Galaxies are made up of various astronomical objects, including black holes, planets and stars. At the heart of a galaxy lies a supermassive black hole (SMBH), one of the most powerful and dangerous entities in the Universe.
A puzzling question for scientists is whether SMBHs gave rise to galaxies or whether galaxies formed SMBHs. Events in the early Universe may hold the key to this mystery.
The James Webb Space Telescope (JWST), launched by NASA in 2021, may be able to provide answers to this question. Using infrared technology, it captures data and images that the Hubble Space Telescope cannot capture.
A recent study published in Letters from the astrophysical journal leveraged JWST data to explore how active galactic nuclei (AGNs) in the early Universe contributed to the formation of stars and black holes.
Interesting Engineering (IE) spoke with Professor Joseph Silk, first author of the study, from John Hopkins University and the Paris Institute of Astrophysics.
Regarding their work, Professor Silk told IE: “The puzzling JWST results on distant galaxies and SMBHs were a surprise, not predicted by previous simulations of galaxy formation. »
First, let’s understand what JWST is looking for: active galactic nuclei.
SMBH and AGN
The central region around a galaxy is compact and emits a large amount of radiation of all different wavelengths across the electromagnetic spectrum. This region, known as AGN, has a high luminosity, far brighter than anything a star can produce.
Not all galaxies have AGN, but most large galaxies have SMBHs at the center. SMBHs are much more massive than ordinary black holes that can be scattered throughout a galaxy.
The relationship between AGN and SMBH is important and may answer the question of which came first: SMBH or galaxies. The AGNs are powered by the accumulation of material on SMBH.
Accretion is a phenomenon in which the gravitational attraction of the SMBH causes particles of matter (such as dust or gases) to accumulate around it, forming AGN.
AGNs are responsible for shaping the environment of their host galaxy, which ultimately shapes the formation of stars and planets. AGNs are called “active” because they constantly spew jets, flows, and intense brightness.
Since it is one of the most turbulent and dynamic phenomena in galaxies, it can help us understand the evolution of SMBHs and how they contribute to galaxy formation.
As Professor Silk explains, “SMBHs are at least ten times more common in the early universe than in our current neighborhood. Additionally, they are much more dominant relative to the mass of stars in the host galaxy than we see today. All this suggests that massive black holes formed in the early stages of galaxy formation.
Redshifted Light and the Early Universe
To study the formation of early galaxies and black holes, we need to understand the data collected by JWST.
The light that reaches us provides us with crucial information about the Universe. The farther away the origin of light is, the further back in time we observe, because it takes time for light to travel from distant objects to reach us.
Let’s look at this in more detail. As the Universe expands, light emitted in the early Universe must travel a greater distance to reach us, resulting in stretching or redshifting.
Redshifted light is light whose wavelength has shifted toward the red part of the electromagnetic spectrum, which indicates the age of the light.
The goal of JWST is to collect data on AGN in high-redshift galaxies, which are among the oldest structures in the Universe. These early structures contain information about the early Universe and the processes surrounding the formation of black holes and galaxies.
Researchers focus on ultracompact, dust-reddened galaxies, often called “little red dots.” Professor Silk explained the reason behind this nickname.
“Most of the high redshift galaxies observed by JWST have been called small red dots, red because they are dusty, and dots because they are so compact. They often contain SMBH,” he said.
Due to the presence of SMBH, these galaxies are of particular interest in determining the evolution of galaxies in the early Universe.
Using simulations and observational data from JWST, the researchers proposed a close relationship between the evolution of galaxies and SMBHs in the early Universe. This led them to define three distinct epochs based on the redshift of galaxies using the “z” parameter to explain the formation of both.
Defining eras
The redshift parameter “z” tells us how far the light from a celestial object has been stretched. Simply put, it tells us how far away a celestial object is, allowing us to travel back in time.
The first epoch: Early Universe (z > 15)
At that time, the Universe was young and galaxies were just beginning to form. These high redshift galaxies had dense star clusters, called nuclear star clusters, at their centers.
These dense stars formed a compact region near the center of the galaxy (hence the name ultra-compact high-redshift galaxies), where they eventually died, forming black holes.
“The black holes quickly merged with each other in this exceptionally dense region to form an IMBH (intermediate mass black hole) or even an SMBH. This is how the SMBH was quickly formed. Its growth was boosted by the very high central density,” said Professor Silk.
This idea is supported by the large number of these galaxies observed at high redshifts by JWST, more than those predicted by the models. Furthermore, these galaxies are a tenth or a hundredth the size of a similar galaxy mentioned by Silk today.
As black holes formed, accretion led to the formation of AGN.
The second epoch: bursts of star formation (5 < z < 15)
AGNs are now prominent and turbulent, causing gas outflows that will lead to star formation. As the black hole grows, more stars begin to form.
Professor Silk explained how gas clouds falling into SMBHs heat up due to the strong gravitational pull of the SMBH, resulting in an intense ball of energy.
He added: “Thanks to the rapid rotation (and magnetic field) of the SMBH, most of the mass falls inward to disappear into the black hole, but some is converted into a very energetic jet and flow of energy. »
“It’s this jet that crashes into nearby orbiting gas clouds, overwhelming them, and its enormous pressure compresses them. The clouds collapse and fragment into stars. »
The third epoch: Tempering (z < 5)
As the Universe moves to lower redshifts, it has expanded further. Winds near AGN cause the dispersion of gases necessary for star formation.
If the gas reservoir is depleted, star formation will also be stopped, causing star formation rates to decline over time within a galaxy.
Synergy, co-evolution and the future of JWST
There appears to be a close relationship between the evolution of SMBHs and their host galaxies, which relies on the synergistic relationship between AGN activity and star activity.
This means that AGN activity, driven by the accretion of material onto SMBHs, affects star formation by releasing large amounts of energy. Conversely, star growth can affect SMBHs by causing a loss of stellar mass, which can contribute to the formation of the accretion disk.
This bimodal or dual synergy tells us that the co-evolution of SMBHs and their galactic hosts is complex. Studying AGN can provide more insight into these complex processes, which is why the data collected by JWST is so important.
Regarding future JWST measurements, Professor Silk said: “New observations will be available from JWST next year. These will provide improved spectroscopy. This will allow us to measure the masses of SMBHs and stars more precisely, particularly at the centers of galaxies that host SMBHs.
However, he also highlighted the lack of high-resolution simulations needed to fully understand the phenomena of cloud crushing (gas clouds) and star formation.
Therefore, the question of whether SMBHs or galaxies formed first remains unanswered.
ABOUT THE PUBLISHER
Tejasri Gururaj Tejasri is a versatile science writer and communicator, leveraging her expertise from a master’s degree in physics to make science accessible to everyone. In her free time, she enjoys spending quality time with her cats, watching TV shows, and recharging with naps.