Scientists around the world have analyzed the first data collected by the James Webb Space Telescope, unveiled on July 12. A team in Geneva shows that the oldest galaxies are much more developed than the models predicted. And it’s a surprise!
Scientists from the Geneva Observatory have scrutinized about a hundred very old galaxies seen in images taken by the James Webb Space Telescope (JWST). Galaxies so close to the time of the Big Bang, a fundamental event that occurred 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 – the ones framed in yellow in the image at the top of the article. Their investigation was premeditatedto be accessible to the scientific community.
“The first surprise is the spectacular oxygen signature in the very first observations of JWST,” enthuses the first author of the study, Daniel Schaerer of the Geneva Observatory. “The data show that these distant galaxies are already much more evolved than predicted by computer-generated astrophysical models,” he adds, answering RTSinfo by phone.
Scientists are delighted with this unexpected discovery. Unheard of – Hubble could not measure spectra of such distant galaxies – which was possible thanks to the enormously powerful spectrography instruments aboard JWST, including the NIRSpec instrument (read box). This measuresof the targeted object: the obtained spectrum provides information on the age and 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 provided 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 – such as carbon, nitrogen, oxygen or neon ,” explains Prof. Schaerer.
These elements the scientists did not expect already around 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 it is the massive ones that produce heavy chemical elements. They expel 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!”, emphasizes 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 and give life to many stars. Stars that have a very short lifetime: that’s how they produce oxygen”.
A development to clarify
From now on, scientists must work to understand how the chemical composition of these distant galaxies evolves and at what rate the various heavier chemical elements appear.
“Heavy elements are a sign of stellar production. When we see carbon, nitrogen, oxygen, we know that there has been great stellar activity. A low-mass star like our Sun lives for nine billion years: it evolves slowly. It therefore has only little effect on its chemical composition of its galaxy”, says Daniel Schaerer.
“It’s the short-lived stars that produce the oxygen. And it takes a lot of it to start a new cycle of star generation.”