The second flavor of hydrogen atoms constitutes most of baryonic dark matter.

The Second Flavor of Hydrogen Atoms (SFHAs) are hydrogen atoms that have only the S-states, these states being described by the second solution of the standard Dirac equation outside the proton. Their existence is evidenced by four different types of atomic/molecular experiments. The SFHA-based explanations of two perplexing astrophysical puzzles, i.e. of the abnormal absorption in the 21 cm spectral line from the early universe and of the less nubby dark matter distribution in the universe than predicted by the standard cosmology, made the SFHA a compelling candidate for the baryonic dark matter. In distinction to the overwhelming majority of dark matter hypotheses resorting to never discovered subatomic particles or to modifications of the existing physical laws, the SFHA, being based on the standard Dirac equation of quantum mechanics, does not go beyond the Standard Model of particle physics and does not require modifying the existing physical laws, which is why it is favored by the Occam razor principle. In the present paper, first, we show that the SFHA, as the candidate for the baryonic dark matter, does not contradict the known cosmological constraints. Second, based on the cosmological data we demonstrate that the SFHA seems to constitute most of the baryonic dark matter. We also refer to the latest results showing that neutron stars can slowly but continuously generate the baryonic dark matter in the form of the SFHA. Finally, we discuss/motivate some relevant future laboratory experiments and astrophysical observations. [ABSTRACT FROM AUTHOR]