The cosmic web is a large-scale structure of the universe. If you could watch our universe extend from the Big Bang to the present day, you would see these filaments (and the gaps between them) forming over time. Now, astronomers using JWST have discovered ten galaxies that formed the earliest version of this structure just 830 million years after the beginning of the universe.
The “cosmic web” began as density fluctuations in the early universe. Several hundred million years after the Big Bang, matter (in primordial gaseous form) condensed into knots at the junctions of plates and gas filaments in the early lattice. These knots and filaments housed the first stars and galaxies. Naturally, when astronomers look to the past, they will be looking for an early version of the cosmic web. JWST’s technology allowed them to see again the dim and blurry objects that were around shortly after the Big Bang.
The 10 galaxies the team observed are lined up in thin filaments three million light years long that are held together by bright quasars. His appearance shocked the team with its size and place in cosmic history. “This is one of the oldest filamentary structures that people have found associated with distant quasars,” added Vig Wang of the University of Arizona at Tucson, the program’s principal investigator.
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Aspiring to understand the early universe and cosmic networks
The JWST observations are part of a monitoring program called ASPIRE: Halos Bias Spectroscopy Surveys in the Reionization Era. It uses images and spectra from 25 quasars that existed in the distant past when the universe began to brighten after the “Dark Ages”. The idea is to study the formation of nearby galaxies, as well as the birth of the first black holes. In addition, the team hopes to understand how the early universe was enriched with heavier elements (metals), and how this happened during the reionization era.
This is an artist’s illustration showing a timeline of the early universe showing some of the major time periods. On the left is the first day of the universe, as intense heat prevented much from happening. CMB was then released after the universe cooled slightly. Next up, in yellow, is the neutral universe, the time before star formation. Hydrogen atoms in the neutral universe should emit radio waves that we can detect here on Earth. Image credit: ESA – C. Carreau
ASPIRE’s goals are an important part of understanding the origin and evolution of the universe. “Cosmological research over the past two decades has provided us with a solid understanding of how cosmic networks form and evolve. ASPIRE aims to understand how the emergence of the oldest massive black holes can fit into the story of the formation of our current cosmological structure,” explained team member Joseph Henawi of the University of California, Santa Barbara.
Focus on the initial black hole
Quasars mesmerize through space and time. They are powered by supermassive black holes which, together with powerful jets, produce incredible amounts of light and other emissions. Astronomers use it as a standard candle for measuring distances, as well as a way to study the large regions of space through which light travels.
Artist’s impression of the quasar. At least one is involved in the initial threads on the cosmic web. Credit: NOIRLab/NSF/AURA/J.da Silva
At least eight of the quasars in the Aspire study have black holes that formed less than a billion years after the Big Bang. The masses of these black holes range from 600 million to 2 billion times the mass of the sun. It is huge and raises many questions about their rapid growth. In order for this supermassive black hole to form in such a short time, two criteria must be met. First, you must start growing from the “seed” of a supermassive black hole. Second, even if this seed were to start with the mass equivalent of a thousand suns, it would still need to accumulate a million times more matter at the maximum possible rate throughout its lifetime,” explained Wang.
For these black holes to grow like that, they need a lot of fuel. Their galaxy is also very massive, which could explain the monstrous black hole at its core. The black hole not only sucks in a lot of material, but the outflow also influences star formation. Strong winds from black holes can prevent star formation in host galaxies. Such winds have been observed in the nearby universe but not directly observed in the reionization era,” said Yang. “The size of the wind is related to the structure of the quasar. In Webb’s observations, we see that such winds existed in the early universe.”
Why age?
We often hear about astronomers wanting to return to the age of reionization. Why confusing goals? It offers a look at the time when the first stars and galaxies formed. After the Big Bang, the baby universe was in a hot, dense state. We sometimes hear it referred to as the soup of the primordial universe. After that, expansion took over and things started to cool off. This allowed electrons and protons to combine to form the first neutral gas atoms. It also allows for the dispersion of the heat energy from the Big Bang. Astronomers detect this radiation. It is red shifted in the microwave portion of the electromagnetic spectrum. Astronomers call this cosmic microwave background radiation (CMB).
A visualization of what the universe may look like as it goes through its last great epoch of transformation: the epoch of reionization. Credits: Paul Gill and Simon Mach/University of Melbourne
This side of the early universe had very few density fluctuations in expanding matter. That substance is neutral hydrogen. There are no stars or galaxies yet. But, eventually, these areas of high density start to agglomerate under the influence of gravity, causing neutral matter to start clumping together. This led to the further collapse of the high-density regions, which eventually led to the birth of the first stars. They heat the surrounding material, which creates a hole in the neutral zone – allowing light to pass through. Basically, holes (or bubbles) in a neutral gas allow ionizing radiation to travel farther through space. It was the beginning of the reionization era. One billion years after the Big Bang, the universe is completely ionized.
So how do you explain the early supermassive black holes?
Interestingly, the early galaxies that JWST discovered, along with their quasars, were all already present, with supermassive black holes at their cores. The main question remains: How did they get so big so fast? Their presence might tell astronomers something about the “extra density” in the baby universe. First, a “seed” black hole requires a dense region full of galaxies to form.
So far, however, observations prior to the JWST discovery have found only a modest increase in the density of galaxies around the oldest supermassive black holes. Astronomers will need to make more observations in this era to explain why. The ASPIRE program should help answer questions about the feedback between galaxy formation and the creation of black holes in this early universe. Along the way, they also got to see more and more fragments of the large-scale structure of the cosmic web of the universe as it formed.
for more information
NASA Web identifies the first strands of the cosmic web
Halos Bias in the Reionization Era (ASPIRE) Spectroscopic Survey: JWST reveals a filamentous structure around az=6.61 Quasar
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2023-07-03 03:04:18
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