Title: Can rotation solve the Hubble puzzle?
Authors: Balázs Endre Szigeti, István Szapudi, Imre Ferenc Barna, and Gergely Gábor Barnaföldi
First Author’s Institution: Institute of Physics, Eötvös Loránd University, 11/A Pázmány Péter Stny, Budapest H-1117, Hungary
Status: Published in MNRAS [open access]
Replicability is key to science. Checking if different experimental methods yield the same result can tell us whether that result is real, or merely a fluke. That’s why measurements of the Universe’s expansion rate, or the Hubble constant (H0), are so perplexing – there’s a discrepancy between the values of H0 determined by two different self-consistent measurement techniques known as the Hubble tension. This discrepancy is illustrated in Figure 1, which shows the H0 values determined by various experiments employing the two techniques. One technique uses the redshift of spectroscopic observations of Type Ia supernovae (SNe) in the late Universe to determine how fast galaxies are receding from each other. A recent study of observations from the Hubble Space Telescope suggests that the Hubble constant is HSNe=73.04 ±1.07 kms-1Mpc-1. Another way to determine H0 is to effectively look back in time by observing the earliest light emitted in the Universe, the cosmic microwave background (CMB), and fitting to its spectrum.
Most objects in the Universe are observed to be rotating: planets, stars, galaxies, black holes – the list goes on! So, it seems logical to think that the Universe itself could be rotating, too. In fact, researchers have come up with cosmological models where the Universe is the interior of a rotating black hole. Today’s authors construct a mathematical model for a Universe rotating with an angular velocity ω and demonstrate how H0 is affected. They calculated the values of H0 that their model predicts as a function of ω, which is shown plotted in Figure 2. The black points show their calculations, while the solid and dashed gray curve shows the interpolation and extrapolation of those points. The horizontal bands between the blue and orange dashed lines denote the values of HSNe and HCMB with their uncertainty ranges. By looking at the parts of the gray curve that fall within these bands, the authors can identify the value of ω in the early (HCMB band) and late (HSNe band) Universe. The red shading denotes values of ω that exceed the upper limit based on the constraint that speeds cannot exceed the speed of light in the observable Universe. They find that the present-day angular velocity ω0 to be 0.002 rotations/billion years (which is close to the maximum value) and the angular velocity at the time the CMB was emitted ωCMB to be 0.0004 rotations/billion years*. This suggests that the Universe has been rotating faster over time, which could support the idea that the Universe is the interior of a black hole because as black holes accrete mass over time, they spin faster.
Although this paper’s results appear to be a promising step forward in resolving the Hubble tension, the authors note that they have only investigated the effects of their rotating Universe on H0, and further work is needed to explore how other cosmological parameters are affected. For now, we can continue puzzling over this problem as we eagerly await future results.
*The value of ωCMB the authors quote in their paper appears to be a typo based on Figure 2 in their paper. For this article, I have assumed the value of ωCMB based on Figure 2 in their paper.
Astrobite edited by Catherine Slaughter
Featured image credit: Adapted from NASA/WMAP Science Team/ Art by Dana Berry
