Webb and Hubble sink deep into the dazzling Whirlpool Galaxy — Space photo of the week

Stars form when vast clouds of dust and hydrogen gas collapse, creating a dense core that heats up until it transforms into a nuclear fusion reactor. What happens in the moments after a star emerges from its birth cloud, however, is a mystery.

This image of one of the spiral arms in the Whirlpool Galaxy (Messier 51) gets astronomers closer to solving that mystery — and in doing so, could answer a key question about the early universe.

Made by combining data from the James Webb Space Telescope (JWST) and the Hubble Space Telescope, the image shows that larger groups of stars leave their birth clouds much quicker than smaller ones. It is just one of a series from a paper published May 6 in the journal in Nature Astronomy, which reveals the processes that shape different galaxies.

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As more stars are born in a collapsing cloud, strong stellar winds, harsh ultraviolet light, and powerful explosions called supernovas begin to push the surrounding gas away. This process, called stellar feedback, keeps much of a galaxy's gas from turning into new stars.

In this photo, red-orange threads of gas and dust stretch into lines, while blue bubbles light up some areas from the inside. Gaps in the gas show bright white groups of stars. (JWST's ability to see infrared light uncovered new stars that would be hidden behind dust with normal telescopes.)

When combined with the other images from the study, this showed a clear pattern: the largest groups of stars cleared their birth gas clouds in about 5 million years, while smaller groups took between 7 and 8 million years to fully emerge. That has major implications for how galaxies evolve — and how the universe became hot again about 500 million to 1 billion years after the Big Bang.

After the universe cooled, electrons and protons combined to form neutral atoms. Later, an unknown energy source separated them again during a period called reionization. Could this have been caused by the intense ultraviolet radiation released into galaxies by massive star clusters?

"It had to be the formation of massive star clusters that helped drive the reionization of the universe," study co-author Daniela Calzetti of the University of Massachusetts Amherst, said in a statement. "The fact that the most massive clusters can emerge from their natal clouds in just 5 million years means that they had enough time for producing the photons that reionized the universe."