Researchers have found the farthest galaxy that resembles the Milky Way ever detected. Known as REBELS-25, this disc galaxy appears as orderly as modern galaxies, yet we observe it from a time when the Universe was just 700 million years old. This is surprising because our current knowledge of galaxy formation suggests that galaxies this early should look much more chaotic.
Researchers have found the farthest galaxy that resembles the Milky Way ever detected. Known as REBELS-25, this disc galaxy appears as orderly as modern galaxies, yet we observe it from a time when the Universe was just 700 million years old. This is surprising because our current knowledge of galaxy formation suggests that galaxies this early should look much more chaotic. The characteristics of REBELS-25, including its rotation and structure, were unveiled using the Atacama Large Millimeter/submillimeter Array (ALMA), a project supported by the European Southern Observatory (ESO).
The galaxies we observe today have transformed from their chaotic, uneven counterparts typically seen in the early Universe. “Based on our understanding of galaxy formation, we expect that most early galaxies would be small and disordered,” explains Jacqueline Hodge, an astronomer from Leiden University in the Netherlands, and a co-author of this study.
These disordered early galaxies collide and gradually evolve into more organized shapes over an extremely extended period. Current theories indicate that for a galaxy to resemble our own Milky Way — characterized by a rotating disc and well-defined features like spiral arms — billions of years would need to pass. However, the discovery of REBELS-25 questions this evolutionary timeline.
In a study awaiting publication in the *Monthly Notices of the Royal Astronomical Society*, researchers identified REBELS-25 as the most distant galaxy with a strong rotational disc ever found. The light we see from this galaxy was emitted when the Universe was merely 700 million years old — just five percent of its current age (13.8 billion years) — which makes its organized rotation quite unexpected. “Witnessing a galaxy that shares features with our own Milky Way, and that is dominantly rotating, challenges our perception of how quickly early galaxies develop into the structured galaxies we observe today,” comments Lucie Rowland, a PhD student at Leiden University and the lead author of the study.
REBELS-25 was first identified in earlier observations from the same team, which were also conducted using ALMA in Chile’s Atacama Desert. This initial discovery was thrilling as it indicated some rotation, but the data lacked the precision needed for confirmation. To accurately analyze the galaxy’s structure and movement, the team conducted follow-up observations with ALMA at a higher resolution, verifying its groundbreaking status. “ALMA is currently the only telescope capable of providing the sensitivity and resolution required to achieve this,” states Renske Smit, a researcher at Liverpool John Moores University in the UK and another co-author of the study.
Interestingly, the data also suggested more complex features akin to those seen in the Milky Way, such as a central elongated bar and even spiral arms, though more research is necessary to validate these findings. “Finding additional proof of these sophisticated structures would be an exciting milestone, marking the most distant galaxy with such features to date,” remarks Rowland.
Future studies of REBELS-25, along with other discoveries of early rotating galaxies, may revolutionize our comprehension of early galaxy formation and the broader evolution of the Universe.
