Two Indian astronomers have used data from Nasa’s James Webb Space Telescope (JWST) to discover an ancient and massive galaxy with two well-defined spiral arms that appears to challenge standard ideas about the evolution of galaxies.
The JWST image captures the galaxy when the universe was 1.5 billion years old — about a tenth of its current age — and reveals a spiral structure strikingly similar to the Milky Way, the astronomers at the National Centre for Radio Astrophysics in Pune said.
Rashi Jain, a PhD scholar at the NCRA, screened nearly 74,000 galaxies catalogued by a JWST team across a slice of the sky just one-twentieth the angular width of the full moon. She then selected the most distant and brightest 2,700 for detailed scrutiny and discovered the new galaxy among them.
The galaxy, which Jain has named Alaknanda, contains stars that add up to 10 billion times the Sun’s mass. Standard theories about how galaxies emerge and evolve under gravity cannot explain how the two-armed spiral structure could have emerged so early in the universe.
“It is like seeing a 100-storey building built in three days,” Yogesh Wadadekar, an NCRA astronomer who supervised the galaxy search, told The Telegraph. “We would expect to see such a complex textbook structure to emerge after the universe was at least three billion years old.”
The NCRA astronomers have described their findings in the journal Astronomy and Astrophysics.
Before JWST became operational in early 2022, astronomers believed galaxies in the early universe would be chaotic and clumpy. Standard theories predict that early galaxies were hot and turbulent, requiring time to settle down into well-defined architectures such as two spiral arms.
The discovery of Alaknanda adds to mounting evidence from JWST that the early universe was more mature than previously assumed. Early images of JWST had already revealed large and massive galaxies that were hard to explain in the early universe.
“Alaknanda is the most distant disc-shaped galaxy with two well-defined spiral arms,” Jain said.
Further detailed studies might allow scientists to explain the galaxy’s architecture. One possible explanation, Wadadekar said, could be unusually high gas densities within the galaxy that might allow rapid formation of the spiral structure.
Another possibility could be that gravitational tugs from smaller nearby galaxies might have led to the formation of short-lived spiral structures, Wadadekar said. And JWST just happened to take a snapshot at the right time. A hundred million years in the future, it may look different.