The light of stars around primordial quasars offers clues to the formation of supermassive black holes

The quasar J0148+0600
An article published in “The Astrophysical Journal” reports the results of observations of primordial quasars that indicate that supermassive black holes form from “seeds” that are very massive and grow quickly. A team of researchers used observations conducted with the James Webb Space Telescope as part of the EIGER project to detect the faint light of the stars surrounding three of those quasars. This feat offers the possibility of obtaining much more information that allows to estimate the mass of galaxies and central supermassive black holes.

The estimates obtained for the three galaxies at the center of this study indicate that the primordial supermassive black holes were much more massive than today’s supermassive black holes compared to their host galaxies. According to the researchers’ reconstruction, primordial quasars powered by black holes engulfed materials at enormous speeds as they went from initial seeds to supermassive black holes.

The image (Courtesy Minghao Yue et al 2024) shows the quasar J0148+0600, one of the three objects of this study, circled in red observed by the James Webb Space Telescope. The two insets show the supermassive black hole (top) that powers it and the stellar emissions from the galaxy that hosts it (bottom).

The EIGER (Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization) project aims to explore the evolution of intergalactic gas and galaxies in the so-called Epoch of Reionization. That’s the crucial period in the history of the universe when light started spreading freely throughout space. Six primordial galaxies were the subject of observations in particular with the NIRCam (Near Infrared Camera) instrument of the James Webb space telescope, whose power and sensitivity allowed unprecedented results to be obtained.

Quasars are powered by supermassive black holes that heat the materials around them to the point of generating very strong electromagnetic emissions. This makes them visible even at a distance of 13 billion light-years but makes it extremely difficult to distinguish the light of the quasar from that of the stars of a galaxy hosting a quasar. The quasars covered by the EIGER project were observed intermittently from autumn 2022 to spring 2023 for a total of over 120 hours of observations.

Even with the James Webb Space Telescope, detecting the starlight of those primordial galaxies is very difficult but the authors of this study managed to do it for three galaxies. The amount of light obtained from the quasar and stars offers the possibility of estimating the mass of the supermassive black hole and stars in each of those galaxies.

The result of the estimates indicates that in those primordial galaxies, the mass of the supermassive black hole was about a tenth of the mass of the galaxy that hosts it. That’s a very different result compared to a recent galaxy, where the mass ratio is 1:1000.

Astronomers have long been wondering if the supermassive black hole grows first and the galaxy follows, or the opposite occurs resulting in the growth of the supermassive black hole. This study suggests that in the early universe, supermassive black holes grew faster than their host galaxies. This behavior could be a clue that the initial seeds of supermassive black holes may have been more massive at the time. This would explain how such colossal objects could have formed so quickly in the early universe.

This study shows the potential of the James Webb Space Telescope in near-infrared observations of primordial galaxies hosting quasars. New observations, also of other primordial quasars, will help improve analysis models and obtain new information on the formation of supermassive black holes. It’s a study that intersects with that of the influence of these truly extreme objects on the galaxies that host them and in particular on star formation.

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