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Breakthrough Discovery of Distant Milky-Way-Like Galaxy REBELS-25

Astronomers have made a groundbreaking discovery with the identification of REBELS-25, the furthest Milky-Way-like galaxy observed to date. This disc galaxy appears strikingly organized, resembling modern galaxies, yet it is being viewed as it was just 700 million years after the Big Bang. This finding is surprising as current models of galaxy formation suggest that such early cosmic structures would be more chaotic and less structured. The Atacama Large Millimeter/submillimeter Array (ALMA), in collaboration with the European Southern Observatory (ESO), played a key role in revealing the intricate rotation and architecture of REBELS-25.

Today’s galaxies have significantly evolved from their earlier, irregular forms, which astronomers often associate with the nascent Universe. “Most early galaxies are expected to be smaller and exhibit a messy appearance,” notes Jacqueline Hodge, an astronomer from Leiden University in the Netherlands and a co-author on the study.

These primordial galaxies typically merge over time, gradually achieving more uniform shapes. The prevailing theories suggest that a galaxy must undergo billions of years of transformative evolution to develop an aligned structure akin to our Milky Way, which features neatly formed spiral arms. However, the discovery of REBELS-25 poses a challenge to this timeline.

The findings from the study, which has been accepted for publication in Monthly Notices of the Royal Astronomical Society, indicate that REBELS-25 represents the most distant galaxy characterized by substantial rotation speed. The light we observe from this galaxy today has been on its journey for 700 million years, equivalent to a mere five percent of the Universe’s current age, estimated at 13.8 billion years. “Observing a galaxy that closely resembles our Milky Way, particularly one that displays such strong rotational characteristics, raises important questions about the speed at which early galaxies transform into the more structured galaxies we see now,” comments Lucie Rowland, a doctoral candidate at Leiden University and primary author of the study.

Initially detected in prior studies by the same research team using ALMA, REBELS-25 showed early signs of rotation but lacked sufficient resolution for a conclusive analysis. To gain clearer insights into the galaxy’s structure and dynamics, the team conducted follow-up observations with a heightened resolution at ALMA, ultimately affirming its unprecedented status. “ALMA stands alone in its ability to provide both the sensitivity and resolution necessary for this work,” states Renske Smit, a researcher at Liverpool John Moores University in the UK and a co-author of the study.

Interestingly, the data collected hints at more complex features within REBELS-25 that resemble those of the Milky Way, such as a central elongated bar and potential spiral arms, though additional observations will be necessary to substantiate these claims. “Discovery of more advanced structures in such a distant galaxy would be groundbreaking, potentially marking it as the farthest galaxy known to exhibit such features,” adds Rowland.

The ongoing and future investigations into REBELS-25, supplemented by the discoveries of additional early rotating galaxies, may significantly enhance our understanding of the processes involved in the formation of galaxies and the expansive evolution of the Universe itself.

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