Since the James Webb Space Telescope began sending its first scientific observations in 2022, tiny, extremely red objects called "Little Red Dots" by astronomers have appeared in the early universe and have quickly become one of the most exciting mysteries of the early universe.
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But a team of researchers decided not to stare at these objects themselves, but rather to look at what surrounds them. Using images from the James Webb Space Telescope of 217 tiny red dots, the scientists were able to gather extremely faint signals from their surroundings, revealing for the first time direct evidence of host galaxies around them in optical light.
A new and perplexing cosmic phenomenon known as "Little Red Dots" are very distant objects that appeared in images of the early universe, and scientists still do not know their true nature.
A new and perplexing cosmic phenomenon known as “Little Red Dots” are very distant objects that appeared in images of the early universe, and scientists still do not know their true nature (NASA).
The results indicate that these galaxies are unusually small and compact, and that they may offer a key to understanding the conditions under which the small red dots appeared during the first billion years of the universe's existence.
A mystery that emerged with James Webb
Small red dots are a group of distant, compact objects that appeared in James Webb Space Telescope observations of the early universe. They are characterized by their red color and small size, and they exhibit optical and spectral properties that do not quite fit the conventional picture of galaxies or active galactic nuclei.
Several studies suggest that small red spots are associated with supermassive black holes at their centers, but their precise nature and how they were formed are still a subject of debate.
The mystery is compounded because these objects appear to be relatively common in the early universe, then almost disappear in later cosmic eras. Therefore, most previous studies have focused on the intense light source at the center of each point, but this has made discovering the host galaxy extremely difficult, because the brightness of the center overwhelms the faint light surrounding it.
Smaller galaxies than expected
Instead of studying each individual dot, the team used a technique based on stacking images of 217 tiny red dots taken by the James Webb near-infrared camera, allowing them to collect and highlight the faint light shared between them.
Because of that technique, faint, extended components appeared around the points in a certain range of infrared radiation, with a typical size of about 200 parsecs, or about 650 light-years, at a redshift of about 6.5.
By analyzing light in four bands, the researchers estimated the average stellar mass of the host galaxies to be about one billion solar masses. Surprisingly, this is about 2.5 times smaller than typical star-forming galaxies of similar stellar mass from the same cosmic era.
This means that the stellar matter in these galaxies is crammed into a much smaller space, which may make their environment denser than usual.
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