JWST sees the beginning of the cosmic web

The cosmic web is the large-scale structure of the universe. If you could watch our universe unfold from the Big Bang to today, you would see these filaments (and the voids between them) form over time. Now, astronomers using the JWST have found ten galaxies that form a very early version of this structure just 830 million years after the beginning of the universe.

The “cosmic web” began as fluctuations in density in the early universe. A few hundred million years after the Big Bang, matter (in the form of primordial gas) condensed into knots at the junctions of plates and gas filaments in the early lattice. These knots and filaments hosted the first stars and galaxies. Naturally, as astronomers look back in time, they will be looking for early versions of the cosmic web. JWST technology allowed them to look back at the dim, opaque things that were around shortly after the Big Bang.

The 10 galaxies the team observed line up in a thin filament three million light-years across held together by a bright quasar. Its appearance surprised the team with its size and place in cosmic history. “This is one of the oldest filamentous structures people have found associated with a distant quasar,” added Vig Wang of the University of Arizona in Tucson, the principal investigator on this program.

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Aspire to understand the early universe and the cosmic web

The JWST observations are part of a monitoring program called ASPIRE: A Spectroscopy Survey of Bias Halos in the Reionization Era. It uses images and spectra of 25 quasars that existed in the past when the universe began to lighten after the “dark ages”. The idea is to study the formation of the closest possible 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 it all happened during the era of reionization.

This is an artist's illustration showing the early universe timeline showing some of the major time periods. On the left is the universe's first day, as intense heat prevented much from happening. The CMB is then released once the universe has cooled down a bit. Next, in yellow, is the neutral universe, the time before star formation. The hydrogen atoms in the neutral universe should be emitting radio waves that we can detect here on Earth. Image credit: ESA - C. Carreau — This is an artist’s illustration showing the early universe timeline showing some of the major time periods. On the left is the universe’s first day, as intense heat prevented much from happening. The CMB is then released once the universe has cooled down a bit. Next, in yellow, is the neutral universe, the time before star formation. The hydrogen atoms in the neutral universe should be emitting radio waves that we can detect here on Earth. Image credit: ESA – C. Carreau

ASPIRE goals are an important part of understanding the origin and evolution of the universe. “The last two decades of cosmology research have given us a solid understanding of how the cosmic web formed and evolved. ASPIRE aims to understand how the emergence of the oldest massive black holes can be incorporated into our current story of cosmological structure formation,” explained team member Joseph Henawi of the University of California, Santa Barbara.

Focus on early black holes

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

Artist’s impression of a quasar. At least one is involved in early threads in 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 mass of these black holes ranges from 600 million to 2 billion times the mass of the sun. This is really very huge and raises a lot of questions about their rapid growth. For these supermassive black holes to form in such a short time, two criteria must be met. First, you need to start growing from a supermassive black hole “seed”. Secondly, even if this seed started with a mass equivalent to a thousand suns, it still needed to accumulate a million times more matter at the maximum possible rate throughout its lifetime,” Wang explained.

In order for these black holes to grow as they did, they needed a lot of fuel. Their galaxies were also very massive, which could explain the monstrous black holes in their cores. Not only did those black holes suck in a lot of material, but their outflows also affected star formation. Strong winds from black holes can prevent star formation in the host galaxy. Such winds have been observed in the nearby universe but not directly observed in the era of reionization,” Yang said. “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 the age?

We often hear about astronomers wanting to go back to the age of reionization. Why is such a puzzling goal? It offers a look at a time when the first stars and galaxies formed. After the Big Bang, the infant universe was in a hot, dense state. We sometimes hear it referred to as the primordial universe soup. After that, expansion took over and things started to cool down. This allowed electrons and protons to combine to form the first neutral gas atoms. It also allowed the spread of thermal energy from the Big Bang. Astronomers detect this radiation. It is redshifted in the microwave portion of the electromagnetic spectrum. Astronomers call it 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 transformational epoch: the reionization epoch. Credit: Paul Gill and Simon Mach/University of Melbourne

This side of the early universe had slight density fluctuations in its expanding matter. That substance was neutral hydrogen. There were no stars or galaxies yet. But, eventually, these high-density regions began to clump together under the influence of gravity, causing the neutral matter to begin to clump together as well. This led to further collapse of the high-density regions, which eventually led to the birth of the first stars. They heated the surrounding material, which poked holes in the neutral zones – allowing light to pass through. Essentially, those holes (or bubbles) in the neutral gas allowed ionizing radiation to travel farther through space. It was the beginning of the era of reionization. A billion years after the Big Bang, the universe was completely ionized.

So, how do you explain early supermassive black holes?

Interestingly, those early galaxies that JWST found, along with their quasars, were already all in place, with supermassive black holes at their cores. The main question remains: How did they get so big so quickly? Their presence may tell astronomers something about “extra densities” in the infant universe. First, the “seed” of a black hole needs a dense region full of galaxies in order to form.

However, so far, observations prior to JWST’s discovery have found only a few increased galaxy densities around the oldest supermassive black holes. Astronomers need to make more observations in this era to explain why. The ASPIRE program should help resolve questions about the feedback between galaxy formation and black hole creation in this very early era of the universe. Along the way, they should also see more fragments of the large-scale structure of the cosmic web of the universe as it takes shape.