An absorption profile centred at 78 megahertz in the sky-averaged spectrum

By Judd D. Bowman, A. Rogers, R. Monsalve, T. Mozdzen, N. Mahesh. Nature, 2018

984 citations recorded by the source corpus.

After stars formed in the early Universe, their ultraviolet light is expected, eventually, to have penetrated the primordial hydrogen gas and altered the excitation state of its 21-centimetre hyperfine line. This alteration would cause the gas to absorb photons from the cosmic microwave background, producing a spectral distortion that should be observable today at radio frequencies of less than 200 megahertz. Here we report the detection of a flattened absorption profile in the sky-averaged radio spectrum, which is centred at a frequency of 78 megahertz and has a best-fitting full-width at half-maximum of 19 megahertz and an amplitude of 0.5 kelvin. The profile is largely consistent with expectations for the 21-centimetre signal induced by early stars; however, the best-fitting amplitude of the profile is more than a factor of two greater than the largest predictions. This discrepancy suggests that either the primordial gas was much colder than expected or the background radiation temperature was hotter than expected. Astrophysical phenomena (such as radiation from stars and stellar remnants) are unlikely to account for this discrepancy; of the proposed extensions to the standard model of cosmology and particle physics, only cooling of the gas as a result of interactions between dark matter and baryons seems to explain the observed amplitude. The low-frequency edge of the observed profile indicates that stars existed and had produced a background of Lyman-α photons by 180 million years after the Big Bang. The high-frequency edge indicates that the gas was heated to above the radiation temperature less than 100 million years later.

Subfields: Aerospace Engineering, Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/fb5ec5f8ffccd3f77ef4a91278d8aed60668ecff

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Citations in the corpus

Fundamental physics with the Square Kilometre Array (2018, background): “Recently, EDGES reported a detection of the global 21 cm signal in absorption at a frequency of 78 MHz, corresponding to the redshift z ∼ 17 (Bowman et al., 2018).”
Unveiling the gravitational universe at μ-Hz frequencies (2019, background): “[51]) suggest that the first stars and black holes started forming 100–200 Myr after the Big Bang.”
Hubble Tension: The Evidence of New Physics (2023, background): “5-3σ), parity violating rotation of CMB linear polarization [67–70], small-scale curiosities [71–74], age of the universe [75], the Lithium problem [76] (2-4σ),the quasar Hubble diagram [77–81] (∼4σ), oscillating signals in short range gravity experiments [82,83], anomalously low baryon temperature ”
A Long Time Ago in a Galaxy Far, Far Away: A Candidate z ∼ 12 Galaxy in Early JWST CEERS Imaging (2022, methodology): “Additionally, the presence of this galaxy ∼370 Myr after the Big Bang may be consistent with redshifted 21 cm absorption at z∼ 18 reported by the Experiment to Detect the Global Epoch of Reionization Signature (EDGES; Bowman et al. 2018) presumed to be caused by light from the first stars.”
Clusters of Primordial Black Holes (2018, background): “Also one should take into account the data on baryon temperature at z ∼ 17, deduced from 21 cm absorption line of hydrogen observation [159], which may give extra restriction for PBH in a given mass range [160].”
Early Dark Energy can Resolve the Hubble Tension. (2018, result): “[50] J. Colin Hill and Eric J. Baxter, “Can Early Dark En- ergy Explain EDGES?””