South Pole Telescope: should we review our understanding of the universe?
The South Pole Telescope (SPT) collaboration has just published the results of the telescope’s first two years of observations. The findings confirm the overall robustness of the Big Bang model, but also suggest that our model of the Universe may need revising. The results exacerbate the discrepancy between the cosmic microwave background and supernova explosions in regards to the expansion of the Universe. They also undermine the cosmological constant model by revealing a disparity with 3D galaxy maps. This analysis was carried out by a team led by Silvia Galli at the Institut d’astrophysique de Paris (IAP - Sorbonne University/CNRS), with support from the ERC NEUCosmoS project. Their results have been published in the journal Physical Review D.
Located at the US Antarctic base, the telescope is equipped with a third-generation camera (SPT-3G). The camera produces sky maps of unrivalled precision and sensitivity. These maps improve upon observations of the cosmic microwave background - the first light in the Universe, previously produced by the European Planck satellite telescope and recent observations from the ACT telescope located in the Atacama Desert (Chile).
Analysing these maps required numerous methodological innovations and confirms the discrepancies between background radiation data and observations of supernova explosions regarding the measurement of the expansion of the Universe. By combining all available data, it is possible that a new model of the Universe could reconcile the various observations made to date.
At the turn of the 21st century, astronomers demonstrated that the expansion of the Universe was accelerating due to the effect of dark energy. This launched ambitious projects to create three-dimensional maps of the positions of billions of galaxies, such as the DESI ground-based observation programme and the European space telescope Euclid.
A recent analysis of the DESI maps points to a form of dark energy that differs from the simple cosmological constant model. A comparison of the cosmic background radiation measurements provided by SPT, Planck and ACT with the DESI maps suggests that a model with a cosmological constant may no longer be sufficient to account for the observations available to astronomers.
Although the studies carried out by the South Pole Telescope team do not yet allow us to determine which alternative model will reconcile all the observations, the future will undoubtedly shed more light on the matter. The current analysis of the SPT’s cameras covers only 20% of the quarter of the sky that the project intends to observe. Furthermore, the DESI programme has analysed only three years of data and plans to continue observing the sky for at least another two years. Finally, the European Euclid satellite will deliver its first cosmological data in late 2026.
In conclusion, it appears that we are merely at the dawn of a new era of inquiry into our cosmological model.
- For further information:
Link to the article published in the Physical Review D. - Link to the complementary article on the results, published on the IAP’s website
- More information on the results by the University of Chicago, which is leading the South Pole Telescope project and its SPT-3G camera