micro blackholes as they are very small to fit in other categories.</p>
<p>In fact, these blackholes may even be attached to now expanded topological defects in the spacetime continuum, known as <strong>cosmic string</strong> just  like wormholes (Riemann cuts in spacetime)</p>
<p>The probabilities of a primordial blackhole becoming a SMBH is greater if the mass of the primordial blackhole is larger as<br />
bigger primordial blackholes emit less Hawking radiation as compared to smaller ones.</p>
<p>Plus if we assume that in the early universe, had Quark-gluon plasma with no strong enough convective currents and eddies to make the dense pocket spin then according to the <strong>No-hair theorem</strong>,  we may be able to identify whether it is a primordial blackhole or not.</p>
<p>A piece of evidence that I would like to suggest against it would be that we have not seen any electromagnetic radiation or photons (whose frequency would be reduced by cosmological redshfit) from primordial blackholes.</p>
<p>Thanks!</p>

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2023-06-24T02:39:51.967Z
Kindle leave a vote or a comment for me to improve upon my answer. Thanks!
Arjun
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2023-06-26T10:13:36.583Z
Sure, here are my comments. Big Bang and inflation are not mutually exclusive. Big Bang is a broad and kind of vague term, but it typically refers to the idea that the Universe was hot and dense in the past. That would be the state after inflation.
Sten
CC BY-SA 4.0
2023-06-26T10:13:53.780Z
The rest of the first paragraph is kind of confusing to me, but the basic mechanism for PBH formation is that a region is too dense and/or expanding too slowly (due to coordinate freedom these are not really different things). Inflation or not doesn't really change that story. Inflation gives a concrete way to make sufficiently extreme density variations, but they could exist by other means too. (Note that cosmic strings are an alternative PBH formation mechanism, with different requirements.)
Sten
CC BY-SA 4.0
2023-06-26T10:14:06.250Z
"Probability proportional to mass" is kind of awkward, it's not proportional in a mathematical sense. Due to how strongly evaporation scales with mass, there is a rather sharp cutoff around $10^{17}$ gram ($10^{-16}$ solar mass) below which PBHs are not viable, at least assuming the semiclassical Hawking radiation calculation is accurate at such scales. See [Constraints on Primordial Black Holes](https://arxiv.org/abs/2002.12778).
Sten
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2023-06-29T09:13:51.240Z
Thanks a lot!. I will use this information to improve my answer.
Arjun
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2023-06-22T12:34:51.067Z
2023-07-02T08:26:49.300Z
2023-07-02T08:26:49.300Z
Arjun
<p>I don't think so. Primordial blackholes are formed by the gravitational collapse of inhomogeneous regions of density in early universe. These regions instead of expanding with the universe, decreased in size, as is validated by the fact that Black Holes evaporate with time until Page Time.</p>
<p>Even if primordial blackholes existed, only the contribution of significant changes in the mass density of the universe, or by contributions to gamma-ray background could be used to detect the same. Given, primordial blackholes were formed in the early Universe, all the primordial black holes are &quot;likely&quot; in the final stages of complete evaporation. Refer to Page et al. 1976.</p>
<p>Also, no gamma ray contribution of significance has been found in regards to primordial black holes based on Hawking &amp; Page, 1976.</p>
<p>Hence, referring to the original question, the odds of such an event occurring is extremely unlikely.</p>

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2023-06-16T19:15:54.073Z
Massive primordial black holes might exist and would not be evaporating.
ProfRob
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2023-06-16T21:08:05.940Z
Could you please elaborate on that ? I genuinely don't know. Also, if they won't be evaporating by now, then aren't they certainly before their Page Time, leading to the fact that they might not be primordial in the first place. Also, if they aren't evaporating, what about the particle creation at their horizon. Isn't the evaporation necessary to conserve the entropy due to the particle creation that happens at horizon. I think I am missing something.
AjayAg
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2023-06-16T21:59:30.300Z
They would be absorbing more mass from the CMB than they would lose from Hawking radiation.
ProfRob
CC BY-SA 4.0
2023-06-16T17:17:03.583Z
2023-06-16T17:17:03.583Z
AjayAg
<p>If primordial black hole do exists today could it be responsible for galaxies maybe even quasars, I mean these ancient monsters gobble up all materials in its wake and grow bigger and eventually evolves into say milky way galaxy etc. What are the odds of such events actually happened?</p>

CC BY-SA 3.0
2016-11-14T09:18:20.343Z
This is speculation. The seeds of supermassive black holes could be primordial black holes, which may exist, but they can also be black holes seeded by the collapse of massive stars, which we know happens.
ProfRob
CC BY-SA 3.0
2016-11-14T09:26:53.917Z
@Rob Jeffries: I think all black hole we see inherited properties like angular momentum and mass from its former self so could primordial black hole be any different so we can distinguish them?
user6760
CC BY-SA 3.0
2016-12-07T02:47:56.097Z
Its possible that there were primordial black holes of a few hundred solar masses or less.  These could then have accreted matter around them to grow into the supermassive black holes at the centers of galaxies.  But, it is speculative at this point and it would be hard to tell by looking at one today.  One would need to see them at very high redshift (lookback time).
eshaya
CC BY-SA 4.0
2023-06-22T15:44:00.813Z
N-body calculations with dark matter particles already form enough galaxies.  So, PBHs not needed.
eshaya
<galaxy><supermassive-black-hole>
Could a super massive black hole actually be primordial black hole in disguise?
user6760
# Could a super massive black hole actually be primordial black hole in disguise?

(Asked by: username_0 on 2016-11-14)

If primordial black hole do exists today could it be responsible for galaxies maybe even quasars, I mean these ancient monsters gobble up all materials in its wake and grow bigger and eventually evolves into say milky way galaxy etc. What are the odds of such events actually happened?

