Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant

Abstract

We present spectral and photometric observations of 10 type Ia supernovae (SNe Ia) in the redshift range 0.16 ≤ z ≤ 0.62. The luminosity distances of these objects are determined by methods that employ relations between SN Ia luminosity and light curve shape. Combined with previous data from our High-Z Supernova Search Team (Garnavich et al. 1998;Schmidt et al. 1998) and Riess et al. (1998a), this expanded set of 16 high-redshift supernovae and a set of 34 nearby supernovae are used to place constraints on the following cosmological parameters: the Hubble constant (H 0 ), the mass density (Ω M ), the cosmological constant (i.e., the vacuum energy density, Ω Λ ), the deceleration parameter (q 0 ), and the dynamical age of the Universe (t 0 ). The distances of the high-redshift SNe Ia are, on average, 10% to 15% farther than expected in a low mass density (Ω M = 0.2) Universe without a cosmological constant. Different light curve fitting methods, SN Ia subsamples, and prior constraints unanimously favor eternally expanding models with positive cosmological constant (i.e., Ω Λ > 0) and a current acceleration of the expansion (i.e., q 0 < 0). With no prior constraint on mass density other than Ω M ≥ 0, the spectroscopically confirmed SNe Ia are statistically consistent with q 0 < 0 at the 2.8σ -2and 3.9σ confidence levels, and with Ω Λ > 0 at the 3.0σ and 4.0σ confidence levels, for two different fitting methods respectively. Fixing a "minimal" mass density, Ω M = 0.2, results in the weakest detection, Ω Λ > 0 at the 3.0σ confidence level from one of the two methods. For a flat-Universe prior (Ω M + Ω Λ = 1), the spectroscopically confirmed SNe Ia require Ω Λ > 0 at 7σ and 9σ formal significance for the two different fitting methods. A Universe closed by ordinary matter (i.e., Ω M = 1) is formally ruled out at the 7σ to 8σ confidence level for the two different fitting methods. We estimate the dynamical age of the Universe to be 14.2 ±1.5 Gyr including systematic uncertainties in the current Cepheid distance scale. We estimate the likely effect of several sources of systematic error, including progenitor and metallicity evolution, extinction, sample selection bias, local perturbations in the expansion rate, gravitational lensing, and sample contamination. Presently, none of these effects reconciles the data with Ω Λ = 0 and q 0 ≥ 0.

A Possible Alternative to the Accelerating Universe III

“…In two previous works by the author [1] [2], hereafter referred to as I and II, it was shown that it is possible to explain the diminished brightness of the Type Ia supernovae (SNe Ia) found by Perlmutter et al [3] [4], Riess et al [5], and Schmidt et al [6], and the increased distance to the "standard ruler" of the baryon acoustic oscillations (BAO) determined by Anderson et al [7] [8], by assuming that the speed of light through the dark energy of intergalactic space has been reduced to c/n, where n is the index of refraction of the dark energy. Thus, in this alternative model, the dark energy no longer has associated with its energy-momentum source tensor a negative pressure that causes the expansion of the universe to accelerate (for a review see, e.g., Wang [9]), but instead has an index of refraction greater than unity.…”

Revamping Newtonian Gravity

“…Note that although the title of van den Bergh's 1999 paper is The Early History of Dark Matter, the century long search for Vulcan is entirely overlooked. The most recent purported evidence for dark matter, starting in the last decade of the twentieth century and continuing vigorously today, comes from detailed surveys and analyses of Type Ia supernovae (SNe Ia) [8]- [13] and cosmic microwave background (CMB) anisotropies [7].…”

Astrophysical explosions: from solar flares to cosmic gamma-ray bursts

“…The supernova distance determined in this way is independent of the recession velocity as determined by the redshift of the host galaxy. These two independent pieces of information, applied statistically to a large sample of type Ia supernovae, revealed the remarkable, and deeply challenging, result that the Universe is accelerating, most often interpreted as the effect of a 'dark energy' [48,49]. The supernova results coupled with other techniques (fluctuations in the cosmic microwave background radiation, the spatial distributions of galaxies and the growth of clusters of galaxies) suggest that this effect is consistent with Einstein's cosmological constant in a Universe that is geometrically flat.…”