Shedding Light On An Undiscovered Aspect That Perfectly Mimics Cosmic Acceleration

The comparison of redshift-distance relationship for high and low-redshift supernovae revealed the surprising transition of the Universe’s expansion from deceleration to acceleration. As compared to local supernovae, remote supernovae appear 10% to 25% dimmer as they are further away than expected. The expansion rate obtained for local supernovae is higher with low redshifts as compared to the expansion rate obtained for remote supernovae with high redshifts. Since observed redshifts in an expanding Universe provide an estimate of recession velocities, therefore, it is very disturbing to find that low recession velocities (just 1% of speed of light) indicate a faster rate of expansion (acceleration), whereas high recession velocities (60% of speed of light) indicate a slower rate of expansion (deceleration). In this paper, I unravel an undiscovered aspect that perfectly mimics cosmic acceleration. Rather than “cosmic deceleration that preceded the current epoch of cosmic acceleration”, I show in this paper, that “consecutive expansion epochs of the Universe that preceded the current epoch of cosmic expansion” were responsible for placing remote supernovae further away than expected. As a consequence of consecutive expansion, expansion began for remote structures in preceding expansion epochs before it did for local structures in the current (or more recent) expansion epoch; remote supernovae, quasars, and gamma-ray bursts are therefore not only further away than expected, but they also happen to yield a slower rate of expansion, thereby suggesting their deceleration even with “superluminal expansion”. As a result of consecutive expansion, preceding expansion epochs appear to be decelerating as compared to the expansion epoch that succeeds them. The analysis is based on the redshift-distance relationship plotted for 580 type Ia supernovae from the Supernova Cosmology Project, 7 additional high-redshift type Ia supernovae discovered through the Advanced Camera for Surveys on the Hubble Space Telescope from the Great Observatories Origins Deep Survey Treasury program, and 1 additional very high-redshift type Ia supernova discovered with Wide Field and Planetary Camera 2 on the Hubble Space Telescope. The results obtained by the High-Z Supernova Search Team through observations of type Ia supernovae have also been analysed. Studies incorporating quasars and gamma-ray bursts to determine how the expansion of the Universe has changed over time have been taken into consideration as well. The results obtained in this paper have been confirmed by plotting velocity-distance relationship, expansion rate vs. time relationship, expansion factor vs. time relationship, scale factor vs. time relationship, scale factor vs. distance relationship, distance-redshift relationship, and distance modulus vs. redshift relationship, moreover, the deceleration parameter (q0) is also found to be negative (q0 < 0).

Barrow Entropy Cosmology: an observational approach with a hint of stability analysis

In this work, we use an observational approach and dynamical system analysis to study the cosmological model recently proposed by Saridakis (2020), which is based on the modification of the entropy-area black hole relation proposed by Barrow (2020). The Friedmann equations governing the dynamics of the Universe under this entropy modification can be calculated through the gravity-thermodynamics conjecture. We investigate two models, one considering only a matter component and the other including matter and radiation, which have new terms compared to the standard model sourcing the late cosmic acceleration. A Bayesian analysis is performed in which using five cosmological observations (observational Hubble data, type Ia supernovae, HII galaxies, strong lensing systems, and baryon acoustic oscillations) to constrain the free parameters of both models. From a joint analysis, we obtain constraints that are consistent with the standard cosmological paradigm within 2σ confidence level. In addition, a complementary dynamical system analysis using local and global variables is developed which allows obtaining a qualitative description of the cosmology. As expected, we found that the dynamical equations have a de Sitter solution at late times.

Forbidden Line Emission from Type Ia Supernova Remnants Containing Balmer-dominated Shells

