Pune researchers find massive, grand-design spiral galaxy existing since universe’s infancy

Two researchers from an astrophysics institute in Pune have discovered one of the most distant spiral galaxies ever observed - a massive, well-formed system that existed when the universe was just 1.5 billion years old.

The finding adds to growing evidence that the early universe was more evolved than previously assumed, they said.

Named ‘Alaknanda’ after a Himalayan river, the grand-design spiral galaxy challenges existing theories on how early complex galactic structures formed, the researchers said.

“Finding such a well-formed spiral galaxy at this early epoch is quite unexpected. It shows that sophisticated structures were being built much earlier than we thought possible,” one of the researchers said.

Despite being present when the universe was only 10 per cent of its current age, Alaknanda appears strikingly similar to the Milky Way. The findings have been published in the European journal ‘Astronomy & Astrophysics’.

Using NASA’s James Webb Space Telescope (JWST), researchers Rashi Jain and Yogesh Wadadekar from the Pune-based National Centre for Radio Astrophysics (NCRA-TIFR) identified the galaxy.

“Alaknanda lies at a redshift of about 4, meaning its light has travelled more than 12 billion years to reach Earth,” Jain said.

“We are seeing this galaxy as it appeared just 1.5 billion years after the Big Bang. Finding such a well-formed spiral galaxy at this early epoch is quite unexpected. It shows that sophisticated structures were being built much earlier than we thought possible,” she said.

Using JWST’s infrared sensitivity and resolution, the team found that Alaknanda contains roughly “10 billion times the mass of the sun in stars” and is forming new stars at about 63 solar masses per year, nearly 20 to 30 times the Milky Way’s current rate, the researchers said in a release.

Before JWST, astronomers believed early galaxies were chaotic and clumpy, with stable spiral structures emerging only after several billion years, they said.

Dominant models suggested that early galaxies were too “hot” and turbulent to form ordered disks capable of sustaining spiral arms, the release said.

“Alaknanda tells a different story,” Wadadekar said. “This galaxy had to assemble 10 billion solar masses of stars and build a large disk with spiral arms in just a few hundred million years. That’s incredibly rapid by cosmic standards,” he said.

The discovery adds to growing JWST evidence that the early universe was more evolved than previously assumed.

“While other disk galaxies have been spotted at similar distances, Alaknanda is among the clearest examples of a spiral galaxy with well-defined arms at such a high redshift,” the release said.

Jain said the team chose the name Alaknanda - one of the two main headstreams of the river Ganga - because of its connection to the Milky Way.

“Just as the Alaknanda is the sister river of the Mandakini, which is the Hindi name for our own Milky Way, we thought it fitting to name this distant spiral galaxy after the Alaknanda river,” she said.

Although Alaknanda’s photometric redshift is well-established, follow-up observations with JWST’s NIRSpec instrument or the Atacama Large Millimeter/submillimeter Array (ALMA) are required to measure its disk rotation, the researchers said.

“These measurements will reveal whether the galaxy’s disk is ‘cold’ and orderly or ‘hot’ and turbulent, helping scientists understand how its spiral arms formed,” they added.