Astronomers say we may be living at the center of a cosmic void 2 billion light-years wide that defies the laws of cosmology

Our home galaxy, the Milky Way, is just one of billions in our universe. So in the grand scheme of things, we’re not that special. But zoom into our local cosmic neighborhood and that story begins to change.

A growing list of observations suggests that we live in the crosshairs of a gigantic cosmic void – the largest ever observed. Astronomers first suggested such a void in 2013, and evidence for its existence has been mounting ever since.

But the nice thing is that this gigantic void should not exist in the first place. If it exists, it means there is probably something wrong with our understanding of the cosmos.

We may be living in a void that shouldn’t exist


A map of our local universe, in an oval shape.

A map of our local universe.

Harvard-Smithsonian Center for Astrophysics



According to a fundamental theory of cosmology called the cosmological principle, matter in the universe should be uniformly distributed on a very large scale.

The reason this matters is that by assuming uniformity, scientists can apply the same laws of physics to nearby objects as they did to objects at the edge of the early universe. In other words, everything functions under the same universal laws.

It’s a simple, straightforward approach to studying and understanding our universe, and it suggests that voids – like the one we live in – shouldn’t exist.

But several observations over the past decade suggest that matter in the universe can clump together in regions of high and low densities, meaning it may not be so uniform after all.


A map of a portion of the universe showing areas of high and low density.

The Dark Energy Spectroscopic Instrument created the largest 3D map of our universe to date. This slice of the cosmos shows the areas of high and low density.

Collaboration Claire Lamman/DESI; custom color chart package by cmastro



“It is now quite clear that we are in significant underdensity,” Indranil Banik, a postdoctoral researcher at the University of St. Andrews, told Business Insider.

“There are a few people who are still against it to a limited extent. For example, some people have rightly argued that such a void should not exist in the Standard Model, which is true. Unfortunately, that doesn’t prove that it isn’t there. ,” he added.

Banik co-authored a paper published late last year in the peer-reviewed journal Monthly Notices of the Royal Astronomical Society that suggests we may be living near the center of this void – the so-called KBC void – which is about 2 billion light years wide. Wide enough to accommodate 20,000 Galaxies in a row stretching from one end to the other.

The emptiness of the KBC defies the laws of cosmology


The Hubble Telescope above Earth

Observations from the Hubble Telescope conflict with standard cosmological predictions about the expansion of the universe. The void at KBC could explain why.

NASA



KBC’s emptiness is not completely empty. That cannot be the case, because we live in it. But if Banik and his colleagues’ calculations are correct, the void would be about 20% emptier than the space outside the boundary.

That may not seem like a big deficit, but according to the recent study, it’s enough to cause confusing behavior in our local cosmic environment.

In particular, nearby stars and galaxies are moving away from us faster than they should. Cosmologists have a value called the Hubble constant that they use to help describe how quickly the expansion of the universe is accelerating.

The Hubble constant must have the same value everywhere, whether it is close or very far away. The problem is that the galaxies and stars in our local neighborhood appear to be moving away from us faster than Hubble’s constant predicts, essentially violating our law of cosmology that describes how the universe grows and evolves.


andromeda galaxy

At about 2.5 million light-years away, the Andromeda Galaxy is the closest major galaxy to the Milky Way.

NASA/JPL-Caltech



Astronomers cannot agree on the cause of this discrepancy in the Hubble constant, and this claim has become known as the Hubble tension.

Banik and his colleagues suggest that the void could be a solution, because regions of high density and stronger gravity outside the void could pull galaxies and stars toward them.

Banik argues that this outflow could explain why cosmologists have calculated a higher value for the Hubble constant when looking at nearby objects. Things move faster in the void and fly out of our empty area into the crowded space.

Mystery solved? Not yet.


A photo of the cosmos with a zoomed-in portion.

The void at KBC is not the only possible solution to the Hubble tension. Some scientists are peeling back layers of the cosmos in search of early dark energy.

NASA/ESA/A. Riess (STScI/JHU)/Palomar digitalized aerial survey



If the void does indeed exist, as the evidence suggests, that may mean revising some of the laws of physics we use to describe the cosmos. After all, Banik’s theory would explain why Hubble’s constant is higher in our local cosmic region.

“The hypothesis that a local void could explain the Hubble strain by causing a significant outflow seems correct in principle, especially given the supporting observational data cited in the study,” said Brian Keating, a cosmologist and professor of physics at the University of California San Diego, which has the Hubble constant, told BI in an email.

But there are still questions that need to be answered. First, how far does the void’s influence extend?

“If the local void is not representative of the broader cosmos, this can only provide a local solution, not a global solution – that would not ‘resolve’ the Hubble tension,” Keating wrote.

Keating also noted that Banik’s theory had certain limitations, and wrote that the results of the study depended on the type of void model used. Different models yield different predictions about void effects and the ‘bulk flow’, or the average speed of galaxies as they move through the cosmos. Furthermore, models can only provide a simplified view of what the void actually is.

All this means the void could be offer a solution, but “it is not yet definitive ‘proof’ of the resolution of the tension,” Keating wrote.

There are also other solutions to consider, such as early dark energy. This theory proposes a new form of energy that influences the universe’s expansion rate early on, ultimately leading to the Hubble tension we observe today, as Keating said.


A star shines against a starry sky.

Methuselah, the oldest star ever observed. Scientists disagree on exactly how old this star is, and some studies suggest it could somehow be older than the universe itself.

Digitized Sky Survey (DSS)/STScI/AURA/Palomar/Caltech/UKSTU/AAO



But Banik noted that the early dark energy theory conflicted with certain truths about the universe. For example, we would have to adjust the ages of old stars to make it work. Otherwise, these stars would have to be older than the universe itself, Banik said.

So he sticks to his theory of emptiness. His next research project aims to analyze supernova data to find out whether Hubble’s constant returns to the value predicted by our standard model of cosmology beyond the void. If his theory is correct, there should be no Hubble tension outside the boundaries of the void.

“This is the main thing that keeps me a little awake sometimes: I worry whether the supernovae really show that we are in a universe that is actually expanding faster, and that there is no sign of the edge of the void,” said Bankik.

Until then, the Hubble tension remains a mystery waiting to be solved.

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