Balmer-dominated shells in supernova remnants (SNRs) are produced by collisionless shocks advancing into a partially neutral medium and are most frequently associated with Type Ia supernovae. We have analyzed Hubble Space Telescope (HST) images and Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) or AAT/Wide Field Integral Spectrograph observations of five Type Ia SNRs containing Balmer-dominated shells in the LMC: 0509–67.5, 0519–69.0, N103B, DEM L71, and 0548–70.4. Contrary to expectations, we find bright forbidden-line emission from small dense knots embedded in four of these SNRs. The electron densities in some knots are higher than 104 cm−3. The size and density of these knots are not characteristic for interstellar medium—they most likely originate from a circumstellar medium ejected by the SN progenitor. Physical property variations of dense knots in the SNRs appear to reflect an evolutionary effect. The recombination timescales for high densities are short, and HST images of N103B taken 3.5 yr apart already show brightness changes in some knots. VLT/MUSE observations detect [Fe xiv] line emission from reverse shocks into SN ejecta as well as forward shocks into the dense knots. Faint [O iii] line emission is also detected from the Balmer shell in 0519–69.0, N103B, and DEM L71. We exclude the postshock origin because the [O iii] line is narrow. For the preshock origin, we considered three possibilities: photoionization precursor, cosmic-ray precursor, and neutral precursor. We conclude that the [O iii] emission arises from oxygen that has been photoionized by [He ii] λ304 photons and is then collisionally excited in a shock precursor heated mainly by cosmic rays.

Masses of White Dwarf Binary Companions to Type Ia Supernovae Measured from Runaway Velocities

The recently proposed “dynamically driven double-degenerate double-detonation” (D6) scenario posits that Type Ia supernovae (SNe) may occur during dynamically unstable mass transfer between two white dwarfs (WDs) in a binary. This scenario predicts that the donor WD may then survive the explosion and be released as a hypervelocity runaway, opening up the exciting possibility of identifying remnant stars from D6 SNe and using them to study the physics of detonations that produce Type Ia SNe. Three candidate D6 runaway objects have been identified in Gaia data. The observable runaway velocity of these remnant objects represents their orbital speed at the time of SN detonation. The orbital dynamics and Roche lobe geometry required in the D6 scenario place specific constraints on the radius and mass of the donor WD that becomes the hypervelocity runaway. In this Letter, we calculate the radii required for D6 donor WDs as a function of the runaway velocity. Using mass–radius relations for WDs, we then constrain the masses of the donor stars as well. With measured velocities for each of the three D6 candidate objects based on Gaia EDR3, this work provides a new probe of the masses and mass ratios in WD binary systems that produce SN detonations and hypervelocity runaways.

ParSNIP: Generative Models of Transient Light Curves with Physics-enabled Deep Learning

We present a novel method to produce empirical generative models of all kinds of astronomical transients from data sets of unlabeled light curves. Our hybrid model, which we call ParSNIP, uses a neural network to model the unknown intrinsic diversity of different transients and an explicit physics-based model of how light from the transient propagates through the universe and is observed. The ParSNIP model predicts the time-varying spectra of transients despite only being trained on photometric observations. With a three-dimensional intrinsic model, we are able to fit out-of-sample multiband light curves of many different kinds of transients with model uncertainties of 0.04–0.06 mag. The representation learned by the ParSNIP model is invariant to redshift, so it can be used to perform photometric classification of transients even with heavily biased training sets. Our classification techniques significantly outperform state-of-the-art methods on both simulated (PLAsTiCC) and real (PS1) data sets with 2.3× and 2× less contamination, respectively, for classification of Type Ia supernovae. We demonstrate how our model can identify previously unobserved kinds of transients and produce a sample that is 90% pure. The ParSNIP model can also estimate distances to Type Ia supernovae in the PS1 data set with an rms of 0.150 ± 0.007 mag compared to 0.155 ± 0.008 mag for the SALT2 model on the same sample. We discuss how our model could be used to produce distance estimates for supernova cosmology without the need for explicit classification.

A Preliminary Calibration of the JAGB Method Using Gaia EDR3

The recently developed J-region asymptotic giant branch (JAGB) method has extraordinary potential as an extragalactic standard candle, capable of calibrating the absolute magnitudes of locally accessible Type Ia supernovae, thereby leading to an independent determination of the Hubble constant. Using Gaia Early Data Release 3 (EDR3) parallaxes, we calibrate the zero-point of the JAGB method, based on the mean luminosity of a color-selected subset of carbon-rich AGB stars. We identify Galactic carbon stars from the literature and use their near-infrared photometry and Gaia EDR3 parallaxes to measure their absolute J-band magnitudes. Based on these Milky Way parallaxes we determine the zero-point of the JAGB method to be M J = −6.14 ± 0.05 (stat) ± 0.11 (sys) mag. This Galactic calibration serves as a consistency check on the JAGB zero-point, agreeing well with previously published, independent JAGB calibrations based on geometric, detached eclipsing binary distances to the LMC and SMC. However, the JAGB stars used in this study suffer from the high parallax uncertainties that afflict the bright and red stars in EDR3, so we are not able to attain the higher precision of previous calibrations, and ultimately will rely on future improved DR4 and DR5 releases.

