Astronomy & Telescopes

The Impact Of The Cosmological Constant On Past And Future Star Formation

By Keith Cowing
Status Report
astro-ph.CO)
November 23, 2024
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The Impact Of The Cosmological Constant On Past And Future Star Formation
Upper panels: Cosmic star formation rate density, as computed with our extension of the SP21 model (dashed black line) and as given by the original SP21 model (dot-dashed red line). In the left panel, we further show with the empirical fit (dotted black line) to a compilation of observational data provided by Madau & Dickinson (2014) (grey data points). The right panel shows the behaviour of the SP21 model and our extended formalism in the future of the universe. As future times correspond to negative redshifts, and the cosmic star formation rate density becomes asymptotically null at arbitrarily large times, both axes switch from logarithmic to linear scale when moving from the left to the right panel. The grey hatched shaded area in the right panel excludes the non-physical region corresponding to 𝜌¤∗ < 0. Lower panels: Relative difference between the two models showed above (dashed black line), and between our formalism and the fit from Madau & Dickinson (2014) (dotted black line). The latter comparison is available only for positive redshifts (i.e., past cosmic times), as the fit represents a purely empirical fit to the data, and not a predictive theoretical model. The SP21 model agrees well with the improved method introduced in this work at high redshift, but overestimates the cosmic star formation rate density at lower redshift and in the future. In the redshift range 0 < 𝑧 < 10, both the original SP21 model and our updated formalism agree with the empirical fit within a factor of ∼ 2. -- astro-ph.CO

We present an extended analytic model for cosmic star formation, with the aim of investigating the impact of cosmological parameters on the star formation history within the ΛCDM paradigm.

Constructing an ensemble of flat ΛCDM models where the cosmological constant varies between Λ=0 and 105 times the observed value, Λobs, we find that the fraction of cosmic baryons that are converted into stars over the entire history of the universe peaks at ∼27% for 0.01≲Λ/Λobs≲1.

We explain, from first principles, that the decline of this asymptotic star-formation efficiency for lower and higher values of Λ is driven respectively by the astrophysics of star formation, and by the suppression of cosmic structure formation.

However, the asymptotic efficiency declines slowly as Λ increases, falling below 5% only for Λ>100Λobs. Making the minimal assumption that the probability of generating observers is proportional to this efficiency, and following Weinberg in adopting a flat prior on Λ, the median posterior value of Λ is 539Λobs.

Furthermore, the probability of observing Λ≤Λobs is only 0.5%. Although this work has not considered recollapsing models with Λ<0, the indication is thus that Λobs appears to be unreasonably small compared to the predictions of the simplest multiverse ensemble.

This poses a challenge for anthropic reasoning as a viable explanation for cosmic coincidences and the apparent fine-tuning of the universe: either the approach is invalid, or more parameters than Λ alone must vary within the ensemble.

Daniele Sorini, John A. Peacock, Lucas Lombriser

Comments: Published in the Monthly Notices of the Royal Astronomical Society (MNRAS). This is a pre-copyedited, author-produced version of the article accepted for publication in MNRAS following peer review. The version of record is available online at the DOI: https://doi.org/10.1093/mnras/stae2236
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2411.07301 [astro-ph.CO](or arXiv:2411.07301v1 [astro-ph.CO] for this version)
https://doi.org/10.48550/arXiv.2411.07301
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Related DOI:
https://doi.org/10.1093/mnras/stae2236
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Submission history
From: Daniele Sorini
[v1] Mon, 11 Nov 2024 19:00:28 UTC (2,968 KB)
https://arxiv.org/abs/2411.07301

Astrobiology, Cosmology, Stellar Cartography,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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