The James Webb Space Telescope (JWST) has made a groundbreaking discovery, revealing galaxies in the early Universe that are significantly more massive than previously theorized. Just weeks into its observational mission, the JWST detected these unexpected cosmic structures, prompting researchers to seek explanations for their size and luminosity. A team utilizing the Atacama Large Millimetre/submillimetre Array (ALMA) has published findings that shed light on this phenomenon, particularly focusing on a galaxy designated Y1.
Significant Findings from ALMA
The research, titled “A warm ultraluminous infrared galaxy just 600 million years after the Big Bang,” appears in the Monthly Notices of the Royal Astronomical Society. Lead author Tom Bakx, a postdoctoral researcher at Chalmers University of Technology in Sweden, explains that Y1 is observed at a redshift of 8.3, indicating that we see it as it was just 600 million years after the Big Bang. The light from Y1 has been traveling for over 13 billion years to reach us today.
Y1 is characterized as a “superheated star factory,” boasting a star formation rate (SFR) approximately 180 times that of our Milky Way, which forms about one solar mass per year. This extraordinary SFR offers a plausible explanation for the unexpectedly large sizes of early galaxies, suggesting that existing theories of star formation may not adequately account for such high rates.
Understanding Dust and Star Formation
The study highlights the pivotal role of light in astronomical observations. The red light from Y1’s superheated dust obscures its high SFR, leading researchers to consider a unique process of star formation. Bakx remarked, “We’re looking back to a time when the universe was making stars much faster than today.” Previous observations indicated the presence of dust in Y1, making it the most distant galaxy from which we have directly detected light from glowing dust.
To confirm their hypotheses, the research team measured the galaxy’s temperature using ALMA, which observes in what is termed Band 9, or light at a 0.44 mm wavelength. Bakx noted that the brightness of Y1 at this wavelength suggested something extraordinary. The galaxy’s dust temperature is approximately 90 Kelvin (or -180 Celsius, -292 Fahrenheit), significantly warmer than that of the Milky Way, which ranges from 20 to 40 Kelvin.
Co-researcher Yoichi Tamura, an astronomer at Nagoya University, stated, “This confirmed that it really is an extreme star factory. Even though it’s the first time we’ve seen a galaxy like this, we think that there could be many more out there.” If rapid bursts of star formation like those seen in Y1 were common, they could explain the JWST’s observations of massive galaxies from the early Universe.
Bakx emphasized the need for further exploration, stating, “We don’t know how common such phases might be in the early Universe, so in the future we want to look for more examples of star factories like this.” The team plans to leverage ALMA’s high-resolution capabilities to investigate Y1’s characteristics in greater detail.
The implications of this research extend beyond the size of early galaxies. It also suggests that early galaxies may contain more dust than previously believed. Traditionally, astronomers have understood that older stars, particularly evolved red giant stars, are the primary sources of galactic dust. However, if the dust is warmer than expected, it can be just as luminous as larger amounts of cooler dust.
Co-author Laura Sommovigo from the Flatiron Institute and Columbia University commented, “Galaxies in the early Universe seem to be too young for the amount of dust they contain. That’s strange, because they don’t have enough old stars, around which most dust grains are created.” This suggests that even young galaxies like Y1 can exhibit significant dust luminosity despite their limited population of heavy elements.
The research concludes that Y1 serves as an extreme example of dust-obscured star formation, contributing to the cosmic buildup of stellar mass. Such discoveries underscore the importance of direct and comprehensive observations in the submillimetre regime, as they reveal new insights into the formation and evolution of early galaxies in the Universe.
