Astronomers using the NASA/ESA/CSA James Webb Space Telescope have spotted a galaxy with a never-before-seen light signature — indicating that its gas is outshining its stars. Found approximately one billion years after the Big Bang, this galaxy — labeled JADES-GS+53.12175-27.79763 (GS-NDG-9422 hereafter) — may be a missing-link phase of galactic evolution between the Universe’s first stars and familiar, well-established galaxies.
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Detailed information on the chemical makeup of GS-NDG-9422, captured by Webb’s NIRSpec (Near-Infrared Spectrograph) instrument, indicates that the light we see in this image is coming from the galaxy’s hot gas, rather than its stars. Image credit: NASA / ESA / CSA / STScI / A. Cameron, University of Oxford.
“My first thought in looking at the galaxy’s spectrum was, ‘that’s weird,’ which is exactly what Webb was designed to reveal: totally new phenomena in the early Universe that will help us understand how the cosmic story began,” said Dr. Alex Cameron, an astronomer at the University of Oxford.
Dr. Cameron and colleagues found that computer models of cosmic gas clouds heated by very hot, massive stars, to an extent that the gas shone brighter than the stars, was nearly a perfect match to Webb’s observations.
“It looks like these stars must be much hotter and more massive than what we see in the local Universe, which makes sense because the early Universe was a very different environment,” said Dr. Harley Katz, a theoretical astrophysicist at the University of Oxford and the University of Chicago.
In the local Universe, typical hot, massive stars have a temperature ranging between 40,000 to 50,000 degrees Celsius.
According to the researchers, GS-NDG-9422 has stars hotter than 80,000 degrees Celsius.
They suspects that the galaxy is in the midst of a brief phase of intense star formation inside a cloud of dense gas that is producing a large number of massive, hot stars.
The gas cloud is being hit with so many photons of light from the stars that it is shining extremely brightly.
In addition to its novelty, nebular gas outshining stars is intriguing because it is something predicted in the environments of the Universe’s first generation of stars, which astronomers classify as Population III stars.
“We know that this galaxy does not have Population III stars, because the Webb data show too much chemical complexity,” Dr. Katz said.
“However, its stars are different from what we are familiar with — the exotic stars in this galaxy could be a guide for understanding how galaxies transitioned from primordial stars to the types of galaxies we already know.”
At this point, GS-NDG-9422 is one example of this phase of galaxy development, so there are still many questions to be answered.
Are these conditions common in galaxies at this time period, or a rare occurrence?
What more can they tell us about even earlier phases of galaxy evolution?
The authors are actively identifying more galaxies to add to this population to better understand what was happening in the Universe within the first billion years after the Big Bang.
“It’s a very exciting time, to be able to use the Webb telescope to explore this time in the Universe that was once inaccessible,” Dr. Cameron said.
“We are just at the beginning of new discoveries and understanding.”
The team’s paper was published in the Monthly Notices of the Royal Astronomical Society.
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Alex J. Cameron et al. 2024. Nebular dominated galaxies: insights into the stellar initial mass function at high redshift. MNRAS 534 (1): 523-543; doi: 10.1093/mnras/stae1547
This article is based on a press-release from NASA.