Near-infrared Supernova Ia Distances: Host Galaxy Extinction and Mass-step Corrections Revisited

We present optical and near-infrared (NIR, Y-, J-, H-band) observations of 42 Type Ia supernovae (SNe Ia) discovered by the untargeted intermediate Palomar Transient Factory survey. This new data set covers a broad range of redshifts and host galaxy stellar masses, compared to previous SN Ia efforts in the NIR. We construct a sample, using also literature data at optical and NIR wavelengths, to examine claimed correlations between the host stellar masses and the Hubble diagram residuals. The SN magnitudes are corrected for host galaxy extinction using either a global total-to-selective extinction ratio, R V = 2.0, for all SNe, or a best-fit R V for each SN individually. Unlike previous studies that were based on a narrower range in host stellar mass, we do not find evidence for a “mass step,” between the color- and stretch-corrected peak J and H magnitudes for galaxies below and above log ( M * / M ⊙ ) = 10 . However, the mass step remains significant (3σ) at optical wavelengths (g, r, i) when using a global R V , but vanishes when each SN is corrected using their individual best-fit R V . Our study confirms the benefits of the NIR SN Ia distance estimates, as these are largely exempted from the empirical corrections dominating the systematic uncertainties in the optical.

Cosmographic Parameters in Model-independent Approaches

The cosmographic approach, a Taylor expansion of the Hubble function, has been used as a model-independent method to investigate the evolution of the universe in the presence of cosmological data. Apart from possible technical problems like the radius of convergence, there is an ongoing debate about the tensions that appear when one investigates some high-redshift cosmological data. In this work, we consider two common data sets, namely, Type Ia supernovae (Pantheon sample) and the Hubble data, to investigate advantages and disadvantages of the cosmographic approach. To do this, we obtain the evolution of cosmographic functions using the cosmographic method, as well as two other well-known model-independent approaches, namely, the Gaussian process and the genetic algorithm. We also assume a ΛCDM model as the concordance model to compare the results of mentioned approaches. Our results indicate that the results of cosmography compared with the other approaches are not exact enough. Considering the Hubble data, which are less certain, the results of q 0 and j 0 obtained in cosmography provide a tension at more than 3σ away from the best result of ΛCDM. Assuming both of the data samples in different approaches, we show that the cosmographic approach, because it provides some biased results, is not the best approach for reconstruction of cosmographic functions, especially at higher redshifts.

The Foundation Supernova Survey: Photospheric Velocity Correlations in Type Ia Supernovae

The ejecta velocities of Type Ia supernovae (SNe Ia), as measured by the Si ii λ6355 line, have been shown to correlate with other supernova properties, including color and standardized luminosity. We investigate these results using the Foundation Supernova Survey, with a spectroscopic data release presented here, and photometry analyzed with the SALT2 light-curve fitter. We find that the Foundation data do not show significant evidence for an offset in color between SNe Ia with high and normal photospheric velocities, with Δc = 0.004 ± 0.015. Our SALT2 analysis does show evidence for redder high-velocity SNe Ia in other samples, including objects from the Carnegie Supernova Project, with a combined sample yielding Δc = 0.018 ± 0.008. When split on velocity, the Foundation SNe Ia also do not show a significant difference in Hubble diagram residual, ΔHR = 0.015 ± 0.049 mag. Intriguingly, we find that SN Ia ejecta velocity information may be gleaned from photometry, particularly in redder optical bands. For high-redshift SNe Ia, these rest-frame red wavelengths will be observed by the Nancy Grace Roman Space Telescope. Our results are in line with previous work that suggests SN Ia host-galaxy stellar mass is correlated with ejecta velocity: high-velocity SNe Ia are found nearly exclusively in high-stellar-mass hosts. However, host-galaxy properties alone do not explain velocity-dependent differences in supernova colors and luminosities across samples. Measuring and understanding the connection between intrinsic explosion properties and supernova environments, across cosmic time, will be important for precision cosmology with SNe Ia.