Galaxies so distant that we observe them as they were when the Universe was between 0.6 and 5 billion years old: this is what the James Webb Space Telescope (JWST) has made it possible to see. A feat because today, as our Universe is 13.7 billion years old, the observations of this study date back just 680 million years after the Big Bang.
The cluster of galaxies SMACS0723 – in the photo at the top of the article – has particularly interested scientists who study the moments closest to the beginning of the Universe, including Dr. Miroslava Dessaugesastrophysicist at the Geneva Observatory: “The galaxies analyzed are ‘lensed’, i.e. they are behind a cluster of galaxies which acts like a magnifying glass: this is called a gravitational lens. They are not only brighter than in reality, but we see them with more detail because we gain in angular resolution“, she told RTSinfo.
Training seen on a small scale
The study published in January in the Monthly Notices of the Royal Astronomical Society is interested in star formation at the smallest scales: the Hubble telescope not being able to distinguish them. But thanks to the JWST, we had a finer observation: it is an incredible revolution in the quality of the images”, enthuses Miroslava Dessauges.
“Thanks to the combination of the performance of this new telescope and the magnifying effect of galactic clusters, we will be able to better understand the genesis of stars, as we observe the regions of individual star formations in galaxies at the very beginning of the Universe. .” Scientists thus go back in time and get closer to the millions of years that followed the Big Bang.
>> Ancient globular clusters – the small pink circles – visible thanks to the JWST (right image); Hubble does not distinguish them (left):
Comparison of a place where there are old globular clusters (the little pink circles). On the left, Hubble does not see them; on the right, they are visible thanks to the JWST. [DR]
The team examined eighteen galaxies at varying distances: in astronomy, we speak of different redshifts (read box). “The Hubble Space Telescope had already highlighted a star formation peak at a redshift of 1 and 2 [soit entre 5,9 et 3,3 milliards d’années, ndlr]. JWST gives us further details on this area of interest: star-forming regions and globular clusters are more clearly distinguishable from each other.”
The astrophysicist is delighted to be able to observe the first phase of star formation in distant galaxies, i.e. very small structures, globular clusters: “We see large lumps up to 7 billion years old, or half the age of the Universe. It will be interesting to determine whether these star-forming regions changed properties over time.”
The oldest galaxy analyzed in scientific paper is so distant that astronomers are looking at what it looked like 13 billion years ago, when the Universe was only 680 million years old.
Molecular gas pipelines
The properties of galaxies also change with time: “The younger they are, the richer they are in molecular gas. The more molecular gas there is, the more turbulence there is: therefore, galaxies are more unstable and fragment. The gas condenses and, thus, the stars are created, light up”, says Miroslava Dessauges. “An overdensity in galaxies helps to create more stars. But how did these particularly dense and massive clusters form? It is not yet understood.”
A visualization of cosmic filaments thanks to the Illustris simulation program. Here, the dark matter density is superimposed on the gas velocity field. [ – www.illustris-project.org]
So close to the beginnings of the Universe, scientists did not expect to see so many clusters per galaxy because, until now, observations showed that the number of galaxies possessing them decreased with large redshifts, the redshift: “But there, it’s systematic”, underlines the astrophysicist.
“Did everything go very quickly after the Big Bang? Our numerical simulations show that there are no large galaxies that are born all at once. There are like gas pipelines: filaments that bring the gas in one place and it ends up forming a galaxy.”
galactic storms
The science teams will look at how stars have been created across galaxies over time: “To form stars, you need a lot of molecular gas; and at these big redshifts, these gas pipelines were very The protogalaxies were undoubtedly disturbed by this massive influx of gas, as if there had been a storm.”
And with large masses of gas which contracted, a burst of stars was born: “We finally see the clusters of stars less than a billion years after the Big Bang: they are more massive and denser than the ones we see today.”
Stephanie Jaquet