NASA's latest supernova image could tell us how fast the universe is expanding

The James Webb Space Telescope's Near-Infrared Camera (NIRCam) captured a curious sight in a region 3.6 billion light-years away from Earth: A supernova that appears three times, at three different periods during its explosion, in one image. More importantly, this image could help scientists better understand how fast the universe is expanding. 

A team of researchers chose to observe the galaxy cluster PLCK G165.7+67.0, also known as G165, for its high star rate formation that also leads to higher supernova rates. One image, which you can see above, captures what looks to be a streak of light with three distinct dots that appear brighter than the rest of it. As Dr. Brenda Frye from the University of Arizona explained, those dots correspond to an exploding white dwarf star. It is also gravitationally lensed — that is, there's a cluster of galaxies between us and the star that served as a lens, bending the supernova's light into multiple images. Frye likened it to a trifold mirror that shows a different image of the person sitting in front of it. To note, it is the most distant Type Ia supernova, which is a supernova that occurs in a binary system, observed to date.

Because of that cluster of galaxies in front of the supernova, light from the explosion travelled three different paths, each with a different length. That means the Webb telescope was able to capture different periods of its explosion in one image: Early into the event, mid-way through and near the end of it. Trifold supernova images are special, Frye said, because the "time delays, supernova distance, and gravitational lensing properties yield a value for the Hubble constant or H0 (pronounced H-naught)." 

NASA describes the Hubble constant as the number that characterizes the present-day expansion rate of the universe, which, in turn, could tell us more about the universe's age and history. Scientists have yet to agree on its exact value, and the team is hoping that this supernova image could provide some clarity. "The supernova was named SN H0pe since it gives astronomers hope to better understand the universe's changing expansion rate," Frye said. 

Wendy Freedman from the University of Chicago led a team in 2001 that found a value of 72. Other teams put the Hubble constant between 69.8 and 74 kilometers per second per megaparsec. Meanwhile, this team reported a value of 75.4, plus 8.1 or minus 5.5. "Our team’s results are impactful: The Hubble constant value matches other measurements in the local universe, and is somewhat in tension with values obtained when the universe was young," Frye said. The supernova and the Hubble constant value derived from it need for be explored further, however, and the team expects future observations to "improve on the uncertainties" for a more accurate computation. 

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