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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Decay of long-lived particles in the early universe

It is pointed out that radiative decay of massive fermions can distort the cosmic background radiation. The present investigation is concerned with a study of decay lifetimes in the range from 10 to 100,000 years. Attention is given to the physics involved in determining the effect of radiative decay of massive fermions on observed photon backgrounds. The case of particles which decoupled when the effective number of species in equilibrium was in the range from 50 to 100 is considered, and constraints on particle masses and lifetimes are placed on the basis of observed photon fluxes. This approach provides results with special applications to particles predicted by supersymmetry theories and to right-handed neutrinos. Implications for galaxy formation are also discussed.

Silk, J.↗
NASA NTRS1984

Matter antimatter domains: A possible solution to the CP domain wall problem in the early universe

An SU(5) grand unified theory model is used to show how the degeneracy between vacua with different spontaneously broken charge parity can be dynamically lifted by a condensate of heavy fermion pairs. This drives a phase transition to a unique vacuum state with definite charge parity. The transition eliminates the domain walls in a matter antimatter symmetric domain cosmology.

Mohanty, A. K.↗
NASA NTRS1988

Needling the early universe

The possibility that the whole microwave background can be produced by a bright population of pregalactic stars at a redshift of a few hundred is explored. The radiation is thermalized by a combination of amorphous silicate, amorphous carbon, graphite, and needle-shaped conducting grains which give rise to the opacity needed at wavelengths greater than 3 cm. The occurrence of distortion in a primordial microwave background spectrum due to its interaction with Population III stars and dust is investigated. The possibility of producing deviations small enough to be consistent with the best available observations, but still detectable by COBE, is considered.

Hawkins, Isabel↗
NASA NTRS1990

Radiative shocks and nonequilibrium chemistry in the early universe - Galaxy and primordial star formation

The nonequilibrium radiative cooling, recombination, and molecule formation behind steady-state shock waves in primordial composition gas is studied. The hydrodynamical conservation equations are solved as well as equations for nonequilibrium ionization, recombination, and molecule formation and the equation of radiative transfer. The shocked gas is found to cool faster than it can recombine; as a result it is able to form an H2 concentration as high as 0.001 or higher via the formation of H(-) and H2(+) intermediaries due to the enhanced nonequilibrium ionization at 10,000 K. With such an H2 concentration, the gas cools by rotational-vibrational line excitation of H2 molecules to well below the canonical final temperature of 10,000 K for a molecule-free gas without metals. It is shown that, as the level of external ionizing and dissociating radiation flux is increased, the formation of and cooling by H2 molecules can be inhibited and delayed.

Shapiro, Paul R.↗
NASA NTRS1992

Let's go: Early universe 2. Primordial nucleosynthesis the computer way

This is a revised description and manual for the primordial nucleosynthesis program, NUC123, an updated and modified version of the code of R.V. Wagoner. NUC123 has undergone a number of changes, further enhancing its documentation and ease of use. Presented here is a guide to its use, followed by a series of appendices containing specific details such as a summary of the basic structure of the program, a description of the computational algorithm, and a presentation of the theory incorporated into the program.

Kawano, Lawrence↗
NASA NTRS1993

Neutrino Heat Conduction and Inhomogeneities in the Early Universe

Constraints on parameters of inhomogeneous nucteosynthesis, namely, the overdensity and size of baryon lumps, are found by calculatig the blackbody neutrino heat conduction into the lumps, which tends to inflate them away. The scale size for efficient heat conduction is determined by the mean free path lambda of the neutrino, and so we compute lambda in our case of a high-temperature plasma with low chemical potential, and find a general result that many-body effects are unimportant, simplifying the calculation. We find that in the region of interest for nucleosynthesis, neutrino inflation is important for overdensities greater than 10(exp 4).

Heckler, A.↗
NASA NTRS2003

Dominant Gamma-Ray Bursts Production in the Early Universe

It has been known that at least some of the observed gamma-ray bursts (GRBs) are produced at cosmological distances and the GRB production rate may follow the star formation rate. Here we report that the lower and upper distance limits to the GRB production are z approx. 0.22 and 8, respectively, as determined from BATSE's GRB fluence distribution. This result suggests that GRBs are no longer produced presently, and that the actual star formation rate peaks at much higher redshift and thus the 'dark ages' of the universe have ended much earlier than believed previously. We have also determined that the GRB opening angles follow an exponential distribution with a mean opening angle of about 0.03 radian. This study is supported in part by the Special Funds for Major State Basic Research Projects and by the National Natural Science Foundation of China. SNZ also acknowledges supports by NASA's Marshall Space Flight Center and through NASA's Long Term Space Astrophysics Program.

Zhang, S. N.↗
NASA NTRS2002

Dominant Gamma-Ray Bursts Production in the Early Universe

It has been known that at least some of the observed gamma-ray bursts (GRBs) are produced at cosmological distances and the GRB production rate may follow the star formation rate. Here we report that the lower and upper distance limits to the GRB production are z approx. 0.24 and z approx. 10, respectively. This result suggests that GRBs are no longer produced presently, and that the actual star formation rate peaks at much higher redshift and thus the 'dark ages' of the universe have ended much earlier than believed previously. This study is supported in part by the Special Funds for Major State Basic Research Projects and by the National Natural Science Foundation of China. SNZ also acknowledges supports by NASA's Marshall Space Flight Center and through NASA's Long Term Space Astrophysics Program.

