Scientists around the world have analyzed the first data collected by the James Webb Space Telescope unveiled on July 12. A Geneva team shows that the oldest galaxies are much more evolved than the models predicted. And it’s a surprise!
Scientists from the Geneva Observatory have scrutinized around a hundred very old galaxies spotted in images taken by the James Webb Space Telescope (JWST). Galaxies so close to the time of the Big Bang, a founding event that took place 13.8 billion years ago…
For the first time, the team has identified the chemical composition of two of them, visible between 600 and 700 million years after the Big Bang – those framed in yellow in the image at the top of the article. Their study was prepublishedin order to be available to the scientific community.
“The first surprise is the spectacular oxygen signature in the very first observations of the JWST”, notes, enthusiastically, the first author of the study, Daniel Schaerer, of the Geneva Observatory. “The data shows that these distant galaxies are already much more evolved than predicted by computer-generated astrophysical models,” he adds, answering RTSinfo by telephone.
Scientists are delighted with this unexpected discovery. Unheard of – Hubble could not measure spectra of such distant galaxies – which was possible thanks to the tremendously powerful spectrography instruments on board the JWST, including the NIRSpec instrument (read box). This measures theof the targeted object: the spectrum obtained gives information on the age and the chemical composition of the galaxies.
>> The emission spectrum taken by NIRSpec of a galaxy located 13.1 billion years ago:
The first spectroscopy of the composition of a distant galaxy given by the NIRSpec instrument on the James Webb Space Telescope. [NIRSpec Emission Spectrum/JWST – NASA, ESA, CSA, STScI]
>> The same spectrum in a more scientific version, used in the published study:
The spectrum of a galaxy obtained with NIRSpec. The vertical dashed lines mark the position of well-detected nebular emission lines. [Daniel Schaerer et al., 22 juillet 2022 – Astronomy & Astrophysics]
A history of chemistry
The most common chemical elements in the Universe – the lightest and also the simplest – are hydrogen and helium: “When these gases fuse together inside stars, they end up producing more complex elements – and heavier ones – like carbon, nitrogen, oxygen or neon,” Prof. Schaerer explains.
These elements, scientists were not expecting already some 600 million years after the Big Bang: “In a galaxy that has not evolved much, there have not yet been many generations of stars… and these are the ones that are massive which produce the heavy chemical elements. They eject them: the oxygen produced, for example, then goes into the next generation of stars”.
“At this extremely distant time, the chemical composition had never been measured!”, Underlines the astrophysicist. “In addition, the abundance of oxygen – about ten times less than in the Sun – shows that matter has been recycled very quickly. These galaxies evolve very quickly, giving life to many stars. Stars that have a very short lifespan: this is how they produce oxygen”.
An evolution to clarify
From now on, scientists will have to work to understand how the chemical composition of these distant galaxies evolves and at what speed the different heavier chemical elements appear.
“Heavy elements are a sign of production by the stars. When we see carbon, nitrogen, oxygen, we know that there has been great stellar activity. A star like our Sun, of low mass, lives nine billion years: it evolves slowly. It therefore has little effect on the chemical composition of its galaxy”, further indicates Daniel Schaerer.
“It’s the short-lived stars that produce oxygen. And it takes a lot of it to start a new cycle of star generation.”