A galaxy has been discovered in a place where it shouldn't exist, baffling astronomers with its location and age. This galaxy, strikingly similar to our Milky Way, challenges current understandings of the early universe.
Around a billion years after the Big Bang, the universe began to settle into its more stable state, and it hasn’t changed much since. Before this period, however, things were far more chaotic—at least, that’s what scientists believed.
Galaxies are a prime example of this assumption.
Roughly 50-80% of galaxies within 7 billion light-years of Earth are organized, with a characteristic rotating disc shape, like the Milky Way. In the universe's early years, such orderly structures weren’t expected to exist.
Yet, new observations, detailed in a paper published in the Monthly Notices of the Royal Astronomical Society, reveal the surprising existence of such a galaxy.
A Surprising Discovery
Named REBELS-25, it appears at a redshift of z=7.31, meaning it dates back to a time when the universe was only 700 million years old. The oldest known galaxies are just a few hundred million years older.
True to its name, REBELS-25 defies expectations.
Astronomers have found evidence of an ordered structure and rotation within this galaxy, and it may even feature a central bar and spiral arms. These characteristics are unusual for galaxies of its age, which are generally smaller, chaotic, and disordered.
“As far as we know about galaxy formation, we would expect most early galaxies to be small and disorganized,” explains Jacqueline Hodge, an astronomer at Leiden University and a co-author of the study.
Current theories suggest that structures like rotating discs and spiral arms, typical of galaxies like the Milky Way, should take billions of years to form.
“Discovering a galaxy with such similarities to our Milky Way, dominated by rotation, challenges our understanding of how quickly galaxies evolve in the early Universe,” says Lucie Rowland, the study's lead author and a doctoral student at Leiden University.
The discovery was made possible by the Atacama Large Millimeter/submillimeter Array (ALMA), a facility in which the European Southern Observatory (ESO) is a key partner.
“ALMA is the only telescope with the sensitivity and resolution to uncover such details,” adds Renske Smit, a researcher at Liverpool John Moores University and co-author of the study.
