The main aim of the JADES program is to make in-depth observations of galaxies that are very far away, and therefore also very old (because looking far into space is like looking far back in time: sunlight takes 8 minutes to reach us, for example, so we see it as it was 8 minutes ago), using the JWST's infrared capabilities to see objects that have remained undetected by other telescopes. The two letters “GS” in the galaxy's name refer to the region of the sky in which the galaxy was observed: indeed, “GS”-type galaxies are located in the GOODS-South region. GOODS (Great Observatories Origins Deep Survey) is an observing campaign that employs several of the world's largest telescopes: Hubble, Spitzer, Chandra, JWST... to observe two very specific regions of the sky: GOODS-North (GN) and GOODS-South (GS). The GOODS-South region is located in the constellation Fornax, a less luminous constellation in the Southern Hemisphere, chosen for its low density of nearby stars and its visibility to telescopes in space. Finally, let's finish exploring the meaning of this wonderful galaxy's complex name, with the therme “z14-0”. The letter z is used to designate the redshift value of the object in question, in this case 14. As explained in the article on dark matter, which you can consult here: The dark matter.
Therefore, redshift is a phenomenon that corresponds to the Doppler effect, a shift between the wavelengths emitted by the object and those observed by the observer, who is fixed in comparison with the moving object. This shift occurs either towards shorter wavelengths, which corresponds to blue, the blueshift, and means that the object is approaching, or towards longer wavelengths, which corresponds to red, the redshift, and means that the object is moving away. The redshift is determined by: z = (observed lambda - emitted lambda) / emitted lambda. (don't thank me for this little formula ;) ) With lambda the wavelength of light. A redshift of 14 means that the lambda of the galaxy's light has been stretched to 15 times its original wavelength (1+14 =15 (yeyy) ). So the higher the redshift, the further away the object is from us (easy that way!). A redshift of the order of 14 places JADES GS-z14-0 among the most distant and ancient objects ever observed. A redshift of 14 indicates that the light we receive from this galaxy traveled for around 13.5 billion years before reaching us. This light therefore comes from a time very close to the Big Bang, when the universe was extremely young, around 300 million years after its formation. What's more, due to the incessant expansion of the universe, this galaxy is now even further away from us than the distance the light traveled to reach us!
In this way, this galaxy provides crucial information about the early universe, in particular the formation of the first galaxies and stars, and the evolution of the early universe. The discovery of JADES GS-z14-0 provides information that, in some aspects, challenges or refines our theoretical models of the early universe. Firstly, cosmological models predicted that the first galaxies would form gradually, that they would be relatively small and low-mass in the first few hundred million years after the Big Bang, and that the reionization of the universe was mainly due to these numerous small galaxies emitting sufficient light to ionize the surrounding gas.
A brief explanation of the reionization of the universe: (The reionization of the universe is a key period in cosmic history when the universe went from a state where light was blocked to a state where light could travel freely. After the Big Bang, the universe was very hot and ionized (electrons and protons were separated).
Around 380,000 years after the Big Bang, the universe cooled enough for protons and electrons to combine and form neutral hydrogen atoms, making the universe “dark” because light couldn't travel freely. Hundreds of millions of years later, the first stars and galaxies formed and began emitting intense ultraviolet light. This light re-ionized neutral hydrogen (re-separating protons and electrons), making the universe transparent to light. And then, tadaam, the universe is ionized again, hence the reionization!).
Nevertheless, JADES GS-z14-0 appears to be relatively massive and luminous for a galaxy formed only 300 million years after the Big Bang. This suggests that the formation of massive galaxies may have occurred more rapidly than expected, and the presence of such luminous and well-developed galaxies at this stage of the universe suggests that the reionization of the universe may have been influenced by more massive galaxies than previously thought. Furthermore, theories assumed that the rate of star formation in the early universe would be modest, due to the still young and turbulent conditions. On the other hand, our galaxy has a high star formation rate, which is surprising given its age. This could imply that early galaxies were able to form stars much more efficiently than expected. Also, the first galaxies must have been composed mainly of hydrogen and helium, with very few heavier elements (metals), as these elements are produced by the first generations of stars. However, observations may indicate a more rapid metallization (presence of heavier elements) than expected. This suggests that the first stars enriched their environment with metals quite rapidly, which may have favored the formation of new stars and complex galaxies.
Overall, JADES GS-z14-0 offers the opportunity to refine, readjust and challenge our cosmic models. The discovery of this galaxy truly opens a window on the early universe.
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Leia Desautel