The James Webb Space Telescope (JWST) has made groundbreaking discoveries about the early universe, revealing galaxies that challenge existing astronomical theories. Just weeks into its observations, the JWST identified massive galaxies that were unexpected in their size and brightness. These findings have prompted researchers to seek explanations, with a new study from the Atacama Large Millimetre/submillimetre Array (ALMA) offering insights into one such galaxy, designated Y1.
Published in the Monthly Notices of the Royal Astronomical Society, the research is led by Tom Bakx, a postdoctoral researcher at Chalmers University of Technology in Sweden. The study focuses on Y1, which exists at a redshift of 8.3, meaning it is observed as it was approximately 600 million years after the Big Bang. The light from this galaxy has been traveling for over 13 billion years, providing a glimpse into a formative period of the universe.
Y1 is characterized as a “superheated star factory” due to its extraordinary star formation rate (SFR), which is about 180 times greater than that of the Milky Way. While the Milky Way forms roughly one solar mass of stars per year, Y1 is producing around 180 solar masses annually. This unprecedented rate suggests that early galaxies were much larger than previously theorized, as conventional models of star formation do not accommodate such high SFRs.
The findings indicate that the light observed from Y1 is red light emitted by superheated dust, which obscures its high star formation rate. “We’re looking back to a time when the universe was making stars much faster than today,” Bakx stated in a press release. “Previous observations revealed the presence of dust in this galaxy, making it the furthest away we’ve ever directly detected light from glowing dust.”
To further understand Y1, researchers utilized ALMA to measure the galaxy’s temperature. By observing at a wavelength of 0.44 mm in Band 9, they discovered that Y1’s dust temperature is about 90 Kelvin (approximately -180 Celsius or -292 Fahrenheit). In comparison, the Milky Way’s dust temperature ranges between 20 to 40 Kelvin. This significant difference reflects the galaxies’ distinct star formation rates, with Y1’s higher temperature indicating its intense activity.
Co-researcher Yoichi Tamura, an astronomer at Nagoya University in Japan, remarked, “Even though it’s the first time we’ve seen a galaxy like this, we think that there could be many more out there. Star factories like Y1 could have been common in the early universe.”
The implications of Y1’s rapid star formation may clarify why the JWST has uncovered massive galaxies so early in cosmic history. If such intense bursts of star formation were indeed common, they could account for the unexpected size and brightness of early galaxies. Bakx emphasized the need for further exploration, stating, “In the future, we want to look for more examples of star factories like this. We also plan to use the high-resolution capabilities of ALMA to take a closer look at how this galaxy works.”
Beyond explaining galaxy size, this research also addresses the unexpectedly high levels of dust found in early galaxies. Traditionally, astronomers believe that older stars, particularly evolved red giants, are the primary sources of galactic dust. However, if the dust is warmer than previously thought, a smaller amount can be just as luminous as a larger quantity of cooler dust.
Co-author Laura Sommovigo from the Flatiron Institute and Columbia University noted, “Galaxies in the early universe seem to be too young for the amount of dust they contain. But a small amount of warm dust can be just as bright as large amounts of cool dust, and that’s exactly what we’re seeing in Y1.”
The research concludes that Y1 serves as an extreme example of dust-obscured star formation that significantly contributes to the cosmic build-up of stellar mass. These revelations are made possible through direct and comprehensive observations in the submillimetre regime, opening new avenues for understanding the evolution of galaxies in the early universe.
