Milky Way’s first twin discovered – Oldest known barred spiral contradicts common models of galaxy evolution

November 14, 2023, reading time: 4 minutes.

Contradiction with theory: Astronomers have discovered a surprisingly early twin of the Milky Way: a barred spiral galaxy that is more than 11.7 billion years old. The galaxy named ceers-2112 is not only the oldest barred spiral known, but it also existed much earlier than current models of galaxy evolution predicted. Furthermore, this primordial galaxy is almost exactly the shape and size that our Milky Way must once have been, as the team reports in Nature.

Our Milky Way is one of the barred spirals: at its center runs a straight structure with a greater density of stars, to which the spiral arms attach. This bar constitutes an important material transport pathway and promotes star formation in the inner region of the galaxy. However, it is still unclear why only some spiral galaxies have such a bar and when it manifests itself in the evolution of galaxies. According to current models, such barred spirals have only existed for a few billion years because only then did galaxies have the necessary order and calm.

Our Milky Way is a barred galaxy: its spiral arms extend from the end of a rectilinear structure of stars and dense gas. © NASA/JPL-Caltech/ESO/R. Bad

“It was thought that such bars could not form in early galaxies or at least did not last long because they were still too chaotic and turbulent,” explains co-author Alexander de la Vega of the University of California at Riverside. But in March 2023, new images from the James Webb Space Telescope raised the first doubts about this. In them, astronomers discovered several barred spirals more than ten billion light-years away.

The most distant bar spiral so far

Now there is another discovery, even older: Luca Costantin’s team from the Astrobiological Center of Madrid has discovered another barred spiral galaxy in the near-infrared images of the James Webb telescope. The galaxy called ceers-2112 has a higher redshift at z=3 and therefore existed about two billion years after the Big Bang. However, deeper analyzes of its structure and light spectrum suggest that at that time this galaxy was already 620 million years old.

Contrary to what was initially thought, this galaxy, despite its early formation, already has a clearly pronounced bar, as astronomers have discovered. This is 10,700 light years long and stands out from the rest of the galaxy for its greater density of stars and greater luminosity. “Finding a bar in ceers-2112 is surprising because galaxies were much more chaotic in the early universe,” says de la Vega.

Density contours of the ceers-2112 galaxy (a) determined from images and spectral analyzes (b) show a bar structure at the center of the galaxy. © Constantin et al./Nature, CC-by 4.0

One of the first twins of our home galaxy

But the primordial galaxy Ceres-2112 is not only very similar to our Milky Way in shape. Its other structure and its stellar mass of about 3.9 billion solar masses also make it one of the early twins of our home galaxy: “If we compare ceers-2112 with the history of the development of the Milky Way, then we can consider it the planet most distant and the earliest predecessor of the Milky Way, both in terms of structure and growth,” say Constantin and his colleagues.

“The discovery of ceers-2112 demonstrates that galaxies in the early universe could also be ordered like the Milky Way,” says de la Vega. As astronomers have established, the stellar disk of this early twin of the Milky Way may have formed one to one and a half billion years after the Big Bang. The formation of the ceers-2112 beam began about 200 million years later and was completed within about 400 million years.

“Theories need to be revised”

According to astronomers, this discovery sheds new light on the evolution of galaxies at the dawn of the cosmos. “The bar in ceers-2112 suggests that galaxies have matured and organized more rapidly than we previously thought,” says de la Vega. Until now, it was assumed that this process would only end after several billion years, i.e. around half of our universe. Only then did the strong flows of gas, which enabled the rapid formation of stars in the early cosmos but also caused galactic turbulence, subside.

“But the discovery of this galaxy shows that this can happen in a fraction of that time, in about a billion years or less,” the researcher said. “Our theories on the formation and evolution of galaxies must therefore be revised in at least some aspects.” As a result, the first turbulent phase of star formation may have occurred much faster than previously thought, at least in some galaxies. (Nature, 2023; doi: 10.1038/s41586-023-06636-x)

Source: University of California-Riverside

November 14, 2023 – Nadja Podbregar

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