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The James Webb Space Telescope (JWST) has recently made a groundbreaking discovery, identifying a peculiar "inside-out" galaxy that formed in the universe's early days. The galaxy, designated as JADES-GS+53.18343-27.79097, emerged just 700 million years after the Big Bang. This galaxy is significantly smaller compared to the Milky Way, being approximately 100 times tinier. Unlike typical galaxies, JADES-GS+53.18343-27.79097 appears to have grown from the outside in, with star formation occurring more rapidly on its periphery rather than in its dense core.

The discovery, reported on October 11 in the journal *Nature Astronomy*, is a confirmation of theoretical models that have long suggested such inside-out growth patterns should be prevalent in the early universe. Until now, astronomers lacked the instruments to penetrate the dust and gas that shrouded these galaxies. "One of the many reasons that Webb is so transformational to us as astronomers is that we're now able to observe what had previously been predicted through modeling," remarked William Baker, a study co-author and graduate student at the University of Cambridge. "It's like being able to check your homework."

In contrast to local galaxies that usually expand either by amassing gas to form new stars or by merging with smaller galaxies, the mechanisms of growth in the early universe remain largely unexplored. "The question of how galaxies evolve over cosmic time is an important one in astrophysics," explained Sandro Tacchella, co-lead author and professor of astrophysics at the University of Cambridge. "We've had lots of excellent data for the last 10 million years and for galaxies in our corner of the universe, but now with Webb, we can get observational data from billions of years back in time, probing the first billion years of cosmic history, which opens up all kinds of new questions."

To delve into these mysteries, researchers used data from the JWST's JADES (JWST Advanced Deep Extragalactic Survey) survey. Since light travels at a constant speed through space, JWST's ability to view the most distant light source allows astronomers to peer deep into the past. Analyzing this light using JWST's Near-Infrared Spectrograph (NIRSpec) instrument enabled scientists to determine the ages of the stars within JADES-GS+53.18343-27.79097.

This analysis revealed that the galaxy features a densely packed core surrounded by a disc of gas and dust where stars are forming at an exceptional rate. This rapid formation causes the galaxy to double in size roughly every 10 million years, a stark contrast to the Milky Way's significantly slower doubling rate of 10 billion years. Once formed, these stars migrate inward, accelerating the galaxy's rotation, similar to an ice skater pulling their arms in to spin faster.

The researchers now aim to identify more galaxies like JADES-GS+53.18343-27.79097 to further understand this phenomenon. "Of course, this is only one galaxy, so we need to know what other galaxies at the time were doing," said Tacchella. "Were all galaxies like this one? We're now analyzing similar data from other galaxies. By looking at different galaxies across cosmic time, we may be able to reconstruct the growth cycle and demonstrate how galaxies grow to their eventual size today."