In a groundbreaking discovery, astronomers have spotted the most distant rotating galaxy ever observed, which could upend existing theories of galactic evolution. This galaxy, designated REBELS-25, was discovered just 700 million years after the Big Bang, placing it in the very early stages of cosmic history. Yet, against all expectations, it shows signs of rapid development, with characteristics more akin to mature galaxies like our Milky Way.
A Discovery That Defies Expectations
REBELS-25 was detected by a team of international astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA), a network of 66 radio telescopes in Chile’s Atacama Desert. What makes this galaxy truly remarkable is that it appears far more organized than expected for such an early time in the universe’s life. In contrast to the chaotic and clumpy appearance typical of other early galaxies, REBELS-25 shows signs of being a well-structured, rotating disk galaxy, hinting at spiral arms—an astonishing level of order for a galaxy that existed when the universe was only 5% of its current age.
Team member Jacqueline Hodge, an astronomer at Leiden University in the Netherlands, expressed her astonishment at the discovery: “According to our understanding of galaxy formation, we expect most early galaxies to be small and messy-looking.” However, REBELS-25 has defied this assumption, appearing as a galaxy more advanced than its peers from that era.
REBELS-25: A Tidy Rebel in a Chaotic Early Universe
Modern galaxies like the Milky Way have had billions of years to develop into their distinctive shapes. Their spiral arms, rotating disks, and central bars are the result of slow and steady evolution through cosmic collisions and mergers. In contrast, early galaxies—such as those formed just after the Big Bang—are expected to be clumps of gas and dust, slowly evolving over time.
However, REBELS-25 disrupts this expected timeline. It is not only spinning in an organized manner but may also have features resembling those of the Milky Way, such as spiral arms and a central bar of stars. These elements usually take billions of years to develop, yet REBELS-25 already shows signs of such complexity.
Lucie Rowland, the study’s lead researcher, also of Leiden University, highlighted the significance of this discovery: “Seeing a galaxy with such similarities to our own Milky Way, that is strongly rotation-dominated, challenges our understanding of how quickly galaxies in the early universe evolve into the orderly galaxies of today’s cosmos.”
The Science Behind the Spin
To confirm their findings, the team behind REBELS-25 turned to the powerful capabilities of ALMA. Initial observations hinted at rotation, but the resolution was too low to definitively determine the galaxy’s motion. The team then used a higher resolution to track the movement of cold gas within the galaxy, detecting shifts in the light spectrum that confirmed it was indeed rotating.
This was done through a process known as redshift and blueshift. When light moves towards an observer, its wavelength shortens, making it appear blue. Conversely, when light moves away, it stretches into the red spectrum. By tracking these shifts, the astronomers could map the rotation of the galaxy—showing that parts of REBELS-25 were moving both towards and away from Earth, confirming its disk-like structure.
“ALMA is the only telescope in existence with the sensitivity and resolution to achieve this,” explained Renske Smit, a team member from Liverpool John Moores University in the UK.
Spirals in the Early Universe?
The discovery of REBELS-25 could lead to yet another significant milestone. Hints suggest that the galaxy may have developed spiral arms, a feature typically seen in mature galaxies billions of years old. If confirmed, REBELS-25 would be the earliest spiral galaxy ever observed, surpassing the current record held by a galaxy called CHEERS-2112, which was discovered by the James Webb Space Telescope (JWST) when the universe was around 2.1 billion years old.
“Finding further evidence of more evolved structures would be an exciting discovery, as it would be the most distant galaxy with such structures observed to date,” Rowland added.
What This Means for Galactic Evolution
The discovery of REBELS-25 has significant implications for our understanding of how galaxies form and evolve. Theories have long suggested that galaxies in the early universe should be disorganized, gradually evolving over billions of years into the well-defined galaxies we see today. However, the existence of REBELS-25 so early in cosmic history suggests that galaxy formation may have happened much faster and more efficiently than previously believed.
Further research is needed to determine just how common galaxies like REBELS-25 were in the early universe and whether they are an exception or part of a broader trend of early galactic development.
Conclusion
The discovery of REBELS-25 opens new questions about the timeline of galaxy evolution, with this distant galaxy offering a glimpse into a universe that seems far more advanced than it should be. As astronomers continue to explore the mysteries of the early cosmos, this rebellious galaxy serves as a reminder that even our best theories are subject to revision in the face of new evidence.
