A twin of the Milky Way existed in the young cosmos

A twin of the Milky Way in the young cosmos Keystone-SDA

A billion years after the Big Bang, there was already a spiral galaxy that resembles the Milky Way. This is shown by recent observations made by an international research team using the James Webb Space Telescope (JWST).

Until now scientists had assumed that the formation of such spiral galaxies takes several billion years. The discovery therefore calls into question the previous idea of the formation and development of large galaxies, the scientists write in the journal Astronomy & Astrophysics.

It is true that the James Webb space telescope, which went into operation three years ago, has already detected many galaxies that formed 300 to 500 million years after the formation of the cosmos 13.8 billion years ago. However, these are all small, irregularly shaped systems. According to astronomers, these dwarf galaxies develop into larger and larger galaxies over the course of billions of years through collisions and mergers, eventually forming large spiral galaxies such as our Milky Way.

Diameter of around 60,000 light years

The discovery of a fully formed spiral galaxy just one billion years after the Big Bang therefore comes as a surprise to researchers. The system, named Zhulong after a dragon in Chinese mythology, has a diameter of around 60,000 light years and contains over 100 billion stars – figures that are quite comparable to the Milky Way. And very similar to the Milky Way, Zhulong shows a central thickening of older stars, surrounded by a flat disc with spiral arms in which new stars are being formed.

According to Mengyuan Xiao from the University of Geneva, this raises the question of how such a highly developed and structured spiral galaxy could have formed at such an early stage of cosmic evolution. Xiao and her colleagues tracked down the unusual galaxy as part of the so-called Panoramic Survey. This involves scanning random regions of the sky in parallel with other observations from the Webb telescope. In this way, previously unknown objects in the young cosmos can be detected. “This discovery shows the potential of such parallel observations to discover rare celestial objects,” emphasised Christina Williams, chief scientist of the Panoramic Programme.

And such objects pose a challenge to existing theories on the formation and evolution of galaxies. Xiao and her colleagues hope to detect more evolved galaxies in the young cosmos as part of the Panoramic programme. They also want to use the Webb telescope and the large ALMA radio telescope facility in Chile to take a closer look at Zhulong in order to unravel the history of the formation of this galaxy.

Adapted from German by DeepL/ac

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