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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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NASA NTRS1992

Interpretation of the cosmic microwave background radiation anisotropy detected by the COBE Differential Microwave Radiometer

The large-scale cosmic background anisotropy detected by the COBE Differential Microwave Radiometer (DMR) instrument is compared to the sensitive previous measurements on various angular scales, and to the predictions of a wide variety of models of structure formation driven by gravitational instability. The observed anisotropy is consistent with all previously measured upper limits and with a number of dynamical models of structure formation. For example, the data agree with an unbiased cold dark matter (CDM) model with H0 = 50 km/s Mpc and Delta-M/M = 1 in a 16 Mpc radius sphere. Other models, such as CDM plus massive neutrinos (hot dark matter (HDM)), or CDM with a nonzero cosmological constant are also consistent with the COBE detection and can provide the extra power seen on 5-10,000 km/s scales.

Wright, E. L.↗
NASA NTRS1981

Anisotropy of the cosmic microwave background radiation

Theoretical predictions of the angular anisotropy in the cosmic microwave background radiation on both small and large angular scales are presented, and the effect of massive neutrinos on both the background radiation anisotropy and on the galaxy correlation function over very large scales is reviewed. Current observations show that the quadrupole anisotropy provides the greatest constraint on theory, and the values for the gravitational potential fluctuations indicate that small amplitude but sufficiently large-scale density fluctuations, both at the present epoch and on the surface of last scattering, can produce significant large angular scale variations in the radiation temperature. Most importantly, it is proposed that the quadrupole moment is most simply and elegantly interpreted in terms of the density fluctuations on very large scales whose presence is inferred from the requirement that an initial fluctuation spectrum is required in order for structure to develop.

Silk, J.↗
NASA NTRS1990

A search for anisotropy in the cosmic microwave radiation at medium angular scales

The results are reported from a search for anisotropy in the cosmic microwave radiation (CMR) at angular scales of 0.5 to 5 deg. No temperature fluctuations are detected, and limits are placed on intrinsic CMR anisotropy. These limits are expressed in terms of two models which describe the temperature fluctuations. For models specified by a Gaussian-shaped correlation function, the fluctuation amplitude is found to be 1.1 x 10 to the -4th or less at 1.1 deg; for models with monochromatic fluctuations it is 7.5 x 10 to the -5th or less at 1.7 deg. These limits satisfy the likelihood ratio test at the 95 percent confidence level. The implications of the results for large-scale structure information scenarios are discussed.

Timbie, Peter T.↗
NASA NTRS1994

The amplitude and spectral index of the large angular scale anisotropy in the cosmic microwave background radiation

In many cosmological models, the large angular scale anisotropy in the cosmic microwave background is parameterized by a spectral index, n, and a quadrupolar amplitude, Q. For a Harrison-Peebles-Zel'dovich spectrum, n = 1. Using data from the Far Infrared Survey (FIRS) and a new statistical measure, a contour plot of the likelihood for cosmological models for which -1 less than n less than 3 and 0 equal to or less than Q equal to or less than 50 micro K is obtained. Depending upon the details of the analysis, the maximum likelihood occurs at n between 0.8 and 1.4 and Q between 18 and 21 micro K. Regardless of Q, the likelihood is always less than half its maximum for n less than -0.4 and for n greater than 2.2, as it is for Q less than 8 micro K and Q greater than 44 micro K.

Ganga, Ken↗
NASA NTRS1992

A bolometric millimeter-wave system for observations of anisotropy in the cosmic microwave background radiation on medium angular scales

The performance of a bolometric system designed to measure the anisotropy of the cosmic microwave background (CMB) radiation on angular scales from 0.3 to 3 deg is presented. The system represents a collaborative effort combining a low-background 1-m diameter balloon-borne telescope with new multimode feed optics, a beam modulation mechanism with high stability, and a four-channel bolometric receiver with passbands centered near frequencies of 3, 6, 9, and 12/cm (90, 180, 270, and 360 GHz). The telescope has been flown three times with the bolometric receiver and has demonstrated detector noise limited performance capable of reaching sensitivity levels of about 0.00001 with detectors operated at 0.3 K.

