Little red dots, a population of distant and still poorly understood objects, may be surrounded by small, dense galaxies containing about 1 billion solar masses of material. New observations from the James Webb Space Telescope suggest these galaxies are actively forming stars, while the little red dots themselves may sit at their centers as supermassive black holes.
Little red dots are small, red objects seen at great distances, but scientists still do not know exactly what they are or what produces their light. Earlier observations had found ultraviolet emission around some of them that could point to surrounding galaxies. Optical observations, however, had provided little evidence of such extended material. That matters because optical light gives a clearer view of stellar mass.
Xuheng Ding, Lilan Yang and colleagues looked for this faint signal by combining James Webb Space Telescope images of 217 little red dots. Instead of examining each object separately, they combined the images to detect extended optical emission that was too faint to stand out clearly in individual observations.
Their modeling indicates that the extended light most likely comes from star-forming galaxies. In this interpretation, the little red dots lie at the centers of those galaxies as supermassive black holes.
The galaxies are unusually compact
The galaxies inferred from the data have average radii of about 210 parsecs, or roughly 685 light-years. According to the researchers, that makes them about 2.5 times more compact than other star-forming galaxies with similar masses observed at a comparable period in the universe’s history.
The galaxies are estimated to have total masses around 1 billion times that of the sun.
These observations suggest the little red dots are not simply isolated points of light. Instead, they likely reside within compact, star-forming galaxies, providing clues about how the objects developed during the first billion years after the Big Bang.
Most individual objects remain too faint
The result applies to the sample as a whole. The extended emission is too faint to be detected around most individual little red dots, so the observations describe their average properties rather than confirming the surrounding galaxy in every case.
The researchers also say more work is needed to confirm the sample spectroscopically. Analyzing the objects’ light in this way would help verify their distances.
The study was published in Nature Astronomy.
