Galaxies consist of various astronomical objects, including black holes, planets and stars. At the core 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 was whether SMBHs produced galaxies or whether galaxies formed SMBHs. Events in the early universe could hold the key to this mystery.
The James Webb Space Telescope (JWST), launched by NASA in 2021, may be able to answer this question. Using infrared technology, it captures data and images that the Hubble Space Telescope cannot.
A recent study published in The astrophysical diary letters used data from the JWST to investigate how active galactic nuclei (AGN) in the early universe contributed to the formation of stars and black holes.
Interesting technology (IE) spoke to Prof. Joseph Silk, the study’s first author, from John Hopkins University and the Paris Institute of Astrophysics.
Speaking about their work, Prof. Silk told IE: “JWST’s puzzling results on distant galaxies and SMBHs were a surprise, not predicted by previous simulations of galaxy formation.”
Let’s first 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 brightness, much brighter than anything a star can produce.
Not all galaxies have AGN, but most large galaxies have SMBHs in the center. SMBHs are much more massive than regular black holes that can be found scattered throughout a galaxy.
The relationship between AGN and SMBH is important and may answer the question of which came first: SMBH or galaxies. AGNs are powered by the accretion of material on SMBH.
Accretion is a phenomenon in which the gravity of the SMBH causes matter particles (such as dust or gases) to accumulate around it, forming the AGN.
AGNs are responsible for shaping the environment of their host galaxy, which ultimately determines the formation of stars and planets. AGNs are called ‘active’ because they continuously radiate, radiate, and radiate intense brightness.
Because it is one of the more turbulent and dynamic phenomena in galaxies, it can help us understand the evolution of SMBH and how they contribute to galaxy formation.
As Prof. Silk explained: “SMBHs are at least ten times more common in the early universe than in our current environment. Furthermore, they are much more dominant to the mass of the stars in the host galaxy compared to what we see today. All this indicates that massive black holes formed at the earliest stages of galaxy formation.”
Red-shifted light and the early universe
To study the early formation of galaxies and black holes, we need to understand the data collected by JWST.
Light traveling toward us carries crucial information about the universe. The further 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 dig into this further. As the universe expands, the light emitted in the early universe must travel a greater distance to reach us, which results in the light being stretched, or red-shifted.
Red-shifted light is light whose wavelength has been shifted toward the red portion of the electromagnetic spectrum, which is indicative of the age of the light.
The focus of JWST is to collect data on AGN at high-redshift galaxies, some of 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.
The researchers focus on ultra-compact galaxies reddened by dust, also known as ‘little red dots’. Professor Silk explained the reasoning behind this nickname.
“Most of the high-redshift galaxies observed by JWST are called small red dots: red because they are dusty, and dots because they are so compact. They often contain SMBHs,” he said.
Because of the presence of SMBHs, these galaxies are of particular importance in determining the evolution of galaxies in the early Universe.
Using simulations and the observational data from JWST, the researchers proposed a close relationship between galaxy evolution and SMBHs in the early Universe. This led them to define three different epochs based on the redshift of galaxies, using the parameter “z” to explain the formation of both.
Defining eras
The redshift parameter “z” tells us how much the light from a celestial body is stretched. In simple terms, it tells us how far away a celestial body is, effectively allowing us to look back in time.
The first era: the early universe (z > 15)
During this time, the universe was young and galaxies were just beginning to form. These highly redshifted galaxies had dense clusters of stars at their centers, called nuclear star clusters.
These dense stars formed a compact region near the center of the galaxy (hence the name ultracompact high-redshift galaxies), where they eventually died out and formed 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. Thus, the SMBH quickly emerged. Growth was boosted by the really high central density,” said Prof. Silk.
This idea is supported by the large number of such galaxies observed by JWST at high redshifts, more than what is predicted by models. Furthermore, these galaxies are one-tenth or one-hundredth the size of a similar galaxy known today as Silk.
When black holes formed, accretion led to the formation of AGN.
The second epoch: bursts of star formation (5 < z < 15)
AGN is now prominent and turbulent, leading to the outflow of gases that will lead to star formation. The larger the black hole becomes, the more stars will form.
Prof. Silk explained how gas clouds falling into SMBHs heat up due to the SMBH’s strong gravity, resulting in an intense ball of energy.
He went on to say, “Thanks to the SMBH’s fast rotation (and magnetic field), most of the mass falls in to disappear into the black hole, but some is converted into a very energetic jet and an outflow of energy.”
“It is this jet that crashes into nearby gas clouds in orbit, overwhelming them, and the enormous pressure compresses them. The clouds collapse and disintegrate into stars.”
The third age: the extinction (z < 5)
As the universe transitions to lower redshifts, it has expanded further. The winds near AGN spread the gases needed for star formation.
As the gas reservoir becomes depleted, star formation will also be extinguished, leading to lower star formation rates within a galaxy over time.
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 stellar activity.
This means that AGN activity, driven by the accretion of matter on SMBHs, influences star formation by releasing large amounts of energy. Conversely, stellar growth can affect SMBHs by causing a loss of stellar mass, which can contribute to the accretion disk.
This bimodal or double synergy tells us that the coevolution of SMBHs and their galactic hosts is complex. AGN’s research can provide more insight into these complex processes. That’s why the data collected by JWST is so important.
Regarding future measurements of JWST, Prof. Silk said: “New observations of JWST will be available next year. These will provide improved spectroscopy. This will allow us to more accurately measure the masses of the SMBH and stars, especially in the centers of the galaxies in which the SMBHs occur.”
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 unresolved.
ABOUT THE EDITORIAL
Tejasri Gururaj Tejasri is a versatile science writer & Communicator, who uses her expertise from an MS in Physics to make science accessible to everyone. In her free time, she enjoys spending quality time with her cats, enjoying TV shows and rejuvenating through naps.
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