A team of astronomers have conducted a search for distant super massive
black holes and they have found 83 of them. See:

https://www.princeton.edu/news/2019/...early-universe

Here is the report about one of those:
https://iopscience.iop.org/article/1...13/ab0216/meta
"Discovery of the First Low-luminosity Quasar at z 7"
[[Mod. note -- preprint is Matsuoka et al, arXiv:1901.10487 -- jt]]

What is interesting is that contrary to the expectations of the big bang
hypothesis, the density of those beasts is not at all higher than now.

According to BB theory, the neutral hydrogen was reionized after the
"dark ages". Where would the huge amount of energy necessary for
reionization come from?

The standard answer was that massive black holes would provide it... but
apparently the density of black holes 13 Gy ago was no higher than now.

I quote:
"...but astronomers still don't know what provided the incredible amount
of energy required to cause the reionization. A compelling hypothesis
suggests that there were many more quasars in the early universe than
detected previously, and it is their integrated radiation that reionized
the universe.
However, the number of quasars we observed shows that this is not the
case," explained Robert Lupton, a 1985 Princeton Ph.D. alumnus who is a
senior research scientist in astrophysical sciences. "The number of
quasars seen is significantly less than needed to explain the
reionization."

The team supposes that they will detect super massive black holes even
farther away... what would make the question of how a super massive
black hole could appear in such a small amount of time: just 760 million
years...

Another quasar that is remarkable is J043947.08+163415.7 that shines
brightly with the light of 600 trillion suns. But that object is lensed,
so we have to divide by a factor of 50 to get the real luminosity. After
taking the gravitational lensing into accopunt it becomes just a normal
800 million sun masses object.

It is just 1GY away from the supposed bang.
(https://www.spacetelescope.org/news/heic1902/#1)

We are at the limit of current scopes. I am confident that in a few
years we will find even farther away quasars.

[[Mod. note --
A few comments:
1. It's important to distinguish between quasars and supermassive black
holes. We think that quasars are supermassive BHs which are accreting
matter... but there may (probably are) also other supermassive BHs
which aren't accreting much matter, and hence are "dark", not giving
off much light or other electromagnetic radiation. There are a lot
harder to detect.
2. Did Matsuoka et al discuss the space density of such quasars? I don't
see anything about that in a quick skim of their preprint.
3. I've never seen it suggested that quasars were the *only* source of
energetic photons for reionization. Population III stars and dwarf
galaxies were probably also important; I don't know if we know much
about their relative contributions (as a function of redshift).
4. The author is surely right that in the coming years will find even
fainter & higher-redshift/more-distant quasars. Looking at the
planned sensitivity of the coming generation of 20-40-meter telescopes
is enough to make an optical astronomer salivate!
-- jt]]