Pioneering Discovery: India's Astrophysicists Unveil 'Alaknanda' Galaxy

Pune, Dec 3 (PTI) — In a groundbreaking discovery, two researchers from Pune's astrophysics institute have identified one of the universe's most distant spiral galaxies, which was formed when the cosmos was just 1.5 billion years old. This finding contributes to the expanding body of evidence suggesting that the early universe was more evolved than previously believed.

The galaxy has been christened 'Alaknanda', after the Himalayan river, and its discovery is posing challenges to current theories concerning the formation of early complex galactic structures. "Discovering such a well-formed spiral galaxy at this early stage is highly unexpected. It reveals that intricate structures were being established much earlier than we had thought possible," said one of the researchers.

Despite existing when the universe was only 10% of its present age, Alaknanda bears a striking resemblance to our Milky Way. The study has been published in the prestigious journal 'Astronomy & Astrophysics'.

Using NASA's James Webb Space Telescope (JWST), Rashi Jain and Yogesh Wadadekar from the National Centre for Radio Astrophysics (NCRA-TIFR) in Pune discovered the galaxy. "Alaknanda is located at a redshift of approximately 4, indicating that its light has traveled over 12 billion years to reach Earth," Jain mentioned.

She elaborated, "We are observing this galaxy as it appeared merely 1.5 billion years after the Big Bang. Finding such a well-formed spiral galaxy this early on is quite unexpected. It suggests that sophisticated structures were emerging much sooner than previously thought."

Thanks to JWST's infrared sensitivity and resolution, the team determined that Alaknanda possesses around "10 billion times the mass of the sun in stars" and is producing new stars at a rate of approximately 63 solar masses per year, which is nearly 20 to 30 times the current rate of the Milky Way, according to the researchers.

Before the advent of JWST, astronomers had presumed that early galaxies were chaotic and clumpy, with stable spiral structures developing only after several billion years. Dominant models had suggested that early galaxies were too "hot" and turbulent to form ordered disks capable of sustaining spiral arms.

"Alaknanda presents a different narrative," said Wadadekar. "This galaxy had to accumulate 10 billion solar masses of stars and create a vast disk with spiral arms in just a few hundred million years. That is incredibly rapid by cosmic standards," he noted.

The discovery supports accumulating JWST evidence that the early universe was more developed than previously assumed. "Even though other disk galaxies have been observed at similar distances, Alaknanda stands out as one of the clearest examples of a spiral galaxy with well-defined arms at such a high redshift," the researchers shared.

Jain explained that the team chose the name Alaknanda for its connection to the Milky Way. "Just as the Alaknanda is the sister river to the Mandakini, which is the Hindi name for our Milky Way, we felt it appropriate to name this distant spiral galaxy after the Alaknanda river," she said.

Although Alaknanda's photometric redshift is well-determined, follow-up observations using JWST's NIRSpec instrument or the Atacama Large Millimeter/submillimeter Array (ALMA) are required to measure its disk rotation, the researchers emphasized. "These observations will unveil whether the galaxy's disk is 'cold' and orderly or 'hot' and turbulent, aiding scientists in understanding the formation of its spiral arms," they concluded.