In a groundbreaking discovery, the James Webb Space Telescope (JWST) has peered into the distant past, revealing a strange and intriguing galaxy that challenges our current understanding of how galaxies evolve. This galaxy, named JADES-GS+53.18343−27.79097, existed a mere 700 million years after the Big Bang, a time when the universe was still in its infancy.
What makes this galaxy truly remarkable is its unconventional growth pattern. Unlike most galaxies, which tend to grow outwards from their core, this one seems to be developing in reverse, with stars forming more rapidly on its outskirts than in its dense central region. This phenomenon, known as ‘inside-out’ growth, has long been predicted by theoretical models, but until now, astronomers lacked the necessary tools to observe these elusive galaxies, shrouded in dust and gas.
Thanks to the exceptional capabilities of JWST, researchers have finally been able to penetrate these barriers, confirming the existence of these predicted ‘inside-out’ galaxies and glimpsing the earliest one ever seen. The discovery, published in the journal Nature Astronomy, sheds new light on the intricate processes that govern the formation and evolution of galaxies in the early universe.
“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,” explains William Baker, a graduate student at the University of Cambridge and co-author of the study. “It’s like being able to check your homework.”
The study of galaxies in our local universe suggests that they grow through two primary mechanisms: capturing enough gas to form new stars or merging with smaller galaxies. However, the question remains: are these the only mechanisms at play, or did other processes contribute to galaxy growth in the earlier stages of the universe?
“The question of how galaxies evolve over cosmic time is an important one in astrophysics,” says Sandro Tacchella, professor of astrophysics at the University of Cambridge and co-lead author of the study. “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 investigate this question, the researchers delved into data collected during JWST’s JADES (JWST Advanced Deep Extragalactic Survey) survey, focusing on ancient galaxies. Since light travels at a finite speed through the vacuum of space, the deeper JWST observes into the universe, the further back in time it can effectively see. It was through these observations that this peculiar galaxy was revealed.
By analyzing the light emanating from the stars within the galaxy using JWST’s Near-Infrared Spectrograph (NIRSpec) instrument, the researchers were able to determine the ages of the stars. The analysis revealed a galaxy with a dense core surrounded by a disc of gas and dust, where stars are forming rapidly. This rapid star formation is causing the galaxy to double in size every 10 million years, a rate far exceeding the Milky Way’s doubling rate of 10 billion years.
As these stars mature, they gradually migrate towards the core, causing the galaxy to spin faster, akin to an ice skater pulling their arms in closer to their body. This discovery opens a new window into the mechanisms that shape the evolution of galaxies, offering valuable insights into the intricate processes that have shaped the universe we know today.
The researchers are now eager to search for more galaxies similar to this remarkable discovery. “Of course, this is only one galaxy, so we need to know what other galaxies at the time were doing,” says 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.”
The James Webb Space Telescope continues to unravel the mysteries of the universe, pushing the boundaries of our understanding of the cosmos and providing us with a glimpse into the fascinating past of galaxies, like this ‘inside-out’ galaxy, that are reshaping our understanding of cosmic evolution.