Updated on: December 04, 2025 | By: Jameswebb Discovery Editorial Team

Why Alaknanda Challenges Early Universe Theories

Indian astronomers Rashi Jain and Prof. Yogesh Wadadekar from the National Centre for Radio Astrophysics (NCRA-TIFR) in Pune have made a stunning breakthrough. Using data from the James Webb Space Telescope (JWST), they identified Alaknanda, a massive grand-design spiral galaxy that existed just 1.5 billion years after the Big Bang – when the Universe was only about 10% of its current age. Seen as it was 12 billion years ago at a photometric redshift of z ≈ 4.05, Alaknanda features a well-organized rotating disk, two prominent symmetric spiral arms, a bright central bulge, and the classic "beads-on-a-string" pattern of young star clusters along its arms – making it a remarkable twin to our own Milky Way.

Why Alaknanda Challenges Early Universe Theories

For decades, astronomers believed high-redshift galaxies (z > 3) were mostly chaotic, clumpy, and irregular due to turbulent conditions in the young Universe. Stable spiral structures were thought to require billions of years of calm evolution.Alaknanda defies this:

• Redshift: z ≈ 4.05 (Universe age ~1.5 billion years)

• Physical diameter: 10 kpc (30,000–40,000 light-years)

• Stellar mass: log(M⋆/M⊙) ≈ 10.2 (~16 billion solar masses)

• Star formation rate (SFR): ~63 M⊙/year (20–30 times higher than the modern Milky Way)

• Specific SFR: log(sSFR) ≈ -8.37 yr⁻¹

• Mass-weighted age: ~199 million years

• Dust extinction: A_V ≈ 0.9 (moderately dusty)

• Morphology: Two-armed grand-design spiral with low bulge-to-total ratio (B/T ≈ 0.14–0.18), overwhelmingly disk-dominated

This rapid assembly – building a massive, ordered spiral in just a few hundred million years – suggests the early Universe was far more efficient at forming sophisticated structures than predicted.

How Indian Astronomers Discovered Alaknanda

Jain spotted Alaknanda while visually inspecting over 70,000 objects in JWST's UNCOVER (Ultradeep NIRSpec and NIRCam Observations before the Epoch of Reionization) survey of the Abell 2744 (Pandora’s Cluster) field, combined with the Medium Band MegaScience survey.The massive foreground cluster provided gravitational lensing magnification (~2.3×), boosting brightness and enabling JWST's NIRCam to resolve details across 21 filters (broadband + medium-band).Detailed analysis included:

• SED modeling with BAGPIPES (delayed/exponential SFH) and comparison to Prospector

• Parametric fitting with GALFIT (bulge + disk decomposition)

• Non-parametric morphology (CASGM parameters: concentration, asymmetry, Gini, M20) – placing Alaknanda firmly in the "disk galaxy" region

Emission-line maps (continuum-subtracted F250M and F335M filters) show star formation concentrated along the arms, with H-α and [OIII] tracing active regions.The name Alaknanda honors one of the Himalayan headstreams of the Ganga, sister to the Mandakini (Hindi for Milky Way) – a poetic reflection of its twin-like structure. A nearby spheroid (possible satellite at z ≈ 3.97) hints at tidal interactions influencing the arms.

Broader Context: JWST Rewriting High-Redshift Spiral History

Pre-JWST (Hubble era): Only ~2 spirals known at z > 2; fraction dropped sharply with redshift. With JWST:

• Growing population of disks at z > 3 (e.g., Kartaltepe et al. 2023; Ferreira et al. 2022)

• Individual spirals at z ≈ 3 (Wu et al. 2022; Costantin et al. 2023; Wang et al. 2025)

• Observed spiral fraction ~4–8% at z ~3, but intrinsic ~25% after correcting biases (Kuhn et al. 2024)

Alaknanda is among the most distant and clearest grand-design examples, supporting theories of rapid cold disk settling via smooth gas accretion rather than mergers.Possible arm formation mechanisms:

• Dissolution of clumps in unstable disks

• Tidal perturbations from the candidate satellite

• Density waves in cold disks (less likely bar-driven, as no large bar detected)

Future Observations and Open Questions

Follow-up with JWST NIRSpec/IFU or ALMA could measure kinematics (hot vs. cold disk), gas dynamics, and confirm arm origins. Key questions:

• How did such a large disk form so quickly?

• Are grand-design arms long-lived or transient at high redshift?

• Does this indicate parallel formation pathways in the early Universe?

Stay Ahead with Every James Webb Discovery

JamesWebbDiscovery.com delivers detailed, timely coverage of JWST breakthroughs – from early Universe surprises to exoplanet insights. Recent Highlight:

• Closest Dwarf Galaxy Dance: NGC 4490 & NGC 4485 Tidal Bridge

JWST proves the early Universe was far more mature and creative than imagined – with Indian astronomers at the forefront.

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