Study of image taken by the JWST has led to discovery of a galaxy in the early universe about a billion years after the big bang whose light signature is attributed to its nebular gas outshining its stars. Now named GS-NDG-9422, the galaxy is chemically complex and does not have Population III stars. Similarly, the most distant galaxy JADES-GS-z14-0 formed in the early universe about 290 million years after the Big Bang was found to have metals. As per the current understanding, the first generation of stars of the early universe should be Population III stars with zero metallicity. In astronomy, any element heavier than helium is considered a metal. Chemical non-metals like oxygen, nitrogen etc are metals in cosmological context. Stars get metal enriched in each generation following supernova event.
Using image captured by NIRSpec (Near-Infrared Spectrograph) instrument of James Webb Space telescope (JWST), researchers have identified a unique galaxy from the early universe at a red shift of Z= 5.943 corresponding to approximately one billion years after the big bang. Now named GS-NDG-9422, this galaxy may be a missing-link phase of galactic evolution between the first stars of the universe and well-established galaxies.
The faint dot image of the galaxy GS-NDG-9422 has unique light signature. The source of light seen in the image is galaxy’s hot gas. The light did not come from its stars.
Unlike massive stars in our local universe whose temperature is about 40,000 to 50,000 °C, stars in GS-NDG-9422 galaxy are extremely hot. Perhaps, this galaxy was in star formation stage inside a dense gas nebula producing a large number of massive, hot stars when the light left this galaxy about 12.8 billion years ago to reach the JWST now. The observation fits the computer model that constant bombardment of the nebular gas by the photons of the hot stars heated the nebular gas to more than 80,000 °C enabling it to shine brighter in near-infrared light than the stars.
A galaxy dominated by nebular light (rather than starlight) is in line with environments of the first generation of stars of the early universe. Stars in such galaxies are Pop. III stars with zero metallicity. However, surprisingly, galaxy GS-NDG-9422 does not have Population III stars. JWST data shows that GS-NDG-9422 is chemically complex.
The case of the most distant galaxy JADES-GS-z14-0 formed in the early universe about 290 million years after the Big Bang is still more perplexing. Stars in this galaxy should be Pop. III stars with zero metallicity however, study of infrared properties of JADES-GS-z14-0 galaxy reveals presence of oxygen which means metal enrichment implying generations of stars should have already completed their life- cycles.
The first stars in the universe have zero-metal or extremely low-metal. They are called Pop III stars (or Population III stars). Low metal stars are Pop II stars. Young stars have high metal contents and are called “Pop I stars” or the solar metal stars. With a relatively high 1.4% metallicity, sun is a recent star. In astronomy, any element heavier than helium is considered a metal. Chemical non-metals like oxygen, nitrogen etc are metals in cosmological context. Stars get metal enriched in each generation following supernova event. Increasing metal content in stars indicates younger age.
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References:
- Cameron A.J., et al 2024. Nebular dominated galaxies: insights into the stellar initial mass function at high redshift. Published: 21 June 2024. Monthly Notices of the Royal Astronomical Society, Volume 534, Issue 1, October 2024, Pages 523–543, DOI: https://doi.org/10.1093/mnras/stae1547
- NASA News – In Odd Galaxy, NASA’s Webb Finds Potential Missing Link to First Stars. Avaialble at https://science.nasa.gov/missions/webb/in-odd-galaxy-nasas-webb-finds-potential-missing-link-to-first-stars/
- Prasad U., 2024. Early Universe: The Most Distant Galaxy “JADES-GS-z14-0″ Challenges Galaxy Formation Models. Scientific European. Published 12 August 2024. Available at http://scientificeuropean.co.uk/sciences/space/early-universe-the-most-distant-galaxy-jades-gs-z14-0-challenges-galaxy-formation-models/
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