Fischer, M. L.↗
NASA NTRS1994

A measurement of the medium-scale anisotropy in the cosmic microwave background radiation

Observations from the first flight of the Medium Scale Anisotropy Measurement (MSAM) are analyzed to place limits on Gaussian fluctuations in the cosmic microwave background radiation (CMBR). This instrument chops a 30 min beam in a three-position pattern with a throw of +/- 40 min; the resulting data is analyzed in statistically independent single- and double-difference sets. We observe in four spectral channels at 5.6, 9.0, 16.5, and 22.5/cm, allowing the separation of interstellar dust emission from CMBR fluctuations. The dust component is correlated with the IRAS 100 micron map. The CMBR component has two regions where the signature of an unresolved source is seen. Rejecting these two source regions, we obtain a detection of fluctuations which match CMBR in our spectral bands of 0.6 x 10(exp -5) is less than Delta (T)/T is less than 2.2 x 10(exp -5) (90% CL interval) for total rms Gaussian fluctuations with correlation angle 0.5 deg, using the single-difference demodulation. Fore the double difference demodulation, the result is 1.1 x 10(exp -5) is less than Delta(T)/T is less than 3.1 x 10(exp -5) (90% CL interval) at a correlation angle of 0.3 deg.

Cheng, E. S.↗
NASA NTRS1981

The cosmic microwave background radiation

Because angular anisotropies and spectral distortions of the cosmic microwave background radiation are judged to be inevitable at some level, in a realistic cosmological model, the evidence for spectral distortions and its theoretical implications are described. The evidence for anisotropy is then discussed, and theoretical predictions of radiation anisotropy are summarized and compared with the data available. It is found that spectral distortions at the 3-sigma level near the peak of the blackbody spectrum, although inconsistent with the predicted distortions due to Compton scattering in the early universe, are elegantly interpreted in terms of radiation from an early, pregalactic generation of massive stars which had been thermalized by a modest amount of dust at high redshift. The quadrupole anisotropy at the 4-sigma level is most simply interpreted in terms of the large-scale structure of the universe.

Silk, J.↗
NASA NTRS1992

A bolometric millimeter-wave system for observations of anisotropy in the cosmic microwave background radiation on medium angular scales

We report the performance of a bolometric system designed to measure the anisotropy of the cosmic microwave background (CMB) radiation on angular scales from 0 deg 3 min to 3 deg. The system represents a collaborative effort combining a low-background 1 m diameter balloon-borne telescope with new multimode feed optics, a beam modulation mechanism with high stability, and a four-channel bolometric receiver with passbands centered near frequencies of 3 (90), 6 (180), 9 (270), and 12 (360) cm(exp -1) (GHz). The telescope was flown three times with the bolometric receiver and has demonstrated detector noise limited performance capable of reaching sensitivity levels of Delta(T)/T(sub CMB) is approximately equal to 10(exp -5) with detectors operated at T = 0.3 K.

Fischer, M. L.↗
NASA NTRS1979

Southern Hemisphere measurements of the anisotropy in the cosmic microwave background radiation

A recent airborne measurement of the large-angular-scale anisotropy in the cosmic background radiation from the Southern Hemisphere (Lima, Peru) is in essential agreement with previous measurements from the northern hemisphere. The net anisotropy from the combined data can be described by a first-order spherical harmonic (Doppler) anisotropy of amplitude 3.1 plus or minus 0.4 mK with a quadrupole component of less than 1 mK. Additional ground-based measurements of the linear polarization yield an upper limit of l mK, or one part in 3000, at 95% confidence level for the amplitudes of any spherical harmonic through third order.

