Diamonds in the sky: James Webb Telescope’s discovery rewrites early galaxy evolution”

In a groundbreaking discovery, the James Webb Space Telescope has captured the chemical signature of carbon-rich dust grains in the early universe. These same signatures were previously observed in more recent parts of the universe and were believed to be associated with complex carbon-based molecules called polycyclic aromatic hydrocarbons (PAHs). However, researchers are skeptical that PAHs could have formed within the first billion years of cosmic time.

An international team of astronomers, including researchers from the University of Cambridge, proposed an alternative explanation. They suggest that the James Webb Telescope might have observed a different type of carbon-based molecule, possibly minute graphite- or diamond-like grains that were produced by the earliest stars or supernovas. If true, this discovery implies that infant galaxies in the early universe developed much faster than previously thought.

Cosmic dust, composed of various-sized grains, plays a crucial role in the evolution of the universe. It serves as the building blocks for new stars and planets. However, dust can obscure our observations of certain regions of space by absorbing stellar light at specific wavelengths. Fortunately, astronomers can deduce the composition of cosmic dust by studying the wavelengths of light it blocks.

The team of astronomers led by Cambridge used this technique and the James Webb Telescope’s remarkable sensitivity to detect the presence of carbon-rich dust grains only a billion years after the universe’s birth. These grains are highly effective at absorbing ultraviolet light at around 217.5 nanometers, which was observed directly in the spectra of very early galaxies for the first time.

Previous observations in more recent times have associated the 217.5-nanometer feature with two different types of carbon-based molecules: PAHs and nano-sized graphitic grains. However, given that PAHs are not expected to form until several hundreds of millions of years later, the researchers suggest that the observed carbon-rich dust grain might be something else entirely.

The observed feature in the early universe peaked at 226.3 nanometers, slightly different from the 217.5-nanometer wavelength linked to PAHs and tiny graphitic grains. This discrepancy could be due to measurement error, or it might indicate a different composition of cosmic dust in the early universe.

According to the researchers, this slight shift in wavelength might indicate the presence of graphite- or diamond-like grains, possibly formed by Wolf-Rayet stars or ejected material from supernovas. Models have previously proposed the formation of nano-diamonds in supernova ejecta, and the short lifespan of Wolf-Rayet stars might have allowed enough time for carbon-rich grains to disperse into the surrounding cosmic dust within a billion years.

Despite this exciting discovery, it remains challenging to fully explain these results with the current understanding of cosmic dust’s early formation. The findings will undoubtedly drive the development of improved models and future observations.

The James Webb Telescope, with its unprecedented sensitivity, has revolutionized astronomy. It allows astronomers to make detailed observations of light from individual dwarf galaxies from the first billion years of cosmic time. This capability finally enables the study of cosmic dust’s origin and its role in the critical early stages of galaxy evolution.

The team plans to further investigate the data and its implications, collaborating with theorists who model dust production and growth in galaxies. This research will shed light on the origin of dust and heavy elements in the early universe.

These groundbreaking observations were made as part of the JWST Advanced Deep Extragalactic Survey (JADES), which has led to the discovery of hundreds of galaxies that existed when the universe was less than 600 million years old, including some of the most distant galaxies known to date.

The implications of this discovery are profound, as it challenges existing models of dust formation and provides a new way to study the chemical enrichment of the universe’s earliest galaxies. Astronomers are excited about the possibilities of uncovering more secrets about the universe’s birth and evolution using the James Webb Space Telescope.

Source: University of Cambridge

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