This galaxy named Alaknanda is changing astronomers’ thinking about how such objects are formed.
This image, captured by the James Webb Space Telescope, shows Alaknanda (inset), located within the boundaries of the Sculptor constellation behind a galaxy cluster called Abell 2744.
Credit: NASA/ESA/CSA, I. Labbe/R. Bezanson/Alyssa Pagan (STSCI), Rashi Jain/Yogesh Vadadekar (NCRA-TIFR)
- A grandiose-designed spiral galaxy named Alaknanda was discovered about 1.5 billion years after the Big Bang, challenging previous astrophysical models on the timescale required for galaxies to achieve such structural maturity.
- The researchers used NASA’s James Webb Space Telescope (JWST) and the natural magnifying effect of gravitational lensing by the galaxy cluster Abell 2744 to observe Alaknanda’s detailed spiral structure.
- Alaknanda exhibits features such as two broad spiral arms, a bright central region 30,000 light years wide, and a star formation rate 20 times faster than the Milky Way, which were unexpected for a galaxy of its cosmic age.
- This discovery requires a reassessment of current theoretical frameworks for galaxy formation, suggesting that processes such as gas accretion, disk settlement, and the evolution of spiral density waves may have operated far more efficiently in the early universe than previously predicted.
A paper, published in astronomy and astrophysicsDetails the discovery of a grandiosely-designed spiral galaxy that formed just 1.5 billion years after the Big Bang. Galaxies with grand designs resemble the Milky Way in that they exhibit well-formed spiral arms. Before this discovery, astronomers thought that such objects took billions of years to achieve grand-design status. apparently not.
Using NASA’s James Webb Space Telescope (JWST), researchers Rashi Jain and Yogesh Wadekar, working at the National Center for Radio Astrophysics at the Tata Institute of Fundamental Research in India, observed a galaxy that was remarkably similar to our own Galaxy, but which apparently formed when the universe was 1.5 billion years old. they named it AlaknandaFollowing the Himalayan River which is a twin headstream Ganges together with Mandakini, which is Hindi name of galaxy.
Both astronomers studied JWST images Alaknanda Taken through 21 different filters. This data allowed them to estimate the galaxy’s distance, the amount of dust, how many stars it contains, and how fast new stars are forming over time.
They were able to analyze it because Alaknanda lies behind the giant galaxy cluster Abell 2744. The combined gravity of the group members bent and enhanced the young galaxy’s light. This effect, known as gravitational lensing, made Alaknanda twice as bright, allowing JWST to capture its spiral structure in stunning detail.
a galactic exception
Until this discovery, astronomers thought that galaxies that formed so early should appear irregular and disorganized, essentially still forming. And for one of them to turn into a grand spiral it would take a lot of time for gas to flow in from the surrounding space, settle into a rotating disk and be molded into spiral arms by waves inside the galaxy.
But young Alaknanda already has two broad arms that wrap around a bright, round central region of about 30,000 light years. This galaxy is creating stars 20 times faster than our galaxy. In fact, half of Alaknanda’s stars appear to have formed in just 200 million years.
“Alaknanda has the structural maturity that we associate with galaxies billions of years old,” said Jain, lead author of the study. “The discovery of such well-organized spiral disks at this age tells us that the physical processes driving galaxy formation – gas accretion, disk settlement, and possibly the evolution of spiral density waves – may work far more efficiently than current models predict. It is forcing us to rethink our theoretical framework.”
How did Alaknanda’s spiral arms form so quickly?
This question is the main question that astronomers will try to answer. One theory is that the galaxy grew steadily by stretching out streams of cold gas, allowing density waves to naturally form spiral patterns. The second is that a gravitational encounter with a smaller companion galaxy activated the arms. Future observations with JWST can measure how fast the galaxy is rotating and whether its disk is rotating in an orderly manner or is more turbulent. That data would lend credibility to one of the theories.
“Alaknanda shows that the early universe was capable of galaxy fusion much faster than we expected,” says study co-author Yogesh Vadadekar. “Somehow, this galaxy managed to pull together ten billion solar-mass stars in just a few hundred million years and arrange them into a beautiful spiral disk. This is exceptionally fast by cosmic standards, and it forces astronomers to rethink how galaxies form.”
