Astronomers have successfully identified and quantified an unprecedentedly massive black hole, registering a mass of 36 billion solar masses. This particular ultramassive celestial object approaches the theoretical maximum mass capacity within the observable cosmos and dwarfs Sagittarius A*, the supermassive black hole at our Milky Way’s core, by approximately 10,000 times.
This Hubble image illustrates the Cosmic Horseshoe gravitational lens system (positioned towards the right of center). The recently identified ultramassive black hole is situated at the heart of an orange galaxy. Behind it, a blue galaxy is distorted into a horseshoe-shaped ring due to spacetime warping caused by the formidable mass of the preceding orange galaxy. Image attribution: NASA / ESA / Hubble.
The recently cataloged ultramassive black hole is integrated within the Cosmic Horseshoe gravitational lens system, where the lensing galaxy itself ranks among the most substantial strong gravitational lenses ever documented.
This extensive lens system, also designated as SDSS J1148+1930 and CSWA 1, is situated at a cosmological distance of 5 billion light-years, within the celestial expanse of Leo.
“Ordinarily, for such distant cosmic structures, determining black hole mass is feasible only when the black hole is actively feeding,” stated Carlos Melo, a doctoral candidate at the Universidade Federal do Rio Grande do Sul.
“However, estimations derived from accretion processes frequently carry considerable margins of error.”
“Our methodology, which synergistically combines strong lensing analysis with stellar dynamics, furnishes a more direct and reliable mass determination, even for these remote celestial entities.”
“The black hole we’ve recently found ranks among the top ten most massive black holes ever recorded, and quite possibly holds the title for the most massive,” commented Professor Thomas Collett from the University of Portsmouth.
“A significant portion of other black hole mass evaluations are indirect and are burdened by substantial uncertainties, leaving us without definitive confirmation of which is truly the largest. Nevertheless, our novel approach has afforded us a far greater degree of certainty regarding the mass of this particular black hole.”
The research team employed a dual approach, integrating both gravitational lensing observations and stellar kinematics, to pinpoint the Cosmic Horseshoe black hole.
While stellar kinematics is generally regarded as the benchmark for measuring black hole masses, its application is effectively limited to the immediate cosmic neighborhood due to the diminishing apparent size of galaxies in the observable universe, making it impossible to resolve the region hosting a supermassive or ultramassive black hole.
“The incorporation of gravitational lensing enabled us to extend our observational reach considerably further into the cosmos,” Professor Collett explained.
“We observed the black hole’s influence in two distinct ways: it demonstrably bends the trajectory of light passing nearby, and it induces exceptionally high velocities (approaching 400 km/s) in the stellar population within the inner confines of its host galaxy.”
“By corroborating these two independent measurements, we have achieved unequivocal confidence in the existence and mass of this black hole.”
“This particular discovery pertains to a ‘dormant’ black hole – one that was not actively consuming matter at the time of our observation,” Melo elaborated.
“Its detection was solely attributable to its profound gravitational influence and the resultant impact on its surrounding environment.”
“What is particularly significant is that this technique empowers us to detect and quantify the masses of these concealed ultramassive black holes throughout the universe, regardless of their current state of activity.”
A notable characteristic of the Cosmic Horseshoe system is that its host galaxy is classified as a fossil group.
Fossil groups represent the terminal evolutionary stage of the most gravitationally cohesive structures in the universe, formed when these massive conglomerations coalesce into a single, exceptionally large galaxy, devoid of any smaller, luminous satellite galaxies.
“It is highly probable that all the supermassive black holes originally residing in the companion galaxies have subsequently merged, culminating in the ultramassive black hole we have identified,” Professor Collett hypothesized.
“Consequently, we are witnessing the culmination of both galactic and black hole evolution.”
The research findings have been formally published today in the esteemed journal, the Monthly Notices of the Royal Astronomical Society, accessible via the following link.
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Carlos R Melo-Carneiro et al. 2025. Unveiling a 36 billion solar mass black hole at the centre of the Cosmic Horseshoe gravitational lens. MNRAS 541 (4): 2853-2871; doi: 10.1093/mnras/staf1036
