The Dark Energy Survey Supernova Program: Slow supernovae show cosmological time dilation out to $z \sim 1$ (2406.05050v2)

Abstract: We present a precise measurement of cosmological time dilation using the light curves of 1504 type Ia supernovae from the Dark Energy Survey spanning a redshift range $0.1\lesssim z\lesssim 1.2$. We find that the width of supernova light curves is proportional to $(1+z)$, as expected for time dilation due to the expansion of the Universe. Assuming type Ia supernovae light curves are emitted with a consistent duration $\Delta t_{\rm em}$, and parameterising the observed duration as $\Delta t_{\rm obs}=\Delta t_{\rm em}(1+z)^b$, we fit for the form of time dilation using two methods. Firstly, we find that a power of $b \approx 1$ minimises the flux scatter in stacked subsamples of light curves across different redshifts. Secondly, we fit each target supernova to a stacked light curve (stacking all supernovae with observed bandpasses matching that of the target light curve) and find $b=1.003\pm0.005$ (stat) $\pm\,0.010$ (sys). Thanks to the large number of supernovae and large redshift-range of the sample, this analysis gives the most precise measurement of cosmological time dilation to date, ruling out any non-time-dilating cosmological models at very high significance.

• The paper precisely measures cosmological time dilation by analyzing 1504 Type Ia supernovae light curves from DES, confirming Einstein's (1+z) prediction.
• It employs dual methods—flux scatter minimization and light curve stacking—to achieve a measurement of b = 1.003 ± 0.005 independent of model assumptions.
• The findings advance cosmological research by ruling out non-time-dilating models and paving the way for higher precision analyses with future surveys.

Cosmological Time Dilation Measured Using DES Supernovae

The paper "The Dark Energy Survey Supernova Program: Slow supernovae show cosmological time dilation out to $z\sim1$" presents a precise measurement of cosmological time dilation by analyzing the light curves of 1504 Type Ia supernovae from the Dark Energy Survey (DES). These supernovae span a redshift range from approximately $0.1$ to $1.2$. The paper confirms a fundamental prediction of Einstein's theory of relativity in an expanding Universe: the observed duration of an event should be longer than its intrinsic emitted duration by a factor of $(1+z)$ due to time dilation.

Method and Analysis

The authors undergo a dual-method approach to measure the time dilation effect. The first method involves observing the flux scatter in the stacked subsamples of light curves across various redshifts to determine the power $b$ that minimizes this scatter. Here, they find a power of $b \approx 1$, aligning with the theoretical expectation for cosmological time dilation. In the second method, they fit each supernova to a reference light curve derived from stacking and time-shifting all supernovae within similar observed bandpasses. This method yields a very precise measurement with $b=1.003\pm0.005$ (statistical) and an additional systemic error of $\pm0.010$.

Both methods have been designed to remain independent of supernova modeling assumptions, a significant shift from previous approaches that often incorporated model-dependent analyses. As an outcome, the paper rules out any non-time-dilating cosmological models and asserts $(1+z)$ time dilation with an unmatched precision to date.

Implications

The findings have several implications for both theoretical and observational astrophysics:

• Theoretical Confirmation: The results provide robust observational support for the standard model of cosmology that assumes an expanding universe governed by general relativity.
• Methodology Advancement: The paper demonstrates the capability of leveraging vast datasets for analyses that minimize reliance on model-dependent methods. This advancement can improve the reliability and precision of future cosmological measurements.
• Data Utilization: By employing the large and diverse dataset from the DES, the paper exemplifies how extensive observational campaigns can enhance our understanding of fundamental cosmological parameters.

Future Directions

The authors suggest that their methods could be applied to even larger datasets or extended to higher redshift ranges, should future surveys provide the necessary data. The increase in precision could further cement our current cosmological model or identify any small deviations that might hint at new physics.

Overall, this paper contributes significantly to establishing the reliability of time dilation as an observational phenomenon that supports the cosmological principle of an expanding universe. Such comprehensive data-driven methodologies open avenues for continued exploration in cosmology, potentially bridging observations with refined theoretical models.