James Webb Space Telescope reveals early galaxies do not follow star-heavy element relation

The launch of the James Webb Space Telescope marks a significant milestone in astronomy, enabling us to glimpse back in time toward the era when the first galaxies emerged. For much of cosmic history, galaxies have seemed to adhere to a consistent pattern: the more stars they birthed, the more heavy elements they produced.

However, for the first time, we’re detecting deviations from this star-element relationship in the earliest galaxies. This anomaly likely arises from the fact that these galaxies are still in the process of formation, lacking the time needed to generate significant quantities of heavy elements.

Our universe is replete with galaxies, vast assemblages of stars and gas, and as we peer deeper into space, we’re also peering further into the past. Since light takes time to reach us, distant galaxies offer us a unique opportunity to construct a visual narrative of their evolution throughout cosmic history.

Through observations spanning the past 12 billion years, which accounts for five-sixths of the universe’s age, galaxies appear to have maintained a state of equilibrium. There seems to exist a fundamental and precise relationship between the number of stars they’ve birthed and the quantity of heavy elements they’ve synthesized. In this context, “heavy elements” encompasses everything beyond hydrogen and helium.

This relationship is logical, given that the universe initially consisted solely of these two lightest elements. All the elements heavier than hydrogen and helium, including carbon, oxygen, and iron, were forged later by the actions of stars.

Imaging and spectroscopic data of CEERS-z7382. a, False-color JWST/NIRCam red-green-blue image centered on the example galaxy (blue: F150W, 1.5 μm; green: F277W, 2.8 μm; red: F444W, 4.4 μm). The image scale and corresponding physical size at z = 7.8328 is marked. b, Full NIRSpec prism spectrum covering 0.7 μm to 5.2 μm (cyan) and associated 1σ error spectrum (gray). c, Detail of the spectral region covering the nebular emission lines from the [O III] λλ4960, 5008 doublet and Hβ. The local best-fit line and continuum model is shown by the black curve. Credit: Nature Astronomy (2023). DOI: 10.1038/s41550-023-02078-7

James Webb peers deeper

Exploring the universe’s earliest galaxies, those pristine and untouched by heavy elements, has long been an elusive quest due to the challenges of peering back in time. Not only are these galaxies extremely distant, but the prolonged journey of light through space renders it progressively redder. Only with the arrival of the James Webb Space Telescope, a colossal and highly sensitive instrument, have we gained the capability to observe such remote realms.

In a remarkable display, the James Webb Space Telescope has continually shattered its own records by spotting galaxies at unprecedented distances. This achievement brings us closer than ever to the epoch when the very first galaxies came into existence.

A groundbreaking study, recently published in the journal Nature Astronomy on September 21, features a team of astronomers hailing from the Danish research center Cosmic Dawn Center at the Niels Bohr Institute and DTU Space in Copenhagen. Their research has unveiled what appears to be some of the earliest galaxies still in the process of formation.

Kasper Elm Heintz, the study’s leader and assistant professor at the Cosmic Dawn Center, comments on this pivotal development: “Studying the genesis of the first galaxies in the early universe has been nearly impossible until recently, as we lacked the necessary instrumentation. This has undergone a transformative shift with the launch of the James Webb Telescope.”

This plot shows the observed galaxies in an “element-stellar mass diagram”: The farther to the right a galaxy is, the more massive it is, and the farther up, the more heavy elements it contains. The gray icons represent galaxies in the present-day universe, while the red show the new observations of early galaxies. These clearly have much less heavy elements than later galaxies, but agree roughly with theoretical predictions, indicated by the blue band. Credit: Kasper Elm Heintz, Peter Laursen. Credit: Nature Astronomy (2023). DOI: 10.1038/s41550-023-02078-7

Fundamental relation breaks down

The connection between a galaxy’s overall stellar mass and the abundance of heavy elements within it is indeed a nuanced one. The pace at which a galaxy generates new stars also plays a vital role. However, when these factors are appropriately adjusted for, a striking linear relationship emerges: The larger the galaxy, the greater the presence of heavy elements.

But this well-established relationship is now encountering a formidable challenge from recent observations.

Kasper Elm Heintz elaborates, “Upon scrutinizing the light emitted by 16 of these early galaxies, we made a startling discovery. They exhibited a noticeable deficiency in heavy elements, especially when compared to what one would anticipate given their stellar mass and star production rates.”

In fact, these galaxies, on average, possessed only a quarter of the heavy element content found in galaxies from later cosmic epochs. These findings stand in stark contrast to the prevailing model, which posits that galaxies maintain a state of equilibrium for most of the universe’s history.

Predicted by theories

While the outcome may not come as an entirely unexpected revelation, it does align with theoretical models of galaxy formation, meticulously crafted through advanced computer simulations. However, what makes this development groundbreaking is that we’re now witnessing it firsthand.

The authors of the study put forward a rather straightforward explanation: these galaxies are in the midst of their birthing process. Gravity has successfully gathered initial clumps of gas, setting the stage for the birth of stars.

In a scenario where these galaxies evolved undisturbed, stars would swiftly enrich them with heavy elements. However, during this early cosmic era, vast reservoirs of pristine gas flowed between galaxies at a rate surpassing the stars’ ability to keep pace.

As Kasper Elm Heintz notes, “This finding provides us with a remarkable glimpse into the initial phases of galaxy formation, which appears to have a more intricate connection with the intergalactic gas than previously imagined.”

He continues, “These are just the initial observations by the James Webb Telescope on this matter. We eagerly await the results of more extensive and comprehensive observations currently underway. There’s no doubt that we’re on the verge of gaining a much clearer understanding of how galaxies and the earliest structures began forming during the initial billion years following the Big Bang.”

Source: Niels Bohr Institute

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