Spectral analysis of luminous galaxy JADES-GS-z14-0 based on observations made in January 2024 revealed a redshift of 14.32 which makes it the most distant galaxy known (previous most-distant galaxy known was JADES-GS-z13-0 at the redshift of z = 13.2). It was formed in the early universe about 290 million years after the Big Bang. The copious amount of starlight implies it is massive and is over 1,600-light years across in size. Such a luminous, massive and large galaxy in the early universe at cosmic dawn defies current understanding of galaxy formation. The first stars in the universe were Pop III stars with zero-metal or extremely low-metal. However, study of infrared properties of JADES-GS-z14-0 galaxy reveals presence of oxygen which means metal enrichment implying generations of massive stars had already completed their life-courses from births to supernova explosion by about 290 million years in the early universe. Thus, the properties of this galaxy is at odds with the current understanding of galaxy formation in the early universe.
The very early universe, by about 380,000 years after the Big Bang, was filled with ionised gases and was fully opaque due to scattering of photons by the free electrons. This was followed by the neutral epoch of early universe that lasted for about 400 million years. In this epoch, the universe was neutral and transparent. The first light emerged upon universe becoming transparent, became red shifted to microwave range due to expansion, and is now observed as Cosmic Microwave Background (CMB). Because the universe was filled with neutral gases, no optical signal was emitted (hence called dark age). Un-ionized materials do not emit light hence difficulty in study of early universe of neutral epoch. However, microwave radiation of 21 cm wavelength (corresponding to 1420 MHz) emitted by the cold, neutral cosmic hydrogen during this epoch due to hyperfine transition from parallel spin to more stable anti-parallel spin offers opportunities to astronomers. This 21 cm microwave radiation would be redshifted upon reaching earth and will be observed at 200MHz to 10 MHz frequencies as radio waves. The REACH (Radio Experiment for the Analysis of Cosmic Hydrogen) Experiment aims to detect elusive 21-cm line from Cosmic Hydrogen.
The epoch of reionisation was the next epoch in the history of early universe that lasted from about 400 million years after the Big Bang to 1 billion years. The gases became re-ionised due to high energy UV radiations emitted by the powerful early stars. Formation of galaxies and quasars began in this epoch. The lights of this epoch are red shifted to towards red and infrared ranges. Huble deep field studies were a new beginning in study of early universe however its scope in capturing primordial lights was limited. An infrared observatory based in space was needed. JWST specialises exclusively in infrared astronomy to study early universe.
James Webb Space Telescope (JWST) was launched on 25 December 2021. Subsequently, tt was placed in an orbit near the Sun–Earth L2 Lagrange point about 1.5 million km from the earth. It became fully operational in July 2022. Using key scientific instruments onboard such as NIRCam (Near Infrared Camera), NIRSpec (Near Infrared Spectrograph), MIRI (Mid-Infrared Instrument), JWST searches for optical/infrared signals from the early stars and galaxies formed in the Universe for a better understanding of the formation and evolution of galaxies and the formation of stars and planetary systems. In the last two years, it has produced fascinating results in the exploration of cosmic dawn (i.e., the period in the first few hundred million years after the big bang where the first galaxies were born).
JWST Advanced Deep Extragalactic Survey (JADES) programme
This programme aims to study galaxy evolution from high redshift to cosmic noon by way of infrared imaging and spectroscopy in the GOODS-S and GOODS-N deep fields.
In the first year, the JADES researchers came across hundreds of candidate galaxies from the first 650 million years after the big bang. In early 2023, they found a galaxy in their dataset that appeared to be at a red shift of 14 suggesting that must be an extremely distant galaxy but it was very bright. Also, it appeared to be part of another galaxy due to proximity. Hence, they observed that gain in October 2023. The new data supported it being at a red shift of 14. A spectrum of this galaxy was needed for identifying location of Lyman-alpha break in the spectrum to measure the red shift and determine age.
Lyman-alpha is a spectral emission line of hydrogen in the Lyman series when electrons transition from n=2 to n=1. The point of Lyman-alpha break in the spectrum corresponds to observed wavelength (λobserved). The red shift (z) can be calculated as per the formula z = (λobserved – λrest) / λrest
JADES-GS-z14-0 galaxy
Accordingly, the galaxy was observed again in January 2024 using NIRCam (Near Infrared Camera) and NIRSpec (Near Infrared Spectrograph). Spectral analysis provided clear evidence that the galaxy was at a redshift of 14.32, making it the most distant galaxy known (previous most-distant galaxy record (JADES-GS-z13-0 at the redshift of z = 13.2). It was named JADES-GS-z14-0, a luminous galaxy at a distance 13.5 billion light years. Further, it was over 1,600-light years across in size that suggested that young stars are the source of its luminosity. Also, amount of starlight meant it must be very massive. It is not expected of a galaxy existing less that 300 million years after the Big Bang to have such properties. It does not fit well into existing models of galaxy formation.
There were more surprises in store.
Researchers were able to detect JADES-GS-z14-0 at longer wavelengths using MIRI (Mid-Infrared Instrument). This meant capturing visible-light range emissions from this galaxy that were red-shifted to become out of range for near-infrared instruments. Analysis revealed presence of ionised oxygen implying high stellar metallicity. This is possible only when many generations of stars have already lived their life courses.
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.
Considering age of the galaxy JADES-GS-z14-0 is less than 300 million years after the Big Bang, the stars in this galaxy should be Pop III stars with zero-metal content. However, JWST’s MIRI did find presence of oxygen.
In view of the above observations and findings, the properties of the early universe galaxy JADES-GS-z14-0 do not conform to current understanding of galaxy formation. How could a galaxy with such features be dated to 290 million years after the Bing Bang? It is possible that many such galaxies may be discovered in future. Perhaps a diversity of galaxies existed at the Cosmic Dawn.
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References:
- Carniani, S., et al. 2024. Spectroscopic confirmation of two luminous galaxies at a redshift of 14. Nature (2024). Published 24 July 2024. DOI: https://doi.org/10.1038/s41586-024-07860-9 . Preprint at axRiv. Submitted 28 May 2024. DOI: https://doi.org/10.48550/arXiv.2405.18485
- Helton J.M., et al 2024. JWST/MIRI photometric detection at 7.7 μm of the stellar continuum and nebular emission in a galaxy at z>14. Preprint at axRiv. Submitted 28 May 2024. DOI: https://doi.org/10.48550/arXiv.2405.18462
- The NASA James Webb Space Telescope. Early highlights – NASA’s James Webb Space Telescope Finds Most Distant Known Galaxy. Posted 30 May 2024. Available at https://webbtelescope.org/contents/early-highlights/nasas-james-webb-space-telescope-finds-most-distant-known-galaxy
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. It was formed in the early universe about 290 million years after the Big Bang. The copious amount of starlight implies it is massive and is over 1,600-light years across in size. Such a luminous, massive and large galaxy in the early universe at cosmic dawn defies current understanding of galaxy formation. The first stars in the universe Pop III stars with zero-metal or extremely low-metal. However, study of infrared properties of JADES-GS-z14-0 galaxy reveals presence of oxygen which means metal enrichment implying generations of massive stars had already completed their life-courses from births to supernova explosion by about 290 million years in the early universe. Properties of this galaxy is at odds with the current understanding of galaxy formation in the early universe.){kind=link}