Smoot, G. F.↗
NASA NTRS1981

Large-scale anisotropy of the cosmic microwave background radiation

Inhomogeneities in the large-scale distribution of matter inevitably lead to the generation of large-scale anisotropy in the cosmic background radiation. The dipole, quadrupole, and higher order fluctuations expected in an Einstein-de Sitter cosmological model have been computed. The dipole and quadrupole anisotropies are comparable to the measured values, and impose important constraints on the allowable spectrum of large-scale matter density fluctuations. A significant dipole anisotropy is generated by the matter distribution on scales greater than approximately 100 Mpc. The large-scale anisotropy is insensitive to the ionization history of the universe since decoupling, and cannot easily be reconciled with a galaxy formation theory that is based on primordial adiabatic density fluctuations.

Silk, J.↗
NASA NTRS1994

Measurements of anisotropy in the cosmic microwave background radiation at degree angular scales near the stars Sigma Herculis and Iota Draconis

We present results from two four-frequency observations centered near the stars Sigma Herculis and Iota Draconis during the fourth flight of the Millimeter-wave Anisotropy eXperiment (MAX). The observations were made of 6 deg x 0.6 deg strips of the sky with a 1.4 deg peak to peak sinusoidal chop in all bands. The full width at half maximum (FWHM) beam sizes were calculated 0.55 deg +/- 0.05 deg at 3.5/cm and a 0.75 deg +/- 0.05 deg at 6, 9, and 14/cm. Significant correlated structures were observed at 3.5, 6, and 9/cm. The spectra of these signals are inconsistent with thermal emission from known interstellar dust populations. The extrapolated amplitudes of synchrotron and free-free emission are too small to account for the amplitude of the observed structures. If the observed structures are attributed to cosmic microwave background (CMB) anisotropy with a Gaussian autocorrelation function and a coherence angle of 25 min, then the most probable values at Delta T/T(sub CMB) = 3.1 (sup +1.7 sub -1.3) x 10(exp -5) for the Sigma Herculis scan, and Delta T/T(sub CMB) = 3.3(sup +1.1 sub -1.1) x 10(exp -5) for the Iota Draconis scan (95% confidence upper, lower limits).

Clapp, A. C.↗
NASA NTRS1992

The implications of the COBE diffuse microwave radiation results for cosmic strings

We compare the anisotropies in the cosmic microwave background radiation measured by the COBE experiment to those predicted by cosmic string theories. We use an analytic model for the Delta T/T power spectrum that is based on our previous numerical simulations of strings, under the assumption that cosmic strings are the sole source of the measured anisotropy. This implies a value for the string mass per unit length of 1.5 +/- 0.5 x 10 exp -6 C-squared/G. This is within the range of values required for cosmic strings to successfully seed the formation of large-scale structures in the universe. These results clearly encourage further studies of Delta T/T and large-scale structure in the cosmic string model.

Bennett, David P.↗
NASA NTRS1977

Translational anisotropy in the cosmic microwave background radiation and far-infrared emission by galactic dust clouds

The predicted emission spectrum of galactic dust at about 10 K is compared with the spectrum of 2.8-K universal blackbody radiation and with the spectrum of the anisotropy expected in the 2.8-K radiation due to motion of earth with respect to the coordinate system in which the radiation was last scattered. The extremely anisotropic galactic-dust emission spectrum may contribute a significant background to anisotropy measurements which scan through the galactic plane. The contamination would appear in an 8-mm scan around the celestial equator, for example, as a spurious 200 km/s velocity toward declination 0 deg, right ascension 19 hr, if predictions are correct. The predicted spectrum of dust emission in the galactic plane at longitudes not exceeding about 30 deg falls below the total 2.8-K cosmic background intensity at wavelengths of at least 1 mm.

