Supermassive black holes may slow star formation not only in their own galaxies but also in neighbouring galaxies, suggesting they may have played a much larger role in shaping galaxy evolution in the early Universe than previously thought.
Intense radiation emitted by active supermassive black holes – thought to reside at the centre of most galaxies – can slow star growth not just in their host galaxy, but also in galaxies millions of light-years away, according to a new study.
“Traditionally, people have thought that because galaxies are so far apart, they evolve largely on their own,” explained Yongda Zhu, a postdoctoral researcher at the University of Arizona Department of Astronomy and Steward Observatory who led the study.
“However, we found that a very active, supermassive black hole in one galaxy can affect other galaxies across millions of light-years, suggesting that galaxy evolution may be more of a group effort.”
Destructive nature of supermassive black holes affects star growth
Zhu explained that this is known as the “galaxy ecosystem”, and it can be compared to the intertwined ecological systems on Earth.
“An active supermassive black hole is like a hungry predator dominating the ecosystem,” he said. “Simply put, it swallows up matter and influences how stars in nearby galaxies grow.”
Since they were first predicted in the early 1900s, the destructive and ominous nature of black holes has fascinated not only scientists but also the public.
Considered the most extreme objects found in the Universe, black holes contain immense mass and gravity, capable of capturing nearby matter and even light if it ventures too close.
A small subset, including the Milky Way’s central black hole, is known as “supermassive,” boasting masses millions of times, and sometimes even billions of times, that of our Sun.
Super energy emitters devour all surrounding matter
As their name implies, black holes are invisible. However, when supermassive black holes actively devour surrounding matter, they can appear as extremely bright specks in telescope images, sometimes emitting hundreds of trillions of times more energy than the Sun.
Astronomers refer to these cosmic monsters as quasars, a phase in a black hole’s life when gas and dust form a swirling disk that releases enormous energy as it spirals inward – often outshining the entire host galaxy.
Solving a long-term mystery
Early observations from the James Webb Space Telescope suggested fewer galaxies surrounding enormous quasars during the Universe’s infancy. This result was surprising, since large galaxies are commonly found in dense clusters, rather than in isolation.
Zhu stated: “We thought the JWST could be broken. Then we realised the galaxies might actually be there, but difficult to detect because their very recent star formation was suppressed.”
That realisation led to a bold new idea: Could these very bright, supermassive black holes affect not only their own galaxies but also stifle star formation in neighbouring galaxies?
Intense heat breaks down molecular hydrogen that helps stars form
To test this idea, the team studied one of the most luminous quasars ever observed: J0100+2802, which is powered by a supermassive black hole roughly 12 billion times the mass of the Sun.
The team of scientists used the JWST to measure the emissions of a specific gas, O III, an ionised form of oxygen that traces very recent star formation in galaxies. A lower ratio of O III alludes to the disruption of ideal star-forming conditions in large clouds of cold gas.
The team observed a clear distinction between galaxies within a million-light-year radius of the overpowering quasar: they showed weaker O III emission relative to their ultraviolet light, consistent with repressed, very recent star formation.
“Black holes are known to ‘eat’ a lot of stuff, but during the active eating process and in their luminous quasar form, they also emit very strong radiation,” said Zhu. “The intense heat and radiation split the molecular hydrogen that makes up vast, interstellar gas clouds, quenching its potential to accumulate and turn into new stars.”
Testing the phenomenon across multiple quasar fields
The team hopes to test whether the phenomenon is widespread across multiple quasar fields and better understand exactly how galaxies are affected by neighbouring quasars and whether other, less obvious factors are at play.
Zhu concluded: “Understanding how galaxies influenced one another in the early Universe helps us better understand how our own galaxy came to be.
“Now we realise that supermassive black holes may have played a much larger role in galaxy evolution than we once thought – acting as cosmic predators, influencing the growth of stars in nearby galaxies during the early Universe.”
