As part of its space missions, the James Webb Space Telescope (JWST) is expected to locate the first galaxies, or those that host or have hosted metal-free stellar objects, also known as Population III stars. Surprisingly, one of the most distant galaxies it has detected showed strong metal lines.
At the University of Hertfordshire, Professor Chiaki Kobayashi of the Centre for Astrophysics Research (CAR) led a groundbreaking research using the data obtained from James Webb Space Telescope. His team investigated the GN-z11, a galaxy located only 440 million years after the Big Bang.
The spectra taken by James Webb Space Telescope from GN-z11 indicated an unusually high abundance of nitrogen, something that has surprised many scientists. The result of their study is discussed in the paper "Rapid Chemical Enrichment by Intermittent Star Formation in GN-z11."
Mystery of Nitrogen Abundance
It was hypothesized that only light elements were produced during the Big Bang. Carbon and heavier elements were made in stars and were distributed in the interstellar medium when the stars died after 13.8 billion years of cosmic time.
Until now, one of the theories suggests that the presence of high amounts of nitrogen in the galaxy was the element production from a supermassive star which could be 50,000 to 100,000 times more massive than our sun. Another theory puts forward the idea about the presence of a remnant supermassive black hole.
Breakthrough in Cosmic Mystery
According to Professor Kobayashi, the galaxy is not telling us about an unusual star, but an unusual episode of galaxy life. They discovered that early galaxies have 'bursty' star formation, causing the unusual chemical composition. The bursty star theoretical model helps astronomers unlock understanding of the early universe.
In the brief period of their model estimated as only one million years, the abundance of nitrogen is much more enhanced than oxygen. Their theoretical model does not require any special enrichment sources just as with common stars in the Milky Way galaxy. It predicts all elemental abundances which cannot be detected even with the best telescope we have now.
The model used by Professor Kobayashi suggests that GN-z11 is experiencing an intermittent, bursty star formation. It also indicates that fairly massive dying stars known as Wolf-Rayet stars produce nitrogen before major heavy elements like oxygen are produced by supernovae. As the model witnesses a highly dramatic evolutionary phase for galaxies like GN-z11, this discovery can help scientists gain more insight into the formation of the universe.
The investigation made by the team did not only negate the hypothesis of supermassive stars and supermassive black holes. It has also introduced a new framework for understanding new galaxies.
In the future, the research team would like to investigate what the discovery means for astrophysics. They aim to discover many more galaxies like GN-z11 with unusual chemical composition.
Moreover, they also want to spot more elements in these galaxies aside from nitrogen and nitrogen. Since various elements are produced from different types of stars on different timescales, the elemental abundance patterns serve as a fossil record to help understand the history of the universe. Professor Kobayashi calls this approach 'extra-galactic archaeology.
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