Forman, M. A.↗
NASA NTRS1994

Measurements of anisotropy in the cosmic microwave background radiation at 0.5 deg angular scales near the star gamma ursae minoris

We present results from a four-frequency observation of a 6 deg x 0.6 deg strip of the sky centered near the star Gamma Ursae Minoris (GUM) during the fourth flight of the Millimeter-wave Anistropy experiment(MAX). The observation was made with a 1.4 deg peak-to-peak sinusoidal chop in all bands. The FWHM beam sizes were 0.55 deg +/- 0.05 deg at 3.5 per cm and 0.75 deg +/- 0.05 deg at 6, 9, and 14 per cm. During this observation significant correlated structure was observed at 3.5, 6 and 9 per cm with amplitudes similar to those observed in the GUM region during the second and third fligts of MAX. The frequency spectrum is consistent with cosmic microwave background (CMB) and inconsistent with thermal emission from interstellar dust. The extrapolated amplitudes of synchrotron and free-free emission are too small to account for the amplitude of the observed structure, If all of the structure is attributed to CMB anisotropy with a Gaussian autocorrelation function and a coherence angle of 25 min, then the most probable values of delta T/T(sub CMB) in the 3.5, 6 and 9 per cm bads are (4.3 +2.7/-1.6) x 10(exp -5), 2.8 (+4.3/-1/1) x 10(exp -5), and 3.5 (+3.0/-1.6) x 10(exp -5) (95% confidence upper and lower limits), respectively.

Devlin, M. J.↗
NASA NTRS1991

First results of the COBE satellite measurement of the anisotropy of the cosmic microwave background radiation

The concept and operation of the Differential Microwave Radiometers (DMR) instrument aboard NASA's Cosmic Background Explorer satellite are reviewed, with emphasis on the software identification and subtraction of potential systematic effects. Preliminary results obtained from the first six months of DMR data are presented, and implications for cosmology are discussed.

Smoot, G. F.↗
NASA NTRS1998

Anisotropy of the Cosmic Microwave Background Radiation on Large and Medium Angular Scales

This grant has supported work at Brown University on measurements of the 2.7 K Cosmic Microwave Background Radiation (CMB). The goal has been to characterize the spatial variations in the temperature of the CMB in order to understand the formation of large-scale structure in the universe. We have concurrently pursued two measurements using millimeter-wave telescopes carried aloft by scientific balloons. Both systems operate over a range of wavelengths, chosen to allow spectral removal of foreground sources such as the atmosphere, Galaxy, etc. The angular resolution of approx. 25 arcminutes is near the angular scale at which the most structure is predicted by current models to be visible in the CMB angular power spectrum. The main goal is to determine the angular scale of this structure; in turn we can infer the density parameter, Omega, for the universe as well as other cosmological parameters, such as the Hubble constant.

Houghton, Anthony↗
DOE OSTI2025

Cosmic recombination in the presence of primordial magnetic fields

Primordial magnetic fields (PMFs) may explain observations of magnetic fields on extragalactic scales. They are most cleanly constrained by measurements of cosmic microwave background radiation (CMB) anisotropies. Their effects on cosmic recombination may even be at the heart of the resolution of the Hubble tension. We present the most detailed analysis of the effects of PMFs on cosmic recombination to date. To this end we extend the public magneto-hydrodynamic code ENZO with a new cosmic recombination routine, Monte-Carlo simulations of Lyman-α photon transport, and a Compton drag term in the baryon momentum equation. The resulting code allows us, for the first time, to realistically predict the impact of PMFs on the cosmic ionization history and the clumping of baryons during cosmic recombination. Our results identify the importance of mixing of Lyman-α photons between overdense- and underdense- regions for small PMF strength. This mixing speeds up recombination beyond the speed-up due to clumping. We also investigate the effects of pecuilar flows on the recombination rate and find it to be small for small PMF strengths. For non-helical PMFs with a Batchelor spectrum we find a surprising dependency of results on ultra-violet magnetic modes. We further show that the increase in the ionization fraction at low redshift by hydrodynamic baryon heating due to PMF dissipation is completely compensated by the faster recombination from baryon clumping. In conclusion, the present study shall serve as a theoretical foundation for a future precise comparison of recombination with PMFs to CMB data.

79 ASTRONOMY AND ASTROPHYSICS↗