Using the James Webb Space Telescope (JWST), astronomers have discovered a supermassive black hole that appears to be incredibly large during the “cosmic dawn.” The confusion comes from the fact that it doesn’t appear that this giant void has fed on much material from its surroundings during that time—but to reach its immense size, it would have had to be voracious at the beginning of time.
The supermassive black hole that powers a quasar at the heart of the galaxy J1120+0641 was observed when the universe was only about 5% of its current age and has a mass over a billion times that of the sun.
While it is relatively easy to explain how closer and hence younger supermassive black holes grew to billions of solar masses, the merger and feeding processes that enable such growth are expected to take about a billion years. This means that searching for such supermassive black holes that existed before the 13.8 billion year old Universe was a billion years old is a real dilemma.
Since its commissioning in summer 2022, JWST has proven to be particularly efficient at discovering such challenging black holes in the cosmic dawn.
One theory about the early growth of these voids is that they were in a feeding frenzy called the “ultra-efficient feeding mode.” However, JWST’s observations of the supermassive black hole in J1120+0641 did not show a particularly efficient feeding mechanism in the material in its immediate vicinity. This finding casts doubt on the ultrafast feeding mechanism of supermassive black holes and means that scientists may know even less about the early evolution of the cosmos than they thought.
Related: How could supermassive black holes grow so large so quickly immediately after the Big Bang?
“Overall, the new observations only add to the mystery: early quasars were frighteningly normal,” said team leader and postdoctoral fellow at the Max Planck Institute for Astronomy (MPIA), Sarah Bosman, in a statement. “No matter what wavelengths we observe them at, quasars are almost identical in all epochs of the universe.”
Supermassive black holes control their own nutrition
Over the past 13.8 billion years of cosmic history, galaxies have grown in size by gaining mass either by ingesting surrounding gas and dust, by cannibalizing smaller galaxies, or by merging with larger galaxies.
About 20 years ago, before the JWST and other telescopes began detecting troubling supermassive black holes in the early universe, astronomers assumed that the supermassive black holes at the centers of galaxies were gradually growing in lockstep with the processes that lead to galactic growth.
In fact, there are limits to how fast a black hole can grow – limits that these cosmic titans set for themselves.
Due to conservation of angular momentum, matter cannot fall directly into a black hole. Instead, a flattened cloud of matter forms around the black hole, called an accretion disk. In addition, the enormous gravity of the central black hole leads to strong tidal forces that create turbulence in the accretion disk, heating it and causing it to emit light across the entire electromagnetic spectrum. These emissions are so bright that they often outshine the combined light of all the stars in the surrounding galaxy. The regions where all this happens are called quasars, and they represent some of the brightest celestial objects.
This brightness has another function. Although light has no mass, it exerts pressure. This means that the light emitted by quasars pushes on the surrounding matter. The faster the black hole that powers the quasar feeds, the greater the radiation pressure and the more likely it is that the black hole will cut off its own food supply and stop growing. The point at which black holes or other accretors starve themselves by pushing away surrounding matter is called the “Eddington limit.”
This means that supermassive black holes cannot feed and grow at any rate. Therefore, the search for supermassive black holes with masses of 10 billion suns in the early cosmos, especially less than a billion years after the Big Bang, is a real problem.
Astronomers need to know more about early quasars to determine whether early supermassive black holes could overcome the Eddington limit and become so-called “super-Eddington accretors.”
To this end, in January 2023, the team pointed JWST’s Mid-Infrared Instrument (MIRI) at the quasar at the heart of J1120+0641, located 13 billion light-years away and visible just 770 million years after the Big Bang. The survey represents the first mid-infrared study of a quasar that existed at the cosmic dawn.
The spectrum of light from this early supermassive black hole revealed the properties of the large, ring-shaped “torus” of gas and dust that orbits the accretion disk. This torus helps to channel material to the accretion disk, from where it is gradually fed into the supermassive black hole.
MIRI observations of this quasar showed that the cosmic supply chain functions similarly to that of “modern” quasars, which are closer to Earth and therefore exist in later epochs of the Universe. This is bad news for proponents of the theory that an enhanced feeding mechanism led to the rapid growth of early black holes.
In addition, measurements of the region around the supermassive black hole, where matter swirls at nearly the speed of light, agreed with observations of the same regions of modern quasars.
The JWST observations of this quasar revealed a key difference between it and its modern counterparts. The dust in the torus around the accretion disk had a temperature of about 1,130 degrees Celsius, which is about 100 degrees hotter than the dust rings around supermassive black hole-powered quasars seen closer to Earth.
The research suggests a different method of early supermassive black hole growth. It suggests that these cosmic titans had a head start in the early universe when they formed from already massive black hole “seeds.” These heavy seeds would have had a mass of at least a hundred thousand solar masses and would have been formed directly from the collapse of early and massive gas clouds.
The team’s research was published in the journal Nature Astronomy on June 17.