A picture of James Webb could help understand the complex chemistry of the universe

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Last week, the James Webb Space Telescope unveiled its first shots. Among these a unique infrared image of the universe, the deepest and sharpest to date. This image of the SMACS 0723 galaxy cluster is packed with details. In particular, we can see a distant galaxy with a red background from the early universe. The telescope’s NIRSpec spectrograph has provided the spectrum that reveals the composition of its gas: these unprecedented data may help to understand the chemical evolution of the universe in its early stages.

Of the thousands of distant galaxies behind the SMACS 0723 galaxy cluster, NIRSpec observed 48 individually, all at once, in a field roughly the size of a grain of sand held at arm’s length. These galaxies have been observed as they existed in the early universe. Their emission spectra show similarities: all have a hydrogen line followed by two ionized oxygen lines; the position of this pattern on the spectrum makes it possible to estimate the redshift of galaxies and thus their distance. One of these galaxies has been identified as the most distant.

This obscure little red dot is a galaxy as it was 13.1 billion years ago. It is now the most distant galaxy about which we know the chemical elements », tweeted Emma Chapman, astrophysicist and fellow of the Royal Society based at Imperial College London. Thanks to James Webb, scientists have access for the first time to the chemical composition of the very first galaxies in the universe. Comparing their spectra will determine how they have evolved over billions of years.

A characteristic emission pattern

The galaxy cluster SMACS 0723 appeared to us as it was 4.6 billion years ago. But it acts as a gravitational lens and has made it possible for scientists to observe much more distant galaxies, which existed at very early times in the history of the universe – estimated to be 13.8 billion years old.

James Webb’s NIRSpec spectrograph has identified the chemical composition (bottom) of a galaxy that emitted light 13.1 billion years ago. This galaxy is among thousands observed on the telescope’s first deep field image. © NASA, ESA, CSA, STScI

NIRSpec (Near-infrared spectrograph) is a multi-object dispersive spectrograph operating in the near infrared. It was built by Astrium (a subsidiary of EADS) for the European Space Agency. This instrument can simultaneously observe over 100 objects (stars and galaxies) within a 3’x3 ‘field of view. It is the first instrument ever sent into space that has this capability. Thanks to him, scientists were able to determine the spectra of certain galaxies.

These spectra reveal the chemical composition, temperature and density of ionized gas in galaxies. This 13.1 billion year old galaxy emits characteristic lines of oxygen, hydrogen and neon – including a specific pattern consisting of a hydrogen line followed by a double oxygen line that scientists discovered in each of the targeted galaxies. ” This is how the oxygen to our bodies was made in the stars of galaxies, and we see this process taking place said Jane Rigby, James Webb Project Scientist at NASA’s Goddard Space Flight Center, at a news conference.

The NIRSpec team was particularly surprised to have such a detailed spectrum for this first observation of the deep universe. They were hoping to observe an oxygen emission line, but thought they would have to target dozens or even hundreds of objects before they could detect it.

Unraveling the chemical processes of dark times

This oxygen line is particularly important because astronomers use it to calibrate their measuring instruments; it acts as a kind of standard. This practice is common for the study of nearby galaxies, but no scientist had been able to apply it to distant galaxies until now. Now the team will be able to interpret the apparent appearance of different chemical fingerprints in a spectrum to the amounts of chemicals present in the targeted galaxy.

The future spectra of other distant galaxies provided by James Webb will thus make it possible to study the evolution over time of the proportions of the various chemical elements. This is important for achieving one of the intended scientific goals: to fill the gaps associated with the beginning of the universe. In fact, between about 380,000 years after the Big Bang and about a billion years after, scientists have very little information.

This era corresponds to the dark age of the universe followed by reionization. The universe was just a diffuse mixture of hydrogen and helium that gradually came together to form the first galaxies that gave birth to the first generation of stars. However, due to the lack of data at this time, the processes involved are still the subject of debate. James Webb is able to directly explore this mysterious period. Soon, the telescope will observe even more distant galaxies, which can finally illuminate all the chemistry of the universe.

Source: Webb Space Telescope

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