Early galaxies may have been larger and more complex than previously thought

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[EN VIDÉO] Radio astronomy captures distant galaxies that give birth to stars
Thanks to the International Low Frequency Array (LOFAR), a vast network of 70,000 radio telescopes spread across Europe, astronomers have obtained breathtaking images of the youth of our universe. Tens of thousands of galaxies trapped as they formed stars. This video suggests flying over a part of the explored sky. © Jurgen de Jong, Leiden University

A1689-zD1 is the name there astronomers give to a young galaxy is about 13 billionlight years of ours The Milky Way. a galaxy “normal” whereupon astronomers pointed to the large millimeter / submillimeter antenna array of Atacama (Alma, Chile) in hopes of revealing its secrets. And as they report on the occasion of the congress of the American Astronomical Union, they were not disappointed.

They have actually discovered a halo of carbon cold that surprisingly extends far beyond the center of the A1689-zD1. As well as streams of gas hot and ionized from the heart of the young galaxy. Such discharges are usually the result of violent activity, such as supernova. All this could be proof of that stars formed there, continuously. Especially since carbon halide is found in the same regions ashydrogen neutral interstellar known for concentrating in the regions of star formation. So the A1689-zD1 could turn out to be much larger than astronomers thought.

It is also possible that this carbon halo is a remnant of previous galactic activity. A1689-zD1 could thus already have experienced mergers. Of gravitational forces complexes would then have exerted themselves on the galaxy, leading to the ejection of a colossal amount of gas over these great distances. But in both cases, the A1689-zD1 probably underwent a fairly active early development. “And even if it had never been observed, it could be what happens most of the time, for the first galaxies formed in our Universe»comments Hollis Atkins, lead author of the study, in a statement of National Radio Astronomy Observatory (United States).

Rififi in the primitive universe

Seiji Fujimoto, another author of these works, confirms this: “The carbon halide in A1689-zD1 is much more extensive than what was observed with The Hubble Space Telescope, and this may mean that the first galaxies are not as small as they appear. This would have a major impact on the theory of galaxy formation and evolution inPrimitive universe. »

Why did the Hubble Space Telescope not see anything? For he does not look in the field radio , available in Alma. Because here the astronomers also randomly took advantage of a gravitational lensing effect, which made it possible to magnify the target galaxy more than nine times. Enough to reveal critical details that usually remain hidden from such distant galaxies.

Looking at it from another eye – and also closer – it therefore seems that the first galaxies that appeared in our universe were already very complex. That the early universe was not quite as the astronomers had drawn it. Thus, researchers are now awaiting with undisguised impatience the observations planned by James Webb Space Telescope(JWST). From January 2023, they were to take an even more complete look at the A1689-zD1.

A very young galaxy from the beginning of the universe and already dusty

The universe was then only 700 million years old, but this young galaxy A1689-zD1, very distant, therefore, and spotted by the VLT, was already rich in dust. Its detailed observation of Alma was made possible by a gravitational lensing effect and confirms the rapid evolution of galaxies born shortly after. big bang .

Article byESO published on 09/03/2015

A team of astronomers led by Darach Watson from the University of Copenhagen used the instrument X shooting game installed on the VLT by Eso as well as Alma – a large (sub-) millimeter array by Atacama – to observe one of galaxiesthe youngest and most distant. To their surprise, the goal seemed very advanced to them. In fact, the proportion of dust it contains is similar to the proportion of a mature galaxy The Milky Way . This essential component contributes to the formation of planets, moleculescomplexes and normal stars.

Galaxy A1689-zD1, identified in previous snapshots by space telescope Hubble, was the target of their observations. A gravitational lens effect produced by Abell 1689 a spectacular a cluster of galaxies located on the line of sight, increased its brightnessapparently by a factor of 9. In the absence of this effect, the young galaxy with low brightness could not have been detected.

To observe A1689-zD1 is to examine part of the universe, which at that time was only 700 million years old (ie 5% of its current age). This system is modest in appearance – much less massive and luminous than many other objects in the young universe previously studied – and therefore more representative of galaxies dating from this period, genionization . All first stars then generated one dawn cosmic, illuminates for the first time a large and transparent universe, thus ending the period of stagnation known as the dark age.

The chemical complexity as well as the abundance of interstellar dust in this galaxy surprised the observers, who expected to discover a very young system. “After the VLT confirmed that the galaxy was moving away, we realized that it had already been observed using Alma.says Darach Watson. We did not expect to find much, but I can tell you that we were all very excited at the thought that Alma had taken an accurate snapshot. One of the main purposes of this observatory is to detect emissionsof cold gas and dust from galaxies in the young universe – and we had one! »

This young galaxy quickly generated stars

This galaxy is a child of cosmos , but an early child. At her age she should be missing chemical elementstung (in metalsas we in astronomy denote the elements heavier than hydrogen andhelium ). These metals are produced in the hearts of stars and then spread out into space when e.g. at the end of its lifestar explode. Repeated over many generations of stars, this process leads to the significant enrichment of the universe in heavier elements such as carbon,oxygenandnitrogen .

Surprisingly, the galaxy A1689-zD1 appeared to emit intense radiation ininfrared distant (the initial radiation, converted to millimeter waves by the expansion of the universe, can be detected by Alma). This suggested that it had already given birth to many stars and produced significant amounts of metals. Thus, it not only contained a good deal of dust, but it was characterized by a dust / gas ratio similar to that of more mature galaxies. “Although the exact origin of galactic dust remains unknown, our observations suggest that its production began very early, within 500 million years after the beginning of star formation in the universe – a time frame very short on the cosmological scale, knowing that most stars for billions of years “specifies the researcher who led this study published in the March 2, 2015 issue of Nature(also available here on ESO’s website).

The results suggest that the galaxy A1689-zD1 either continuously created new stars at a moderate speed beginning 560 million years after the Big Bang, or went through a very intense star-creation phase followed by a period of decline.

Prior to this study, astronomers feared they would not be able to detect galaxiesso far away that way. The case of A1689-zD1 shows that it is possible to detect it using short observations made with Alma.

“This incredibly dusty galaxy appears to be busy feeding its first generation of starscomments Kristen Knudsen from Chalmers University of Technology (Sweden), who co-authored the article. In the future, Alma will allow us to discover other galaxies of this type and will reveal to us the secret behind their haste. »

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