Dark Matter:

[beecee]

 DM is as yet an unknown form of matter that is needed to explain anomalous  rotational curves of galaxies, as well as structual galactic formation in general. Without it, means that our whole picture and theories about gravity is wrong. That is viewed as unlikely as it works so well in all other aspects...hence the unknown missing non baryonic mass hypothesis.

In actual fact the name DM is more an expression of cosmological ignorance then anything else, much as the old ancient cartographers often marked unknown regions of the world at that time, as "terra incognita" 

The best observational evidence we have for non baryonic DM, is the bullet cluster anomaly.

Some of the missing mass is baryonic and simply stellar remnants and failed stars, that emit little or no radiation.

Recently I reproduced an article here...https://phys.org/news/2021-12-black-holes-immediately-big.html with regards to micro BH's or primordial BH's.

This has me wondering if it maybe the answer to the missing mass problem. So what I need is for someone to convince me that this cannot be the case, or at best simply highly unlikely. The very early universe, post BB (the first three minutes) was a chaotic violent place, and there existed only our most fundamental basic sub atomic particles.

Is there any reason (not stated in the article) why micro and primordial BH's may not be the missing mass?

[swansont]

It’s being studied/considered

https://news.miami.edu/stories/2021/12/are-black-holes-and-dark-matter-the-same.html

https://www.quantamagazine.org/black-holes-from-the-big-bang-could-be-the-dark-matter-20200923/

[MigL]

The problem is that Black Holes have entropy, and therefore a characteristic temperature and associated black body radiation, also known as Hawking radiation.
Most Black Holes are greater than stellar size, and very cool. much less than the CMB radiation, but as they get smaller ( or start out much smaller, even microscopic ), their temperature increases dramatically, and the radiation emitted is more energetic.
Eventually, when small enough, they don't have the mass to support an event horizon, and essentially de-collapse in a large explosion of highly energetic radiation.
This Gamma ray burst would be the tell-tale of a microscopic Black Hole's final evaporation.

If we know the size of a Black Hole, even primordial ones, we can compare to the CMB as it cooled, and we can estimate how long it would take for microscopic Black Holes to evaporate, and it turns out that primordial microscopic Black Holes would have evaporated by now.
IOW, as we look out into the universe, and back in time, we should be seeing the tell-tale Gamma ray bursts that are the last gasps of these primordia; black holes that formed in the high energy densities shortly after the Big Bang.
None have ever been recorded.

[beecee]

5 hours ago, swansont said:

It’s being studied/considered

https://news.miami.edu/stories/2021/12/are-black-holes-and-dark-matter-the-same.html

https://www.quantamagazine.org/black-holes-from-the-big-bang-could-be-the-dark-matter-20200923/

Thanks for that.

4 hours ago, MigL said:

IOW, as we look out into the universe, and back in time, we should be seeing the tell-tale Gamma ray bursts that are the last gasps of these primordia; black holes that formed in the high energy densities shortly after the Big Bang.
None have ever been recorded.

While you have made some good points, we are seeing GRB's every day, and FRB's also.......https://www.space.com/gamma-ray-burst.html

"Gamma-ray bursts also seem to focus their energy in a narrow beam, rather than emitting it equally in every direction, meaning that our satellites are missing many of them. Astronomers estimate that, although satellites spot about one gamma-ray burst per day, roughly 500 are occurring within the same time period. 

So far, gamma-ray bursts have only been detected in distant galaxies".

https://www.google.com/search?q=how+many+Gamma+ray+bursts+have+we+seen&rlz=1C1RXQR_en-GBAU952AU952&oq=how+many+Gamma+ray+bursts+have+we+seen&aqs=chrome..69i57j33i160.13448j0j7&sourceid=chrome&ie=UTF-8

How many gamma ray bursts are there?

 

"Astronomers estimate that, although satellites spot about one gamma-ray burst per day, roughly 500 are occurring within the same time period. So far, gamma-ray bursts have only been detected in distant galaxies. However, it is possible for one to occur in our Milky Way galaxy".

[MigL]

All observed Gamma ray bursts are directional in nature.
That is because they are caused by the influx of rotating ionized material as supernovae clollapse into Black Holes or neutron stars.
The polar jets are produced perpendicular to the plane of accretion.
Other classes of Gamma ray bursts are produced from mergers of neutron stars, and are similarly directional, because of orbital motion.

The Gamma ray burst from the end-of-life explosion/evaporation of a microscopic Black Hole would not be directional, as there is no rotating infalling ionized material to produce polar radiation.
It would most likely be an omni-directional burst, and as far as I know, none of the sort have been observed.

[joigus]

On 12/20/2021 at 3:10 AM, MigL said:

All observed Gamma ray bursts are directional in nature.

How do we know this?

[MigL]

2 hours ago, joigus said:

How do we know this?

"Gamma-ray bursts are thought to be highly focused explosions, with most of the explosion energy collimated into a narrow jet.^[78][79] The approximate angular width of the jet (that is, the degree of spread of the beam) can be estimated directly by observing the achromatic "jet breaks" in afterglow light curves: a time after which the slowly decaying afterglow begins to fade rapidly as the jet slows and can no longer beam its radiation as effectively.^[80][81] Observations suggest significant variation in the jet angle from between 2 and 20 degrees.^[82]

Because their energy is strongly focused, the gamma rays emitted by most bursts are expected to miss the Earth and never be detected. When a gamma-ray burst is pointed towards Earth, the focusing of its energy along a relatively narrow beam causes the burst to appear much brighter than it would have been were its energy emitted spherically. When this effect is taken into account, typical gamma-ray bursts are observed to have a true energy release of about 10⁴⁴ J, or about 1/2000 of a Solar mass (M_☉) energy equivalent^[82] – which is still many times the mass-energy equivalent of the Earth (about 5.5 × 10⁴¹ J). This is comparable to the energy released in a bright type Ib/c supernova and within the range of theoretical models. Very bright supernovae have been observed to accompany several of the nearest GRBs.^[36] Additional support for focusing of the output of GRBs has come from observations of strong asymmetries in the spectra of nearby type Ic supernova^[83] and from radio observations taken long after bursts when their jets are no longer relativistic.^[84]

Short (time duration) GRBs appear to come from a lower-redshift (i.e. less distant) population and are less luminous than long GRBs.^[85] The degree of beaming in short bursts has not been accurately measured, but as a population they are likely less collimated than long GRBs^[86] or possibly not collimated at all in some cases.^[87]"

^From

Gamma-ray burst - Wikipedia