Astronomers may have solved one of the main mysteries discovered by the James Webb Space Telescope (JWST). The subject is the so-called "little red dots" - compact bright objects that appear in the early Universe as tiny red specks. According to a new study published in The Astrophysical Journal Letters, these objects may be the birthplaces of the first supermassive black holes.
Since JWST began operating, astronomers have discovered hundreds of such dots. They resemble nothing predicted by previous theories: their size is only a few hundred light-years across, but their brightness is comparable to that of far larger galaxies. In addition, their spectra (the distribution of radiation by wavelength) have an unusual V-shape, and no X-ray or radio emission is detected from these objects. This left specialists baffled.
The authors of the work used complex cosmological modeling. It showed that the little red dots are most likely primordial galaxies with massive black holes at their centers. These holes could have formed from the collapse of supermassive primordial stars. Importantly, the black hole remains enveloped in a huge gas disk that gave rise to it. This gas hides most of the hole's activity from observations.
According to the model's estimates, the mass of such black holes is about 10 million solar masses. The dense gas around them blocks high-energy X-ray radiation but lets through part of the ultraviolet, visible and infrared light. This naturally reproduces the unusual light signatures that JWST sees. In addition, a large cluster of stars nearby in the same small galaxy provides the blue part of the spectrum - this explains another long-standing feature of the little red dots.
The modeling also showed that these systems contain dense clusters of about 100 million stars packed into an area about 500 light-years in diameter. This matches what astronomers observe in real little red dots.
Various explanations had been proposed before: compact star clusters, heavily obscured black holes, supermassive stars and even hypothetical exotic objects such as "black hole stars." However, none of these ideas could fully explain their formation, prevalence, lifetime and unusual spectra. The new model successfully reproduces the properties of a wide variety of little red dots, including some of the most distant and extreme.
"What makes this discovery so exciting is that we may be witnessing the birth of the first supermassive black holes," the press service quotes the head of the study, Daniel Whalen of the Institute of Cosmology and Gravitation at the University of Portsmouth, as saying. "For decades, modeling predicted that such objects should exist, and now the James Webb Space Telescope may finally allow us to see them."
It should be emphasized: these are the results of computer modeling that best explains the observations, not direct proof. Further research is needed to confirm the conclusions.