Zhang, S. N.↗
NASA NTRS1997

SIRTF and the Early Universe

Explore the source record for details and available documents.

SIRTF rest frame two micron emission redshift of t↗
NASA NTRS1998

Near Infrared Observations of a Redshift 5.34 Galaxy: Further Evidence for Significant Dust Absorption in the Early Universe

In the last several years, the combination of new wavelength dropout discovery techniques coupled with the incredible power of deep imaging of the Hubble Space Telescope and the spectroscopic capabilities of a new generation of large ground-based telescopes, has lead to an astonishing blossoming of the study of galaxies at redshifts of z=2-4, when the Universe was less than 10-20% of its current age.

near infrared redshift 5.34 galaxy high redshift y↗
NASA NTRS2006

Astrochemistry in the Early Universe: Collisional Rates for H on H2

We present preliminary results of a full quantum calculation of state to state cross sections for H on H2. These cross sections are calculated for v=0,4 j=0,15 for energies up to 3.0 eV. The cross sections are calculated on the BKMP2 potential surface (Boothroyd et al. 1996) with the ABC scattering code (Skouteris et al. 2000).

Lepp, S. H.↗
NASA NTRS2014

Type Ia Supernova Rate Measurements to Redshift 2.5 from Candles: Searching for Prompt Explosions in the Early Universe

The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) was a multi-cycle treasury program on the Hubble Space Telescope(HST) that surveyed a total area of approx. 0.25 deg(sup 2) with approx.900 HST orbits spread across five fields over three years. Within these survey images we discovered 65 supernovae (SNe) of all types, out to z approx. 2.5. We classify approx. 24 of these as Type Ia SNe (SNe Ia) based on host galaxy redshifts and SN photometry (supplemented by grism spectroscopy of six SNe). Here we present a measurement of the volumetric SN Ia rate as a function of redshift, reaching for the first time beyond z = 2 and putting new constraints on SN Ia progenitor models. Our highest redshift bin includes detections of SNe that exploded when the universe was only approx. 3 Gyr old and near the peak of the cosmic star formation history. This gives the CANDELS high redshift sample unique leverage for evaluating the fraction of SNe Ia that explode promptly after formation (500 Myr). Combining the CANDELS rates with all available SN Ia rate measurements in the literature we find that this prompt SN Ia fraction isfP0.530.09stat0.100.10sys0.26, consistent with a delay time distribution that follows a simplet1power law for all timest40 Myr. However, mild tension is apparent between ground-based low-z surveys and space-based high-z surveys. In both CANDELS and the sister HST program CLASH (Cluster Lensing And Supernova Survey with Hubble), we find a low rate of SNe Ia at z > 1. This could be a hint that prompt progenitors are in fact relatively rare, accounting for only 20 of all SN Ia explosions though further analysis and larger samples will be needed to examine that suggestion.

Ia↗
DOE OSTI2022

Unravelling the extreme universe [Slides]

A journey to the early universe includes stops that examine the Quark Gluon plasma of the early universe 10 -6 seconds after the Big Bang and its extraordinary properties, the emergence of hadrons (like the proton and neutron) and light nuclei 1 second after the Big Bang, and the elusive neutrinos, in addition to the primordial ones that are also produced during star formation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

A sound horizon-free measurement of H 0 in DESI 2024

The physical size of the sound horizon at recombination is a powerful source of information for early-time measurements of the Hubble constant H 0 , and many proposed solutions to the Hubble tension therefore involve modifications to this scale. In light of this, there has been growing interest in measuring H 0 independently of the sound horizon. We present the first such measurement to use data from the Dark Energy Spectroscopic Instrument (DESI), jointly analyzing the full-shape galaxy power spectra of DESI luminous red galaxies, emission line galaxies, quasars, and the bright galaxy sample, in a total of six redshift bins. Information from the sound horizon scale is removed from our constraints via a rescaling procedure at the power spectrum level, with our sound horizon-marginalized measurement being driven instead primarily by the matter-radiation equality scale. This measurement is then combined with additional sound horizon-free information from Planck+ACT CMB lensing, uncalibrated type Ia supernovae, and the DESI Lyman-α forest. We agnostically combine with the DESY5, Pantheon+, and Union3 supernova datasets, with our tightest respective constraints being H 0 = 66.7 +1.7 -1.9 , 67.9 +1.9 -2.1 , and 67.8 +2.0 -2.2 km s -1 Mpc -1 . This corresponds to a sub-3% sound horizon-free constraint of the Hubble constant, and is the most precise measurement of its kind to date. Even without including information from the sound horizon, our measurement is still in 2.2-3.0σ tension with SH0ES. Additionally, the consistency between our result and other measurements that do rely on the sound horizon scale provides no evidence for new early-Universe physics (e.g. early dark energy). Future DESI data releases will allow unprecedented measurements of H 0 and place strong constraints on models that use beyond-ΛCDM physics to ameliorate the Hubble tension.

79 ASTRONOMY AND ASTROPHYSICS↗