The James Webb Space Telescope has made a remarkable discovery in a galaxy situated in the early Universe less than 1.5 billion years after the Big Bang. Astronomers have been able to detect complex molecules in the galaxy known as SPT0418-47, from light that traveled for over 12 billion years. The molecules, known as polycyclic aromatic hydrocarbons (PAHs), are found in the clouds that move between stars and re-emit light at infrared wavelengths. The dust containing PAHs is indicative of a high rate of star formation in the galaxy, which is not surprising for a galaxy of this early Universe epoch. However, the dust is unevenly distributed, signifying that the star formation can be mapped to different locations within the galaxy.
The team of researchers, led by Justin Spilker of Texas A&M University, has been able to make detailed observations of a distant galaxy, which is an exciting development. They discovered that the emission from PAH molecules and large dust grains differed due to localized processes within early galaxies. The high equivalent width of the PAH feature indicates that star formation dominates the infrared emission throughout the galaxy instead of black hole accretion.
The Significance of Polycyclic Aromatic Hydrocarbons
Polycyclic aromatic hydrocarbons might sound like a complex term, but they are not rare. On Earth, they are present in soot, which is a common compound. They are a class of organic compounds that contain a ring of carbon atoms that can form during the compression and heating of organic matter. PAHs are present in coal, smoke, smog, and crude oil. The origins of PAHs can be non-biological, and most of the PAHs in the Universe are non-biological. Around 15 percent of all carbon between stars in galaxies like ours is bound up in PAHs, and they are floating between the stars as dust in the interstellar medium. PAHs are considered a reliable tracer of star formation.
While PAHs have been detected in other galaxies, finding them in faraway galaxies is challenging. These molecules absorb light and re-emit it in infrared wavelengths, and previous infrared telescopes had limited sensitivity and coverage. However, the James Webb Space Telescope has made it possible to detect these molecules in very faraway galaxies since it is the most powerful space telescope ever built, strongest in infrared wavelengths.
The Role of Gravitational Lensing
The James Webb Space Telescope had to use gravitational lensing to make a detailed observation. Gravitational lensing is a gravitational curvature of space-time that happens around massive objects like galaxies and galaxy clusters. Any light that passes through such an object becomes warped, magnified, and sometimes duplicated. This allows telescopes to use these lenses as a sort of cosmic magnifying glass, which adds a lot of power to their abilities.
Between the galaxy SPT0418-47 and the telescope is another galaxy at a distance of approximately 3 billion light-years, providing the necessary lensing ability. The TEMPLATES Early Release Science program enabled the telescope to observe the galaxy and, through the lensing effect, get enough detail to allow Spilker and his colleagues to detect the spectral signature of the light emitted by PAHs at a mid-infrared wavelength of 3.3 micrometers. This discovery is the most distant detection of complex aromatic molecules to date.
Although much is still unknown about the reason for the uneven distribution of PAHs throughout the galaxy, this discovery bodes well for future studies of the evolution of galaxies in the early Universe. It is a remarkable discovery that shows the power of advanced technology and the possibilities that await us in the future.
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