The James Webb Space Telescope (JWST) has revealed a fascinating and unexpected aspect of the early universe, leaving astronomers with a captivating puzzle to solve. The universe's early galaxies are not what we thought they were.
Just weeks into its observations, the JWST discovered galaxies in the universe's infancy that were far more massive than our theories predicted. These galaxies, dating back to just 600,000 years after the Big Bang, are a mystery that researchers are eager to unravel.
Enter the Atacama Large Millimetre/submillimetre Array (ALMA) and its team of dedicated researchers. Their work, published in the Monthly Notices of the Royal Astronomical Society, offers an explanation for these puzzling early galaxies. The lead author, Tom Bakx, a postdoc at Chalmers University of Technology in Sweden, has delved into the secrets of a galaxy named Y1.
Y1, located at redshift 8.3, is a superheated star factory with an incredibly high star formation rate (SFR). Its SFR is approximately 180 times greater than that of the Milky Way, forming 180 solar masses per year compared to the Milky Way's mere 1. This extraordinary rate of star formation challenges our existing theories and provides a potential explanation for the unexpected size of early galaxies.
Yoichi Tamura, an astronomer at Nagoya University in Japan, adds, "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 JWST's images of these early galaxies reveal their brightness, suggesting a mass far greater than previously believed. As Tom Bakx explains, "What we see in Y1 is red light from superheated dust, which masks its high SFR. We're looking back to a time when the universe was making stars much faster than today."
ALMA's observations in Band 9, at a wavelength of 0.44 mm, allowed researchers to measure the temperature of Y1's dust. At around 90 Kelvin (-180 Celsius), Y1's dust is significantly warmer than the Milky Way's, which is around 20 to 40 Kelvin. This temperature difference reflects the higher SFR in Y1 compared to the relatively stable star formation in the Milky Way.
But here's where it gets controversial: if rapid bursts of star formation are common in the early universe, they could explain the JWST's discovery of massive galaxies at such an early stage. Even brief episodes of elevated SFR could account for this phenomenon.
And this is the part most people miss: the research also reveals that early galaxies may contain far more dust than expected. Older stars, especially evolved red giants, are the primary producers of galactic dust. However, if the dust is warmer than anticipated, it can be just as luminous as a smaller amount of cooler dust. Thus, a large population of evolved stars is not necessary to explain the observed dust.
Laura Sommovigo, a co-author from the Flatiron Institute and Columbia University, explains, "Galaxies in the early universe seem 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 authors conclude that this extreme example of dust-obscured star formation contributes significantly to the cosmic build-up of stellar mass, a phenomenon that can only be fully understood through comprehensive observations in the (sub)mm regime.
So, what do you think? Are we witnessing a new understanding of the early universe, or is there more to uncover? The universe's secrets are waiting to be revealed, and the JWST and ALMA are our guides on this exciting journey.
