🔭 A surprising twin of the Milky Way discovered in the baby Universe

How can a galaxy display perfectly defined spiral arms when the Universe had only a little over 10% of its current age? This surprising discovery challenges established models about the birth and evolution of galaxies.

Named Alaknanda, this distant galaxy was spotted by the James Webb Space Telescope. It bears a striking resemblance to the Milky Way, with its two symmetrical spiral arms and a bright central core. Its discovery, made by an Indian team, was published in the journal Astronomy & Astrophysics. Astronomers were astonished by its structural maturity at a time when galaxies were thought to still be chaotic, barely 1.5 billion years after the Big Bang.


The observation was facilitated by a gravitational lensing effect (see below) from the galaxy cluster Abell 2744. This cluster, acting as a cosmic magnifying glass, amplified Alaknanda's light, allowing the JWST to capture unusual details. The researchers used up to 21 different filters to analyze its composition, distance, and star formation history. This technique revealed exceptional clarity for such an ancient object.

Alaknanda produces stars at an impressive rate, equivalent to sixty times the mass of the Sun each year. This rate is about twenty times higher than that of the Milky Way today. Such activity indicates that the young Universe was much more productive than imagined. Half of this galaxy's stars are estimated to have formed in only two hundred million years, a very short interval on the cosmic scale.

This discovery calls into question theories of galaxy formation. It was believed that orderly structures like spirals required billions of years to develop, through slow processes of gas accretion and density waves. Alaknanda shows that these mechanisms could have operated much faster. Astronomers indicate that this forces a revision of existing theoretical frameworks.


To understand the origin of Alaknanda's spiral arms, further investigations are planned. Spectroscopic observations with the JWST or the ALMA array could determine whether its disk rotates in an orderly manner or shows signs of turbulence. This would help identify whether the spiral was born from regular gas inflows or an interaction with a neighboring galaxy (more details on spiral arm formation at the end of the article).

The presence of Alaknanda in the primordial Universe indicates that conditions for planet and star formation could have appeared earlier than expected. As the JWST continues to explore the cosmos, other similar galaxies might be discovered, enriching our understanding of cosmic evolution and the rapidity with which the first organized structures assembled.

The phenomenon of gravitational lensing

Gravitational lensing is an effect where the light from a distant object is bent by the gravity of an intervening mass, such as a galaxy cluster. This effect acts as a natural magnifying glass, amplifying and distorting the image of the background object. In astronomy, this allows observation of very distant galaxies that would otherwise be too faint to detect.

The use of gravitational lensing has transformed the study of the early Universe. By focusing light, it offers details inaccessible with standard telescopes. For example, in the case of Alaknanda, the Abell 2744 cluster doubled the apparent brightness of the galaxy, allowing the JWST to capture its fine structure.

This tool is also crucial for measuring parameters such as the distance and mass of cosmic objects. By analyzing how light is deflected, scientists can map the distribution of dark matter in the Universe.

The formation of spiral arms in galaxies

The spiral arms of galaxies, like those of the Milky Way, form thanks to density waves that travel through the galactic disk. These waves are disturbances in the distribution of gas and stars, creating regions where matter concentrates and triggers star formation. This process gives rise to the characteristic patterns we observe.

For a spiral to develop, gas must first accrete from the external environment and stabilize into a rotating disk. Then, gravitational interactions, either internal or with companion galaxies, can initiate the density waves. These gradually sculpt the disk into spiral arms, an arrangement that typically requires billions of years to reach a stable form.

In the case of ancient galaxies like Alaknanda, the presence of well-defined spiral arms indicates that these mechanisms could have operated with surprising efficiency. This implies that the young Universe had favorable conditions, such as regular inflows of cold gas, allowing accelerated evolution. Understanding these processes helps explain how galaxies could achieve structural maturity so quickly.