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

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,