Exceptional supernova to help resolve "Hubble tension"
Cosmology is puzzled as to why two methods for measuring the expansion of the cosmos yield different results. A third method is now expected to help.
The two foreground galaxies (in yellow) and the supernova five times (in blue)
(Image: © SN Winny Research Group)
A supernova, whose light reaches us via five paths thanks to two gravitational lenses, is intended to help calculate the expansion speed of the universe and thus resolve the “Hubble tension”. This was announced by Ludwig Maximilian University of Munich, where the research into the stellar explosion is being led. It is a unique find, “the probability of finding a superluminous supernova located exactly behind a gravitational lens is less than one in a million,” explains cosmologist Sherry Suyu, who is involved in the work. The research group has named the supernova “SN Winny”, after its official designation, SN 2025wny. It is currently being intensively observed.
Extreme stroke of luck for cosmology
The supernova is about ten billion light-years away; it is “a rare, superluminous stellar explosion”, the team further explains. This makes it far brighter than ordinary supernovae, which already helps in research. The two foreground galaxies are responsible for the extraordinary circumstance that we see it multiple times. Their mass warps the light on its way through the cosmos, which is why it comes to us from five directions. Because the paths are of different lengths, this happens with a time delay, and precisely from these differences “the current expansion rate of the universe – the Hubble constant – can be determined”. The event could thus “play a key role in our understanding of the cosmos”, says Suyu.
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The research team explains that they now need to know the exact mass distribution in the two foreground galaxies to accurately determine the Hubble constant from the time difference between the incoming signals. This means that this method is based on fewer, but “completely different” sources of systematic uncertainty. However, they first had to confirm that all five signals actually came from the same supernova. The research group is confident that their work will “provide crucial new insights” and help to finally resolve the so-called Hubble tension. Two scientific papers are now available in advance.
The “Hubble tension” refers to an ever-increasing discrepancy in the value of the Hubble constant that has puzzled cosmology for years. The Hubble constant (H0) is a fundamental quantity in cosmology. Its value indicates the speed at which an object at a distance of one megaparsec (3.26 million light-years) is moving away from us solely due to the expansion of the universe. The constant was first calculated by the US astronomer Edwin Hubble, after whom it is now named. Measurements in the relatively nearby universe yield a significantly different value for the constant than high-precision measurements from the epoch immediately after the Big Bang. The researchers from Germany now want to help clarify this with their third method.
(mho)
