Tracing the story of the expansion of the Universe with Supernovae

Schematic representation of the expansion of the Universe over its history (Credit: NAOJ)

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An international research team analyzed a database of more than 1,000 supernova explosions and found that the expansion patterns of the Universe best match the data when a new time-dependent variation is introduced. If this turns out to be correct with better future data from the Subaru Telescope and other observatories, these results could point to as yet unknown physics working on a cosmic scale.

Edwin Hubble’s observations over 90 years ago showing the expansion of the Universe remain a cornerstone of modern astrophysics. But when you go into the details of calculating the speed of expansion of the Universe at different times in its history, scientists struggle to come up with theoretical models that match the observations.

To solve this problem, a team led by Maria Dainotti (assistant professor at the National Astronomical Observatory of Japan and the Graduate University for Advanced Studies, SOKENDAI in Japan and a scientist affiliated with the Space Science Institute in the United States) has analyzed a catalog of 1,048 supernovae that exploded at different times in the history of the Universe. The team found that theoretical models can be designed to match observations if one of the constants used in the equations, aptly called the Hubble constant, can change over time.

There are several possible explanations for this apparent change in the Hubble constant. A likely but annoying possibility is that there are observational biases in the data sample. To help correct for potential biases, astronomers use Hyper Suprime-Cam on the Subaru Telescope to observe paler supernovae over a wide area. The data from this instrument will increase the sample of supernovae observed in the early Universe and reduce the uncertainty of the data.

But if the current results stand up to further investigation, if the Hubble constant is in fact changing, it opens the question of what is driving the change. Answering this question might require a new, or at least modified, version of astrophysics.

These results will appear in MG Dainotti et al. “On the Hubble Constant Tension in the SNe Ia Pantheon Sample” in the Astrophysical Journal of May 17, 2021.

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