Three growing massive black holes appear to coexist in a single galaxy, observed when the Universe was only about 1.2 billion years old.
This galaxy, called J0148-4214, lies at a redshift of 5.0167. This measurement indicates that its light has been significantly stretched by the expansion of the Universe. Astronomers therefore see it as it was very early in cosmic history. The James Webb Space Telescope made it possible to examine its light with sufficient precision to distinguish several very compact regions.
Pixabay illustration
The researchers did not photograph the black holes directly. They studied the light emitted by gas rotating rapidly around them before falling toward their centers. This gas produces, among other things, a spectral line associated with hydrogen. When it appears very broad, it reveals high speeds near a massive object that is absorbing matter.
Two of these regions lie at the heart of the galaxy. They are separated by only about 190 parsecs, or nearly 620 light-years. A third appears farther away, about 1.7 kiloparsecs from the center, or roughly 5,500 light-years. Such an arrangement provides rare insight into the growth of black holes in young galaxies.
The estimated masses are very different. The largest central black hole would reach about 80 million times the mass of the Sun. Its neighbor would be close to 630,000 solar masses. The third, located outside the center, would approach two million solar masses. These values remain estimates obtained from the gas velocity and luminosity.
To understand the significance of this configuration, we need to return to galaxy formation. In the young Universe, galaxies frequently approached one another and merged. Their black holes could then end up together in the same system. Observations of J0148-4214 provide access to a stage in which several of these objects still appear distinct and active.
The authors examined other possible explanations for the observed emissions, including supernovae, fast winds, and very massive stars. Their analysis nevertheless favors the presence of three regions powered by black holes. For the two central objects, their small separation strengthens the hypothesis of a gradual approach driven by gravity.
According to an estimate based on their motion within the galaxy, the two central black holes could eventually merge in less than 700 million years. The third could then join the center, but its history remains uncertain.
Future observations will need to determine whether this system could become a source of gravitational waves detectable by space observatories planned for the coming decades.