We misunderstand the universe due to a vast void spanning 1 billion light-years, which is where we exist.

Scientists believe that the observed discrepancy in the expansion rate of the Universe (the Hubble constant), known as the Hubble problem, arises because Earth is located in a vast void, a region of space with low density. The Hubble problem stems from the existence of two methods for calculating the Hubble constant, which do not align with one another. Additionally, astronomers have made another significant discovery indicating that the primary cosmological model of the Universe's evolution needs to be reevaluated. This research has been published in the Monthly Notices of the Royal Astronomical Society, reports Space.

KBC Supervoid

Our galaxy, the Milky Way, along with the Solar System and Earth, resides in a region of space with lower density, known as the KBC supervoid.

In space, there are voids (which do not exceed 300 million light-years in width) and supervoids, where the density of matter is below the average for the Universe. In the KBC supervoid, matter is approximately 20% less dense than the average density in space, and the width of this void is estimated to be 1 billion light-years. The largest void in the Universe is the Eridanus supervoid, which spans 1.8 billion light-years.

The Universe is continuously expanding, but astronomers cannot accurately determine the exact rate of this expansion, i.e., the value of the Hubble constant. Without this, scientists cannot fully understand the development of the cosmos. The Hubble problem suggests that something is missing in the best model of the Universe's evolution, known as the Lambda-CDM model.

According to scientists, when measuring the Hubble constant, astronomers do not look too far into the Universe and limit their observations to a distance of 2 billion light-years. This means that the measurements of the Hubble constant reflect the expansion rate of the Universe within the KBC supervoid.

What is the Hubble Problem?

There are two methods for calculating the expansion rate of the Universe, which can be termed theoretical and observational. In the first method, astronomers observe the cosmic microwave background radiation, the first light that traversed space. This nearly uniform and homogeneous radiation fills the entire Universe. Using the Lambda-CDM model as a template, astronomers "rewind" time and simulate the evolution of the cosmos based on this radiation. This allows them to obtain the value of the Hubble constant or the rate of cosmic expansion.

In the observational method, astronomers measure how quickly galaxies are receding from us by studying the change in their light wavelengths or redshift. The longer light travels through space, the more it shifts toward the red part of the spectrum. Thus, the farther an object is, the higher the redshift. A high redshift also indicates how quickly a galaxy is moving away, allowing for the calculation of the Hubble constant.

The issue is that the observational method yields a higher value for the Hubble constant than the theoretical method based on the Lambda-CDM model. If the measurement of the cosmic microwave background radiation indicates that the Universe is expanding at a rate of 68 km/s per megaparsec, the second method shows a rate between 70 and 76 km/s per megaparsec.

One parsec is equal to 3.26 light-years. Accordingly, one megaparsec is 3.26 million light-years. One light-year equals 9.4 trillion kilometers. The authors of the study suggest that, based on the discrepancies in the obtained data, it can be concluded that the best cosmological model, namely the Lambda-CDM model, is incorrect.

How does the KBC supervoid contribute to the Hubble problem?

Astronomers believe that the Hubble problem arises because the Universe is expanding faster within the KBC supervoid. This is a homogeneous section of space that possesses some negative mass. This leads to a repulsive gravitational effect, which may amplify the redshifts of galaxies.

Scientists state that the theoretical method averages the Hubble constant across the entire Universe, while the observational method measures it only within the KBC supervoid. Thus, the understanding of the entire Universe is distorted from within this void.

In other words, the authors of the study argue that the Universe appears to be expanding faster than it actually is. This could be a potential solution to the Hubble problem.

A discovery that contradicts the standard cosmological model of the Universe

In fact, the authors of the study aimed to determine how well the existing supervoids align with the standard cosmological model, namely the Lambda-CDM model. They were not initially focused on the Hubble problem but nevertheless recognized its potential solution.

Astronomers found that such vast voids in space, like the KBC supervoid, cannot exist within the Lambda-CDM model, at least in its current form. This implies that this model of the Universe's evolution needs to be reevaluated, according to the scientists.