Mystery solved? A distant X-ray object provides crucial clues to the mystery of the “little red dots” – reddish glowing points of light in the early cosmos that do not match any known class of cosmic objects. Now, for the first time, astronomers have discovered such a “Little Red Dot” that emits X-rays. This supports the assumption that these objects are maturing supermassive black holes surrounded by a dense cocoon of gas.
The “Little Red Dots” (LRD) were already visible in the first images taken by the James Webb Space Telescope (JWST). These compact objects, which glow brightly in the infrared, existed 500 to 700 million years after the Big Bang, but their characteristics do not match any known cosmic phenomenon: the red dots are too compact and bright for an early galaxy, and the typical X-rays are missing for an active supermassive black hole.
Are the red dots “black hole stars”?
“The little red dots cannot be detected in the X-ray range, and they remain weak even in stacked images,” explain Raphael Hviding from the Max Planck Institute for Astronomy in Heidelberg and his colleagues. “At the same time, they lack the strong mid-infrared spectral signatures that we would expect from a hot dust torus.” Therefore, the objects do not fit an active black hole shrouded in dust.
But what are these puzzle objects then? “According to a new theory, the Little Red Dots are active galactic nuclei that are not embedded in dust, but in dense, optically opaque gas,” explain Hviding and his team. These growing black holes therefore have a gas shell similar to a star and are therefore also referred to as “black hole stars”. But if this theory is correct, then there should be transitional forms between these early objects and the later supermassive black holes that have consumed their gas envelope.
A Little Red Dot with X-rays
Astronomers may have now discovered such a transitional form for the first time. The object, named 3DHST-AEGIS-12014, is located around 11.8 billion light-years away from us. In images taken by the NIRspec instrument on the James Webb Telescope, it shows typical characteristics of a Litte Red Dot, including the reddish glow and the lack of dust signature. “Unlike the LRDs, however, it is remarkably bright in the X-ray range,” report Hviding and his colleagues. This was shown in images taken by the Chandra X-ray telescope of this object.
“This X-ray red dot therefore represents a unique combination of features that does not fit into the standard classification,” explain the astronomers. “Although its high X-ray luminosity and spectral shape would normally clearly identify it as an active galactic nucleus, it also bears striking resemblance to the Little Red Dot population.” The team used models to investigate what this could be.
Transition stage with perforated gas shell
The result: The strange features of 3DHST-AEGIS-12014 are best consistent with a transition shape from a small red dot to a classic supermassive black hole. The black hole growing in the center of the dense gas envelope could gradually consume the gas, creating thinned areas in the gas cocoon. “As a result, the gas envelope still dominates the optical continuum, but X-rays can escape through some optically thinner areas,” explain the astronomers.
This is consistent with the fact that the X-ray intensity of the object in the Chandra data changes slightly over time. These changes could arise because the thinned areas of the gas envelope rotate around the black hole, which means that sometimes more or less X-rays can penetrate.
(Video:
Chandra X-ray Observatory)
“Strongest evidence to date”
“If it is confirmed that this X-ray Red Dot actually represents a transitional form, then not only would it be the first of its kind, we would also have seen the heart of such a Little Red Dot for the first time,” says co-author Hanpu Li from Princeton University. “We would then have the strongest evidence yet that there is a growing supermassive black hole hidden inside some, if not all, Litte Red Dots.”
This means that the newly discovered “red X-ray dot” could be the crucial piece of the puzzle of the small red dots. “The “This object literally allowed us to connect the dots.”
Source: Raphael Hviding (Max Planck Institute for Astronomy, Heidelberg) et al., The Astrophysical Journal Letters, 2026; doi: 10.3847/2041-8213/ae4c88