Insights into the Earliest Stages of Galaxy Formation

The Universe is teeming with galaxies — immense collections of stars and gas — and as we peer deep into the cosmos, we see them near and far. Because the light has spent more time reaching us, the farther away a galaxy is, we are essentially looking back through time, allowing us to construct a visual narrative of their evolution throughout the history of the Universe.

The big galaxy in the foreground is named LEDA 2046648, and is seen just over a billion years back in time, while most of the others lie even farther away, and hence are seen even further back in time. Image credit: ESA/Webb, NASA & CSA, A. Martel.

Observations have shown us that galaxies through the last 12 billion years — that is, 5/6 of the age of the Universe — have been living their life in a form of equilibrium: There appears to be a fundamental, tight relation between on one hand how many stars they have formed, and on the other hand how many heavy elements they have formed. In this context, “heavy elements”, means everything heavier than hydrogen and helium.

This relation makes sense, because the Universe consisted originally only of these two lightest elements. All heavier elements, such as carbon, oxygen, and iron, was created later by the stars.

Kasper Elm Heintz, assistant professor at the Cosmic Dawn Center explained:

“Until recently it has been near-impossible to study how the first galaxies are formed in the early Universe, since we simply haven’t had the adequate instrumentation. This has now changed completely with the launch of James Webb.”

 A team of astronomers from the Danish research center Cosmic Dawn Center at the Niels Bohr Institute and DTU Space in Copenhagen, led by Professor Heintz, has discovered what seems to be some of the very first galaxies which are still in the process of being formed.

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 ones clearly have much less heavy elements than later galaxies, but agree roughly with theoretical predictions, indicated by the blue band. Image credit: Kasper Elm Heintz, Peter Laursen.

Professor Heintz continued:

“When we analysed the light from 16 of these first galaxies, we saw that they had significantly less heavy elements, compared to what you’d expect from their stellar masses and the amount of new stars they produced.”

In fact the galaxies turned out to have, on average, four times less amounts of heavy elements that in the later Universe. These results are in stark contrast to the current model where galaxies evolve in a form of equilibrium throughout most of the history of the Universe.

Diffuse gas from intergalactic space plummets toward the center, sparking star formation and becoming part of the galaxy’s rotating disk. When stars die, they return their gas to the galaxy (and the intergalactic space), now enriched with heavy elements. Image credit: Tumlinson et al. (2017).

And he concluded:

“The result gives us the first insight into the earliest stages of galaxy formation which appear to be more intimately connected with the gas in between the galaxies than we thought.

“This is one of the first James Webb observations on this topic, so we’re still waiting to see what the larger, more comprehensive observations that are currently being carried out can tell us.

“There is no doubt that we will shortly have a much clearer understanding of how galaxies and the first structures began their formation during the first billion years after the Big Bang,”

Click on this link to access, Dilution of chemical enrichment in galaxies 600 Myr after the Big Bang, published in Nature Astronomy

2 replies »

  1. Galaxies have always been my thing when our observing. This has produced interesting new information, and just what we should expect. Mind you, it’ll be interesting to see if we can get any similar info from the earliest visible Red Shift galaxies, formed maybe 2-3 billion years after the beginnings of the universe.

Leave a Reply