**Tags:** galaxy, supermassive-black-hole
> **Comments:**
> **username_1**: This is speculation. The seeds of supermassive black holes could be primordial black holes, which may exist, but they can also be black holes seeded by the collapse of massive stars, which we know happens.  
> **username_0**: @Rob Jeffries: I think all black hole we see inherited properties like angular momentum and mass from its former self so could primordial black hole be any different so we can distinguish them?  
> **username_2**: Its possible that there were primordial black holes of a few hundred solar masses or less.  These could then have accreted matter around them to grow into the supermassive black holes at the centers of galaxies.  But, it is speculative at this point and it would be hard to tell by looking at one today.  One would need to see them at very high redshift (lookback time).  
> **username_2**: N-body calculations with dark matter particles already form enough galaxies.  So, PBHs not needed.  

---

## 3 answers

### Answer by username_1 on 2023-06-22. Score: 3

Some people certainly think that primordial black holes could account for a significant fraction of dark matter and at least provide the seeds for growing supermassive black holes in the early universe.

One of the the most pressing puzzles in cosmology and the study of early galaxies is how you can find quasars which have inferred central black hole masses of a billion times that of the Sun (or more) in existence just a few hundred million years after the big bang. There are a number of suggested solutions, but one of these is indeed that *primordial* black holes with initial masses up to $\sim 10^5$ times that of the Sun might have provided the seeds that enabled the rapid growth of supermassive black holes (e.g., [Garcia-Bellido 2017](https://arxiv.org/abs/1702.08275); [Bean & Magueijo 2020](https://arxiv.org/abs/astro-ph/0204486); [Carr et al. 2021](https://arxiv.org/abs/2002.12778)).


---

### Answer by username_3 on 2023-06-22. Score: 1

I am a new user so if there is any error in this post kindly send it in the comment section so that I can improve my answer

**Maybe**, but it all comes down to the recessional velocity of the early expanding universe. If the reccesional velocity is high as in the Inflationary theory, The CMB might have not fed it enough energy to sustain, because the radical expansion would have acted too hastily and may have made the CMB's magnitude reduce too fast, and If the reccesional velocity is slow is true then the CMB might have gave it enough energy to form, till atoms began accumulate thus the odds of a blackhole actually existing till now is higher in theories with lower reccional velocity. All these primordial blackholes fall under the category of micro blackholes as they are very small to fit in other categories.

In fact, these blackholes may even be attached to now expanded topological defects in the spacetime continuum, known as **cosmic string** just like wormholes (Riemann cuts in spacetime)

The probabilities of a primordial blackhole becoming a SMBH is greater if the mass of the primordial blackhole is larger as  
bigger primordial blackholes emit less Hawking radiation as compared to smaller ones.

Plus if we assume that in the early universe, had Quark-gluon plasma with no strong enough convective currents and eddies to make the dense pocket spin then according to the **No-hair theorem**, we may be able to identify whether it is a primordial blackhole or not.

A piece of evidence that I would like to suggest against it would be that we have not seen any electromagnetic radiation or photons (whose frequency would be reduced by cosmological redshfit) from primordial blackholes.

Thanks!

> **Comments:**
> **username_3**: Kindle leave a vote or a comment for me to improve upon my answer. Thanks!  
> **username_4**: Sure, here are my comments. Big Bang and inflation are not mutually exclusive. Big Bang is a broad and kind of vague term, but it typically refers to the idea that the Universe was hot and dense in the past. That would be the state after inflation.  
> **username_4**: The rest of the first paragraph is kind of confusing to me, but the basic mechanism for PBH formation is that a region is too dense and/or expanding too slowly (due to coordinate freedom these are not really different things). Inflation or not doesn't really change that story. Inflation gives a concrete way to make sufficiently extreme density variations, but they could exist by other means too. (Note that cosmic strings are an alternative PBH formation mechanism, with different requirements.)  
> **username_4**: "Probability proportional to mass" is kind of awkward, it's not proportional in a mathematical sense. Due to how strongly evaporation scales with mass, there is a rather sharp cutoff around $10^{17}$ gram ($10^{-16}$ solar mass) below which PBHs are not viable, at least assuming the semiclassical Hawking radiation calculation is accurate at such scales. See [Constraints on Primordial Black Holes](https://arxiv.org/abs/2002.12778).  
> **username_3**: Thanks a lot!. I will use this information to improve my answer.  

---

### Answer by username_5 on 2023-06-16. Score: 0

I don't think so. Primordial blackholes are formed by the gravitational collapse of inhomogeneous regions of density in early universe. These regions instead of expanding with the universe, decreased in size, as is validated by the fact that Black Holes evaporate with time until Page Time.

Even if primordial blackholes existed, only the contribution of significant changes in the mass density of the universe, or by contributions to gamma-ray background could be used to detect the same. Given, primordial blackholes were formed in the early Universe, all the primordial black holes are "likely" in the final stages of complete evaporation. Refer to Page et al. 1976.

Also, no gamma ray contribution of significance has been found in regards to primordial black holes based on Hawking & Page, 1976.

Hence, referring to the original question, the odds of such an event occurring is extremely unlikely.

> **Comments:**
> **username_1**: Massive primordial black holes might exist and would not be evaporating.  
> **username_5**: Could you please elaborate on that ? I genuinely don't know. Also, if they won't be evaporating by now, then aren't they certainly before their Page Time, leading to the fact that they might not be primordial in the first place. Also, if they aren't evaporating, what about the particle creation at their horizon. Isn't the evaporation necessary to conserve the entropy due to the particle creation that happens at horizon. I think I am missing something.  
> **username_1**: They would be absorbing more mass from the CMB than they would lose from Hawking radiation.  

---

