Researchers from Scuola Normale Superiore and the University of Ljubljana, in collaboration with international experts, have made a groundbreaking discovery about the evolution of cosmic dust properties in galaxies in the early Universe, using data from the James Webb Space Telescope (JWST).
PISA, 09 January 2025. Cosmic dust is made up of tiny solid particles and it is a fundamental component of galaxies. It plays a crucial role in star formation by facilitating the formation of molecular gas clouds. Furthermore, the cosmic dust absorbs and scatters (and eventually re-emits) light photons from stars in galaxies, depending on their wavelength. This process, known as attenuation, is described mathematically by an attenuation curve, which depends on the dust properties (e.g., grain size and chemical composition) and its spatial distribution relative to stars in a galaxy. Despite its importance, little is known about how dust affects light emitted from the earliest galaxies.
By analyzing the JWST data from 173 distant galaxies formed when the Universe was only 400 million to 3 billion years old (redshift z = 2–12), the team uncovered new insights into how dust influences galaxy light during these early epochs. These findings shed light on the dust properties and spatial distributions within some of the most distant galaxies ever observed.
One of the study’s key discoveries is the identification of a specific ultraviolet (UV) absorption feature, known as the "UV bump", in the attenuation curves of these galaxies. Remarkably, the UV bump was detected in a galaxy from just 700 million years after the Big Bang (z∼7.55), marking the earliest known observation of this feature. The UV bump is thought to result from small dust grains containing organic materials, such as carbon.
The study revealed that dust attenuation curves in early galaxies are generally flatter than those seen in the local Universe, indicating that dust had a less significant impact on the observed light from these distant galaxies. This flatter shape suggests that dust in the early Universe was dominated by larger grains, likely produced in remnants of supernova explosions triggered by the deaths of young massive stars. Over cosmic time, smaller grains became increasingly prevalent, as they underwent processing in the interstellar medium, leading to the steeper attenuation curves and emergence of UV bumps, as observed in nearby galaxies, including the Milky Way.
These findings provide crucial insights into the life cycle of cosmic dust, its evolution over billions of years, and the pivotal role of early supernovae in seeding the Universe with dust. The paper is published in Nature Astronomy and is available at the following link: