Using the James Webb Space Telescope (JWST), astronomers have "weighed" a sleeping giant — a dormant supermassive black hole located a staggering 10 billion light-years away. That makes this black hole the most distant supermassive black hole scientists have ever measured the mass of.
The supermassive black hole is located at the heart of the galaxy MRG-M0138, which is seen as it was when the universe was just around 4 billion years old — and we now know, thanks to the James Webb Space Telescope (JWST), that it weighs an incredible 6 billion times the mass of the sun.
Supermassive black holes can be very conspicuous when actively feeding and therefore surrounded by a wealth of matter in a region called an active galactic nuclei (AGN). Because of the black hole's immense gravitational forces, an AGN glows very brightly. However, because black holes are surrounded by a light-trapping boundary called an event horizon, dormant black holes with larders that aren't quite so well stocked are far more elusive. They're practically invisible. Still, even these black holes have gravitational influences that can impact more than the swirling platters of gas and dust — that influence can also affect the motion of stars orbiting the black holes. And those stars are indeed visible.
To detect and measure the mass of this supermassive black hole, the team behind this research used the JWST to track the motion of stars at the heart of MRG-M0138. This star-tracking trick has been used in the past to weigh dormant black holes much closer to Earth — for example, the 4.3-million-solar-mass supermassive black hole at the heart of our own galaxy, Sagittarius A* (Sgr A*). However, Sgr A* and its attendant stars are just 26,000 light-years away, and the most distant black hole this technique, called stellar dynamics, had been used to weigh was located just 700 million light-years away. At about 15 times that previous record-holding distance, this new research is the first time it has been successfully employed to measure the mass of such a distant sleeping giant.
"Determining how stars collectively move within the core of this distant galaxy has allowed us to measure the mass of its otherwise undetectable supermassive black hole," team leader and University College of London scientist Richard Ellis said in a statement. "By demonstrating the feasibility of such a technique for galaxies in the early universe, we can now undertake a more complete census of how black holes develop over time and infer their role in shaping galaxy evolution."
However, determining the motion of the stars at the heart of MRG-M0138 was anything but straightforward. It required a natural cosmic phenomenon known as gravitational lensing, which emerged from Albert Einstein's magnum opus theory of gravity, known as general relativity.
What is gravitational lensing?
General relativity predicts that objects with mass create an actual curvature in the fabric of spacetime, the four-dimensional unification of the three dimensions of space and the one dimension of time. Gravity emerges from this curvature, and because the larger the mass, the greater the curvature, the larger the mass of an object, the stronger its gravity.
Gravitational lensing occurs when a massive object such as a galaxy or a cluster of galaxies sits between a more distant foreground object and Earth. As light from a background source passes the curvature of space caused by the massive foreground object, or gravitational lens, its usually straight path becomes curved.
The closer to the gravitational lens light passes, the more its path is diverted, and that means that light from the same object reaches our telescopes at different times. This can magnify the object and, in extreme cases, can make the same object appear multiple times at different positions in the same image.
The gravitational lensing effect of a galaxy between MRG-M0138 and Earth refocused the light from that distant galaxy, magnifying it by 30 times, allowing Ellis and colleagues to intricately reconstruct the internal details of MRG-M0138.
"By combining JWST data with gravitational lensing, we could peer inside the black hole’s sphere of influence, where its gravity boosts the speeds of stars," Andrew Newman of Carnegie Science in Pasadena, California, said. "This is one of the best techniques we have to weigh a black hole, so we were excited to extend it to a much earlier period in cosmic history."
In addition to investigating this dormant black hole, the team also determined that MRG-M0138 itself is dormant, meaning it is no longer forming new stars. This is likely the result of the supermassive black hole undergoing a ravenous feeding frenzy earlier in its history when it would have appeared as a blazing quasar at the heart of an AGN. The energy released during this phase would have pushed gas and dust away from both the black hole, ending its feeding phase, and from MRG-M0138 itself. This would deplete the galaxy of the raw material for star formation, thus quenching its stellar birth rate.
This means that with these observations, and with more JWST dormant supermassive black hole data, scientists can better understand the relationship between galaxy growth and supermassive black hole growth, as well as the role these cosmic titans play in cutting off star formation in their host galaxies.
The team's research was published on Thursday (June 4) in Science.
