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| recombination (cosmology) | |
|---|---|
| Name | Recombination (cosmology) |
| Epoch | Big Bang |
| Era | Radiation-dominated era, Matter-dominated era |
| Start | ~380,000 years after Big Bang |
| Key people | George Gamow, Ralph Alpher, Robert Herman, W. A. Fowler, Zel'dovich, Yakov Borisovich Zel'dovich |
| Important observations | Cosmic Microwave Background, COBE, WMAP, Planck (spacecraft) |
| Related concepts | Photon decoupling, Last Scattering Surface, Baryon acoustic oscillations, Primordial nucleosynthesis |
recombination (cosmology) Recombination in cosmology denotes the epoch when free electrons and protons combined to form neutral atoms, allowing photons to decouple and propagate, producing the Cosmic Microwave Background. Occurring roughly 370,000–400,000 years after the Big Bang, this transition marks the end of the tightly coupled photon–baryon fluid and the effective beginning of large-scale structure growth under gravitation. Studies of recombination link theoretical work by George Gamow, observational results from COBE, WMAP, and Planck (spacecraft), and computational advances in radiative transfer and atomic physics.
Recombination follows Primordial nucleosynthesis and precedes the epoch of Reionization, defining the observable Last Scattering Surface probed by missions like COBE, WMAP, and Planck (spacecraft). The process depends on cosmological parameters constrained by projects such as Sloan Digital Sky Survey, Baryon Oscillation Spectroscopic Survey, and collaborations like European Space Agency and NASA. Historical context ties to theoretical predictions by George Gamow, Ralph Alpher, and Robert Herman and precision fits to data from John Mather-led and Charles L. Bennett-led teams. Recombination physics interplays with phenomena studied by groups at institutions including Harvard University, Princeton University, California Institute of Technology, and Max Planck Institute for Astrophysics.
Atomic processes during recombination involve hydrogen and helium level populations, radiative cascades, and two-photon decays, analyzed with quantum mechanics developed by pioneers like Niels Bohr and Erwin Schrödinger in frameworks used at Cavendish Laboratory-linked research. The Saha equation initially approximates ionization balance, but departures require time-dependent solutions implemented in codes influenced by methods from Richard Feynman and computational paradigms used at Los Alamos National Laboratory. Relevant atomic rates draw on measurements and theory from laboratories such as National Institute of Standards and Technology and collaborations with observatories like Keck Observatory and Very Large Telescope. Interactions of photons, electrons, and baryons mediated by Thomson scattering are critical, connecting to analyses by Lev Landau and scattering formalisms in plasma physics advanced at Princeton Plasma Physics Laboratory.
The thermal history transitions from the Radiation-dominated era to the Matter-dominated era, with recombination occurring when the photon temperature fell to ~3000 K. Timeline fitting uses cosmological parameter estimation techniques from Alan Guth-inspired inflationary models and constraints from Andrei Linde-type inflationary scenarios. Prior epochs include baryogenesis and Primordial nucleosynthesis driven by processes explored by Hans Bethe and Alpher–Bethe–Gamow-era theory. After recombination, residual ionization and cooling set the stage for structure formation studied by research groups at Institute for Advanced Study and Space Telescope Science Institute.
Photon decoupling at recombination produces the primary anisotropies and acoustic peaks observed by COBE, WMAP, and Planck (spacecraft) and analyzed in studies led by figures like John C. Mather, Charles L. Bennett, and Rafael Rebolo. The angular power spectrum encodes baryon density, dark matter content, and curvature parameters constrained jointly by datasets from Atacama Cosmology Telescope, South Pole Telescope, and surveys like 2dF Galaxy Redshift Survey. Polarization signatures (E-modes, B-modes) connect recombination-era physics to projects such as BICEP2 and missions by European Space Agency and NASA.
A small residual free-electron fraction persists after recombination, influencing the optical depth to Thomson scattering measured by Planck (spacecraft) and informing the timing of reionization driven by first stars and quasars observed in surveys like Hubble Ultra Deep Field, and studied in programs at Space Telescope Science Institute. Residual ionization affects molecule formation pathways (e.g., H2) relevant to Population III star formation models developed by groups at University of California, Santa Cruz and Yale University. The eventual Epoch of Reionization involves sources cataloged by Sloan Digital Sky Survey and theoretical work from Harvard-Smithsonian Center for Astrophysics.
High-precision modeling employs codes such as RECFAST, HyRec, and CosmoRec, developed by teams affiliated with Cambridge University, Oxford University, and Max Planck Institute for Astrophysics. Boltzmann solvers like CAMB and CLASS, created by collaborations including researchers at Institute for Advanced Study and Institut d'Astrophysique de Paris, couple recombination histories to anisotropy predictions. Parameter inference uses Bayesian frameworks implemented in CosmoMC and Monte Carlo techniques popularized in projects at CERN and Fermilab.
Observations constraining recombination include the CMB anisotropy spectrum from Planck (spacecraft), lensing maps from Atacama Cosmology Telescope, and small-scale studies by South Pole Telescope. Measurements inform cosmological parameters used in concordance models advanced by collaborations such as Supernova Cosmology Project and High-Z Supernova Search Team. Secondary signatures—spectral distortions, recombination lines, and anisotropy damping—are targets for future missions like proposed next-generation probes from European Space Agency and initiatives within NASA programs.