American Physics Society | Physics Viewpoint | 2018 Jul 03
Recent observations of hydrogen absorption that occurred when the first stars turned on may give insights into the nature of dark matter, new analyses show.
The nature of the dark matter is one of the longest-standing puzzles in cosmology. Astronomers have established that dark matter is the dominant constituent of matter in the Universe, but they are still in the dark about its identity. A possible clue may have been uncovered by recent observations of the cosmic dawn—the epoch when the first stars formed. Earlier this year, researchers reported a surprisingly strong absorption signal coming from gas activated by light from the first stars [1]. Now, a series of new papers [2–5] has explored what might be inferred about dark matter from this unexpected absorption. For example, the absorption could be explained by assuming that dark matter carries a small electric charge that allows it to interact weakly with ordinary matter. On the flip side, the absorption is inconsistent with certain models that predict dark matter should annihilate with itself. Regardless of the final interpretation, the cosmic dawn has clearly opened a new path toward resolving the dark matter puzzle.Artist’s concept of the first stars - Credit: Adolf Schaller (STScI)
For nearly a century [6], scientists have been studying dark matter through its gravitational effects on visible matter and radiation. Those observations have confirmed that dark matter is one of the primary constituents of the Universe. The measured anisotropies of the cosmic microwave background (CMB), for example, have shown that the overall density of dark matter is about five times that of ordinary (baryonic) matter. But the anisotropies are not the only aspect of the CMB that may contain information about the matter in the Universe. The CMB light carries an imprint of hydrogen gas that it encountered along its journey—a journey that started 400,000 years after the big bang. The imprinted signal is due to absorption of CMB photons with 21-cm wavelength, corresponding to the electronic transition in hydrogen’s hyperfine levels (see Fig. 2). Because the universe is expanding, this absorption is redshifted to longer wavelengths, so that observations at a particular wavelength correspond to a specific time in the past. ...
Constraining Baryon–Dark-Matter Scattering with the Cosmic Dawn 21-cm Signal - Anastasia Fialkov et al
- Physical Review Letters 121(01):1101 (06 Jul 2018) DOI: 10.1103/PhysRevLett.121.011101
arXiv.org > astro-ph > arXiv:1802.10577 > 28 Feb 2018
- Physical Review Letters 121(01):1102 (06 Jul 2018) DOI: 10.1103/PhysRevLett.121.011102
arXiv.org > astro-ph > arXiv:1803.02804 > 07 Mar 2018
- Physical Review Letters 121(01):1103 (06 Jul 2018) DOI: 10.1103/PhysRevLett.121.011103
arXiv.org > astro-ph > arXiv:1803.03629 > 09 Mar 2018 (v1), 24 Apr 2018 (v2)