Is it possible for three supermassive black holes to blaze in radio bright phases all simultaneously? The answer to this question was recently given by astronomers, who confirmed that this is possible in the first known galaxy merger hosting three galaxy nuclei with supermassive, actively accreting, and radio-bright black holes identified as J1218/1219+1035, which is situated some 1.2 billion light years away.
It has come after a process that started with data obtained from the NASA Wide-field Infrared Survey Explorer, WISE, whose mid-infrared color diagnostics pointed out some unusual emission features for a set of two interacting galaxies. These features pointed to the presence of at least two active galactic nuclei, and the features for the closely located third galaxy were ambiguous, with its optical spectrum representing either star-forming activity or a hidden active galactic nucleus. The optical spectroscopy later narrowed the observation to one with three galaxies showing the same redshift, being gravitationally bound, with the distances between them being 22,000 light-years for the first two and 97,000 light-years for the third. Just as expected, these morphologies agree with the outcomes expected for the simulation concerning galaxies separating after a close encounter, to later meet again.
The critical discovery was made by radio interferometry with high resolution. The VLA, with the U.S. National Science Foundation, took images with the highest resolution setting A, at wave frequencies of 3, 10, and 15 GHz, with subarcsecond resolution. Ample VLBA observation at the wave frequency of 4.9 GHz contributed milliarcsecond scales and brightness temperature limits. Having the ability to resolve the cores emitting synchrotron radiation rather than the general galactic radio emission, the observations confirmed radio sources at the same position as the optical nuclei, with the central source having a brightness temperature in excess of 1.7 × 10⁵ K, above the each star-forming region threshold to guarantee an AGN origin.
Spectral index analysis, an essential ingredient in determining emission mechanism signatures, indicates that the two nuclei have spectral indices close to -0.7, typical of synchrotron emission due to relativistic jets, optically thin. The third, J1219+1035, had a steeper index of -1.28, suggestive of jet activity on scales smaller than the resolution limit of 250 parsecs for the Ku band. This is typical of older or more compact jet morphology; hence, this will be indicative of the evolutionary state of each of these AGNs.
This triple AGN is thus the first triple radio AGN, hence the first triple AGN known to produce evidence for active dynamical evolution, hence the first triple AGN known to produce evidence for active evolution via synchrotron radiation. The triple AGN known to the current point in time are few. These few known systems involve triple AGN that are primarily radio quiet or involve triple AGN that have undergone the final stages of the merger. J1218/1219+1035, on the other hand, is in its intermediate stages. This particular triple AGN has distinct tidal features, such as the presence of tidal tails or tidal ridges, or more specifically, the presence of tidal trails or tidal bridges, which are the remains of the stars and gas stripped away by the gravitational pull between the merging object.
These trails or bridges also indicate that the object is dynamically active. These trails or bridges, therefore, indicate that the object is dynamically active, or specifically, they indicate that the object is dynamically active in the sense that the core of each of the triple AGN is producing its share of synchrotron radiation. However, such optical properties can be rendered opaque by dust or gas within the object. The VLA or VLBA, on the other hand, can penetrate such obscurations in the object. This is because the VLA or VLBA can determine the presence of non-thermal cores in the AGN, thus the AGN are dynamically active in the sense that the core of each of the AGN is producing its share of synchrotron radiation. This particular approach also helped determine if the AGN have linear or nonlinear spectra. This, therefore, is the first triple AGN known to produce evidence for active dynamical evolution, hence the first known to produce evidence for active evolution via synchrotron radiation.
A triple AGN is thus a natural laboratory for the study of AGN feedback, or the manner by which the radiation or outgases of the accreting AGN interact with the surrounding gas to heat the gas or expel the gas. This, in particular, is generally in the study of the manner by which the radiation or outgases of the AGN interact with the surrounding gas to control star formation in the object. The AGN, on the other hand The triple activity in J1218/1219+1035 suggests the possibility of cumulating feedback effects as a result of the complex interaction of several jet systems and the common interstellar medium.
Future observations will expand the time baseline. Near-infrared imaging will provide higher-resolution maps of tidal features, while X-ray observations will test high levels of high-energy activity from each individual AGN that may result from differences in accretion rates or obscuration. Expanding the current sample of confirmed triple radio AGN using a combination of mid-infrared searches and deep radio observations will improve estimates of black hole merger rates and make model predictions of gravitational wave events that will become detectable with the advent of the upcoming LISA mission more accurate.
As Dr. Emma Schwartzman, lead astronomer on this research, explains: It’s the transition from theory to reality. With our observation that all three black holes in this system are radio-bright and active jet-ejectors, we can say that the theory of triple radio AGN is no longer just a theory that is, a reality that is purely theoretical but a reality that is purely real. It’s a whole new window into supermassive black hole life cycles. To the community of astronomers and astrophysicists, however, the system of J1218/1219+1035 is far more interesting ıt is not merely an extremely rare occurrence that signifies an alignment of giants but is instead a dynamic multi-wavelength marker that illuminates the intricate movement of so-called galactic co-evolution that characterizes the supermassive black hole universe.
