Thanks to the extraordinary sensitivity of the James Webb Space Telescope, scientists have discovered a vast spiral galaxy that formed when the Universe was only 1.5 billion years old. It has been named Alaknanda. Its mystery lies in the fact that it usually takes much longer for such star systems to form.
Alaknanda galaxy. Source: phys.org
Spiral galaxy from the early Universe
A spiral galaxy, very similar in shape to our Milky Way, was discovered at a time when astronomers believed that such well-formed galaxies could not yet exist. Two astronomers from India have discovered an extremely mature galaxy that appeared only 1.5 billion years after the Big Bang — a discovery that challenges our understanding of how galaxies form and evolve.
NASA’s James Webb Space Telescope is a powerful telescope capable of detecting extremely faint light from the early Universe. Using JWST, researchers Rashi Jain and Yogesh Wadadekar discovered a galaxy that is extremely similar to our Milky Way. However, this system formed when the Universe was only 1.5 billion years old — about one-tenth of its current age.
They named it Alaknanda after the Himalayan river, which is the twin of Ganga near Mandakini, which is fitting, since Hindi is the name of the Milky Way.
How was the Alaknanda galaxy formed?
It was believed that classical spiral galaxies, such as ours, with two distinct symmetrical arms (so-called grand design spiral galaxies), form over billions of years. The prevailing opinion was that early galaxies should look irregular and disorderly, still in the chaotic process of formation, rather than in the state of elegant spirals that we so often see in the nearby Universe.
Creating a large spiral takes time: gas has to continuously flow in from the surrounding space (this is called “gas accretion”), settle into a rotating disk, then slow waves (called “density waves”) can disrupt the disk, forming spiral arms, and the whole system has to stay out of the way of violent collisions.
Alaknanda does not meet these expectations. It already has two wide spiral arms enveloping a bright, rounded central region (the bulge of the galaxy) that extends about 30,000 light-years. Even more impressive is that it gives birth to new stars every year, with a total mass of about 60 times that of the Sun.
This figure is approximately 20 times higher than that of the modern Milky Way! Approximately half of the stars in Alaknanda seem to have formed in just 200 million years — a mere instant in cosmic time.
The discovery of such a well-organized spiral disk in this era indicates that the physical processes responsible for galaxy formation—gas accretion, disk settling, and possibly the development of spiral density waves—may be much more effective than modern models suggest. This forces us to rethink our theoretical framework.
Gravitational lensing
Alaknanda is located in the direction of a huge galaxy cluster called Abell 2744, also known as the Pandora Cluster. The cluster’s immense gravity bends and magnifies light from distant cosmic objects in its background, much like a magnifying glass. This effect, called gravitational lensing, made Alaknanda appear twice as bright, allowing JWST to capture its spiral structure in stunning detail.
Jain and Wadadekar analyzed images of the galaxy taken by JWST using 21 different filters, each showing a different part of its light. This rich array of data, part of the JWST UNCOVER and MegaScience studies, allowed them to estimate the distance to the galaxy, its dust content, the number of stars in the galaxy, and the rate of new star formation over time with extraordinary precision.
Correspondence of space chronology
This discovery adds to the growing body of evidence from JWST that the early Universe was much more mature than astronomers had expected. Several disk-shaped galaxies have been discovered at such vast distances, but Alaknanda stands out as one of the most striking examples of a “grand design” spiral (a galaxy with two distinct symmetrical arms) at such an early epoch.
Now scientists will discuss how Alakanda’s spiral arms came into being. One possibility is that the galaxy grew steadily, drawing in streams of cold gas, which allowed density waves to naturally carve out spiral patterns. Another possibility is that a gravitational collision with a smaller companion galaxy triggered the formation of the arms, although such tidally-induced spirals usually disappear quickly.
Future observations using JWST spectroscopic instruments or the Atacama Large Millimeter Array (ALMA) telescope in Chile will allow us to measure the galaxy’s rotation speed and determine whether its disk is moving in an orderly (dynamically cold) or more turbulent (dynamically hot) manner, which will help distinguish between these scenarios.
Importance of discovery
This discovery is not just a pretty picture from the distant past. It forces astronomers to rethink cosmic chronology—the history of the formation of stars, galaxies, and, finally, planets such as Earth. If galaxies could mature so quickly, then the early Universe was a much more dynamic and fertile place than we imagined, and the conditions for the formation of worlds like ours could have arisen earlier than anyone could have imagined.
As JWST continues to peer deeper into space and time, more galaxies like Alaknanda will appear—each offering new clues about the surprisingly rapid early evolution of the Universe.
According to phys.org