A new study once again shows that the universe is expanding faster than calculated in previous years. This research, this time conducted by astronomers from the University of California at Davis, only further increases the debate about the fact that we cannot measure the acceleration of the universe’s expansion with a good degree of precision: the measurements made in recent years are in fact in disagreement.
This time the researchers used the Hubble Space Telescope together with an instrument from the WM Keck observatory called Adaptive Optics (AO). With this tool, researchers have been able to exploit the so-called “gravitational lenses,” a phenomenon also predicted by Einstein in which even light is gravitationally attracted and when this happens it can, among other things, also enlarge objects too far away for be viewed with normal telescopes. In the new study, which appeared in the Monthly Notices of the Royal Astronomical Society, the researchers performed measurements of three known quasars with the gravitational lens method: PG1115 + 080, HE0435-1223 and RXJ1131-1231.
In particular, they measured the flicker of their brightness. These flickers, since each image corresponds to a slightly different length of the quasar distance from the telescope, do not all arrive on Earth at the same time. The researchers accurately measured these delays because they are inversely proportional to the value of the Hubble constant indicating the rate of expansion of the universe. In this way, they were able to measure how much the universe expanded during the time when the light of these quasars headed for Earth. The results they obtained are consistent with some measurements of the same Hubble constant made by observing objects near Earth, such as supernovae or other systems with gravitational lenses.
These further measurements highlight that there is a problem with the standard model of cosmology. This model predicts that the universe has expanded very rapidly during the big bang, or in any case immediately thereafter, and that this expansion has then slowed down, perhaps due to the gravitational attraction of dark matter. At some point, the same rate of expansion began to accelerate again this time due to a new force called dark energy. This model is mainly based on the analysis of the cosmic microwave background (CMB), that is, on the residual radiation of the big bang that occurred about 13.8 billion years ago.
Recently several attempts to measure the Hubble constant have led to inconsistent results, especially as regards measurements made by observing objects close to those made by observing distant objects.
“This is where the crisis in cosmology lies,” says physics professor Chris Fassnacht and one of the authors of the study. “While the Hubble constant is constant everywhere in space at any given moment, it is not constant over time. So when we compare by comparing the Hubble constants that result from various techniques, we are comparing the primordial universe (using distant observations) vs the later and more modern part of the universe (using local and close observations).”
There are two possibilities: either there is a problem with the CMB measurements, the cosmic background radiation in the microwaves, which the researchers behind this study consider unlikely, or the standard model must be modified in order for this discrepancy to be corrected.
Now the researchers intend to further develop this new method, based on gravitational lenses and quasar observation, to further improve the accuracy of the Hubble constant measurements to perhaps reach a more “universal” cosmological model.