Using the James Webb Space Telescope (JWST), astronomers have spotted a very bright and mysterious object that could be a galaxy that emerged just 100 million years after the Big Bang, which would make it the oldest known galaxy in the universe, according to a new study.
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Alternatively, Capotauro may be a brown dwarf living on the outer edges of the Milky Way, smoldering at just 27 degrees Celsius. The exact identity of Capotauro is not yet certain, the researchers wrote in the paper, which was published Sept. 1 on the arXiv, but has not yet been peer-reviewed.
Capotauro was first discovered by Giovanni Gandolfi and his team during a previous study in which they tried to identify very old galaxies in James Webb observations. However, the lack of detailed data made it impossible to narrow down the object's identity, which Gandolfi said was like having a small DNA sample at a crime scene but too many matches in the FBI database to be useful.
To determine what Capotauro might be, the team used images taken by JWST's NIRCam at seven wavelengths as part of the Cosmic Evolution Early Release Science (CEERS) to measure Capotauro's brightness. The object was only detected at the two longest wavelengths of NIRCam.
They then used limited, but more detailed data from James Webb's NIRSpec Spectrograph to get a more precise picture of Capotauro's age and temperature.
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Combining the NIRCam and NIRSpec data, the researchers used models to test three possible galaxy configurations, as well as a scenario in which Capotauro could be a brown dwarf on the outer rim of the Milky Way. They also tested a number of other possible scenarios, such as the object being a very strange young galaxy or a peculiar exoplanet.
The results were inconclusive, meaning the team couldn't determine Capotauro's identity with certainty. However, they did identify the two most likely options.
According to the early galaxy interpretation, Capotauro was consistently found to have formed about 100 million years after the Big Bang—shifting the age of the oldest known galaxy back by about 200 million years. It was estimated to be gigantic, with over a billion solar masses.
The other possibility is that Capotauro is a very unusual brown dwarf. If that's the case, Capotauro would be the coldest and most distant brown dwarf known in our galaxy, at a distance of more than seven light-years and just 27 degrees Celsius, the researchers wrote in the study. If Capotauro is a virgin brown dwarf, Gandolfi said, scientists now have an opportunity to probe the formation of our galaxy.
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Both possibilities are "very exciting" because they would challenge what we thought we knew about our own galaxy and about how galaxies form and evolve in general, Gandolfi added.
