Primordial black hole
In 1966, Yakov Zeldovich and Igor Novikov first proposed the existence of such black holes,[1] while the first in-depth study was conducted by Stephen Hawking in 1971.
In September 2022, primordial black holes were proposed by some researchers to explain the unexpected very large early galaxies discovered by the James Webb Space Telescope (JWST).
[3][4] PBHs have long been considered possibly important if not nearly exclusive components of dark matter,[5][6][7][8] the latter perspective having been strengthened by both LIGO/Virgo interferometer gravitational wave and JWST observations.
However, primordial black holes originally having masses lower than 1011 kg would not have survived to the present due to Hawking radiation, which causes complete evaporation in a time much shorter than the age of the Universe.
They are naturally a good dark matter candidate: they are (nearly) collision-less and stable (if sufficiently massive), they have non-relativistic velocities, and they form very early in the history of the Universe (typically less than one second after the Big Bang).
[21] Nevertheless, critics maintain that tight limits on their abundance have been set up from various astrophysical and cosmological observations, which would exclude that they contribute significantly to dark matter over most of the plausible mass range.
The third group claimed that these merging rates are incompatible with an all-dark-matter scenario and that primordial black holes could only contribute to less than one percent of the total dark matter.
In May 2016, Alexander Kashlinsky suggested that the observed spatial correlations in the unresolved gamma-ray and X-ray background radiations could be due to primordial black holes with similar masses, if their abundance is comparable to that of dark matter.
[29] In August 2019, a study was published opening up the possibility of making up all dark matter with asteroid-mass primordial black holes (3.5 × 10−17 – 4 × 10−12 solar masses, or 7 × 1013 – 8 × 1018 kg).
[34] In September 2022, primordial black holes were used to explain the unexpected very large early (high redshift) galaxies discovered by the James Webb Space Telescope.
This discovery was found in studies of UHZ1, a very early galaxy containing a quasar, by the Chandra X-ray Observatory and James Webb Space Telescope.
While evidence that primordial black holes may constitute dark matter is inconclusive as of 2023, researchers such as Bernard Carr and others are strong proponents.
[49] In essence, the energy stored in the fourth spatial dimension as a stationary wave would bestow a significant rest mass to the object when regarded in the conventional four-dimensional space-time.
If they observe specific small interference patterns within gamma-ray bursts, it could be the first indirect evidence for primordial black holes and string theory.
Stephen Hawking theorized in 1974 that large numbers of such smaller primordial black holes might exist in the Milky Way in our galaxy's halo region.
If such low-mass black holes were created in sufficient number in the Big Bang, we should be able to observe explosions by some of those that are relatively nearby in our own Milky Way galaxy.
NASA's Fermi Gamma-ray Space Telescope satellite, launched in June 2008, was designed in part to search for such evaporating primordial black holes.
Fermi data set up the limit that less than one percent of dark matter could be made of primordial black holes with masses up to 1013 kg.
Evaporating primordial black holes would have also had an impact on the Big Bang nucleosynthesis and change the abundances of light elements in the Universe.
However, if theoretical Hawking radiation does not actually exist, such primordial black holes would be extremely difficult, if not impossible, to detect in space due to their small size and lack of large gravitational influence.
