JWST sees the beginning of the cosmic web

The Cosmic Web is the large-scale structure of the universe. If you can watch our universe unfold from the Big Bang to today, you can see these filaments (and the voids between them) forming throughout time. Now, astronomers using JWST have identified ten galaxies that form an early version of this structure just 830 million years after the universe began.

The „cosmic web” began as density fluctuations in the early universe. A few hundred million years after the Big Bang, material (in primordial gaseous form) condensed into nodules at the intersections of sheets and filaments of gas in the early web. These knots and filaments provided the first stars and galaxies. When astronomers look back in time, it’s only natural that they look for early versions of the cosmic web. JWST allowed them to look back at the faintest, faintest objects since the Big Bang.

The ten galaxies the team found are aligned in a thin, three-million-light-year-long thread anchored by a bright quasar. Its appearance surprised the team both for its size and its place in cosmic history. „This is one of the earliest filamentary structures people have found associated with a distant quasar,” said Feige Wang of the University of Arizona in Tucson, the project’s principal investigator.

Aspiring to understand the early universe and the cosmic web

The JWST observations are part of an observational project called ASPIRE: Spectroscopic Survey of the Dependent Halo in the Reionization Era. It uses both images and spectra of 25 quasars from when the universe began to glow after the „dark ages.” The idea is to study the formation of the earliest possible galaxies and the births of the first black holes. In addition, the team hopes to understand how the early universe was enriched with heavy elements (metals) and how it behaved during the recrystallization epoch.

This is an artist's illustration of a timeline of the early universe showing some key periods.  On the left is the early day of the universe, where intense heat prevented anything from happening.  After that the CMP release as the universe cools down a bit.  Then, in yellow, is the Neutral Universe, the time before stars formed.  Hydrogen atoms in the neutral universe must have given off the radio waves we can detect on Earth.  Image credit: ESA – C. Carreau
This is an artist’s illustration of a timeline of the early universe showing some key periods. On the left is the early day of the universe, where intense heat prevented anything from happening. After that the CMP release as the universe cools down a bit. Then, in yellow, is the Neutral Universe, the time before stars formed. Hydrogen atoms in the neutral universe must have given off the radio waves we can detect on Earth. Image credit: ESA – C. Carreau

ASPIRE targets are an important part of understanding the origin and evolution of the universe. „The last two decades of cosmological research have given us a strong understanding of how the cosmic web forms and evolves. ASPIRE aims to understand how to connect the origin of early supermassive black holes to our current story of cosmic system formation,” said team member Joseph Hennavi of the University of California, Santa Barbara. explained.

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Focus on early black holes

Quasars call across time and space. They are powered by supermassive black holes that produce incredible amounts of light and other emissions with powerful jets. Astronomers use them as standard candles for distance measurements and as a way to survey the vast regions of space through which their light passes.

Artist’s impression of a quasar. At least one is implicated in an initial strand in the cosmic web. Credit: NOIRLab/NSF/AURA/J. Da Silva

The ASPIRE study found black holes in at least eight quasars that formed within a billion years of the Big Bang. These black holes have 600 million to 2 billion times the mass of the Sun. It is actually very large and raises a lot of questions about their rapid growth. „To create these supermassive black holes in such a short period of time, two criteria must be met. First, you have to start from a massive 'seed’ black hole. Second, even if this seed starts out with a mass equal to a thousand suns, it will still grow at a million times the maximum possible rate over its entire lifetime. to accumulate material,” Wang explained.

For these black holes to grow, they needed a lot of fuel. Their galaxies were also very massive, which could explain the supermassive black holes at their hearts. Not only do those black holes suck up a lot of material, but their ejection also affects star formation. „Strong winds from black holes can suppress star formation in the host galaxy. Such winds have been observed in the nearby universe, but they have not been observed directly in the reorganization epoch,” Yang said. „The amount of wind is related to the structure of the quasar. In the Webb observations, we see that such a wind existed in the early universe.

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Why Era?

We often hear of astronomers who wish to look back to the era of reionization. Why is this such a cruel goal? It gives the time when the first stars and galaxies formed. After the Big Bang, the baby universe was in a hotter, denser state. Sometimes we hear it referred to as the primordial soup of the universe. Then, expansion took off and things started to cool down. This allowed electrons and protons to combine to form the first neutral atoms of a gas. This allowed the heat energy from the Big Bang to dissipate. Astronomers have detected that radiation. It is red-shifted to the microwave region of the electromagnetic spectrum. Astronomers call this the „cosmic microwave background” radiation (CMB).

The first stars
A visualization of what the universe looked like when it was going through its last major transformative epoch: the epoch of reionization. Credit: Paul Gale & Simon Mutch/University of Melbourne

This aspect of the early universe had small fluctuations of density in its expanding material. That substance is neutral hydrogen. No stars or galaxies yet. But, eventually, these highly dense regions began to merge under gravity, causing neutral matter to accumulate as well. This led to further collapse of the denser regions, which eventually led to the birth of the first stars. They heated up the surrounding material, which punched holes in neutral areas—and this allowed light to travel through. Essentially, holes (or bubbles) in the neutral gas allowed ionizing radiation to travel great distances into space. This was the beginning of the era of reionization. A billion years after the Big Bang, the universe was completely ionized.

So, how do we explain the early supermassive black holes?

It is interesting that those early galaxies discovered by JWST, with their quasars, were already fully in place, with supermassive black holes at their centers. That key question remains: How did they grow so fast? Their presence may tell astronomers something about the „overdensity” in the baby universe. First, the formation of a black hole „seed” requires a highly dense region filled with galaxies.

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However, so far, observations prior to the JWST discovery have detected only a few interstellar overdensities around early supermassive black holes. Astronomers will need to make more observations during this era to explain why. The ASPIRE project will help address questions about the feedback between star formation and black hole formation in this early epoch of the universe. Along the way, many pieces of the larger-scale structure of the cosmic web of the universe should be seen as they form.

For more information

NASA’s web identifies the earliest strands of the cosmic web
A spectroscopic survey of biased haloes in the reionization epoch (ASPIRE): JWST az = 6.61 reveals a filamentary system around the quasar.

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