James Webb reveals the presence of oxygen in the first galaxies – rts.ch

Scientists around the world analyzed the first data collected by the James Webb Space Telescope that opened on July 12. A group in Geneva showed that the oldest galaxies are more evolved than predicted models. And this is a surprise!

Scientists from the Geneva Observatory have analyzed nearly a hundred ancient galaxies seen in images taken by the James Webb Space Telescope (JWST). Galaxies were very close at the time of the Big Bang, a founding event that occurred 13.8 billion years ago…

For the first time, the team identified the chemical composition of two of them, which appear 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 previously published on the arXiv websiteto be available to the scientific community.

“The first surprise was the unique signature of oxygen in the first observations of JWST”, says enthusiastically, the first author of the study, Daniel Schaerer, of the Geneva Observatory. “The data show that these distant galaxies are much more evolved than predicted by computer-generated astrophysical models,” he added, responding to RTSinfo by phone.

Scientists are delighted with this unexpected discovery. Unheard of – Hubble cannot measure the spectra of such distant galaxies – which is possible thanks to the more powerful spectrography instruments aboard JWST, including the NIRSpec instrument (read the box). It measures the spectral shift of the target object: the spectrum obtained 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]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 combine inside the stars, they result in the creation of more complex elements – and heavier – like carbon, nitrogen, oxygen or neon,” explained Prof. Schaerer.

These elements, scientists did not expect about 600 million years after the Big Bang: “In a galaxy that has not evolved much, there have not been many generations of stars … heavy chemical elements. They release them: the oxygen produced, for example, then goes to the next generation of stars”.

“In this extremely distant time, the chemical composition has not been measured!”, Lines the astrophysicist. “Furthermore, the abundance of oxygen – about ten times less than the Sun – indicates that the matter was recycled very quickly. These galaxies grew very quickly, giving life to many stars. Stars that are short very life: this is the way. they make oxygen”.

An evolution to be clear

From now on, scientists must try to understand how the chemical composition of these distant galaxies evolved and how quickly the various heavier chemical elements appeared.

“Heavy elements are a sign of the production of stars. If we see carbon, nitrogen, oxygen, we know that there is a lot of activity in the star. A star like our Sun, with less that weight, lives nine billion years: it evolves slowly. So it has little effect on the chemical composition of its galaxy”, Daniel Schaerer added.

“These are short-lived stars that produce oxygen. And it takes a lot of them to start a new cycle of star generation.”

Stephanie Jaquet

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