2024.10.08

Space oddity: Most distant rotating disc galaxy found

This article is a revised version. Please check the original press release by the European South Observatory here.

This image shows the galaxy REBELS-25 as seen by the Atacama Large Millimeter/submillimeter Array (ALMA), overlaid on an infrared image of other stars and galaxies. The infrared image was taken by ESO’s Visible and Infrared Survey Telescope for Astronomy (VISTA). In a recent study, researchers found evidence that REBELS-25 is a strongly rotating disc galaxy existing only 700 million years after the Big Bang. This makes it the most distant and earliest known Milky Way-like galaxy found to date. (Credit: ALMA (ESO/NAOJ/NRAO)/L. Rowland et al./ESO/J. Dunlop et al. Ack.: CASU, CALET)

An international collaborative research team, including Assistant Professor Hanae Inami (Hiroshima University) and researcher Hiddo Algera (NAOJ/Hiroshima University), has discovered the most distant Milky Way-like galaxy yet observed, using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.

Current understanding of the formation and evolution of galaxies predicts that young galaxies in the early Universe gradually grow by repeated violent collisions and mergers, and therefore are smaller and have more complex shapes and motions than modern galaxies. For a galaxy to be as orderly as our own Milky Way, present theories suggest billions of years of evolution must have elapsed. However, the detection of REBELS-25 challenges that timescale.

The researchers observed that the light reaching us from REBELS-25 was emitted when the Universe was just 700 million years old — a mere five percent of its current age (13.8 billion). Despite its young age, REBELS-25 has a rotating disk structure comparable in size to the Milky Way, a fully grown galaxy.

“It is surprising that a galaxy with a rotating disk existed so soon after the birth of the Universe. It’s an exciting discovery that could change our understanding of how galaxies form,” Inami said of the significance of this discovery.

This research was carried out as part of the ALMA large-scale program “REBELS: Reionization Era Bright Emission Line Survey.” The original ALMA observations from the REBELS survey hinted at possible rotation in REBELS-25, but the resolution of the data was not fine enough to be sure. To properly discern the structure and motion of the galaxy, the team performed follow-up observations with ALMA at a higher resolution, which confirmed its record-breaking nature.

“REBELS-25 immediately struck us as a remarkable galaxy among the 40 targets of the REBELS survey, and these follow-up ALMA observations confirm this first impression in a spectacular fashion,” Algera said.

Surprisingly, the data also hinted at more developed features similar to those of the Milky Way, like a central elongated bar, and even spiral arms, although more observations of REBELS-25 will be needed to confirm this.

“Future observations with the powerful James Webb Space Telescope (JWST) will uncover the light from its young stars at a resolution comparable to that of ALMA,” Algera said.

These future observations of REBELS-25, alongside other discoveries of early rotating galaxies, will potentially transform our understanding of early galaxy formation, and the evolution of the Universe as a whole. Inami expected that “more rotating disk galaxies similar to REBELS-25 could be found as we continue exploring the early Universe.” In the near future, we may have even more evidence that early galaxies evolved much faster than we had previously thought.

This research will be published in the Monthly Notices of the Royal Astronomical Society under the title “REBELS-25: Discovery of a Dynamically Cold Disk Galaxy at z=7.31.”

About ALMA

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan and by NINS in cooperation with the Academia Sinica(AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI). ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.