As we explore the vastness of the cosmos, we discover a myriad of galaxies twinkling like stars in the darkness. However, the distribution of these galaxies is not random; they tend to cluster together, forming filaments and clusters within the cosmic web. Conversely, there are regions of much lower density called voids, where only a few galaxies reside. One such void is the Local Void, in which our Milky Way galaxy is situated. But the Local Void may be part of a larger underdensity called the Local Hole or Keenan-Barger-Cowie (KBC) supervoid. This poses a significant challenge to the standard model of cosmology, as it cannot explain such an enormous underdensity.
Measurement of the rate at which the Universe is expanding, known as the Hubble Constant or H0, has presented a conundrum. Different methods of measuring this constant yield disparate results. One approach involves studying remnants of the early Universe, such as the cosmic microwave background or frozen acoustic waves, which gives a rate of approximately 67 kilometers per second per megaparsec. Another method involves measuring the distances to nearby objects with known brightness, resulting in a rate of around 73 kilometers per second per megaparsec.
A recent study led by astrophysicist Sergij Mazurenko suggests that considering the Local Hole could offer a solution to the Hubble Tension. Matter exerts gravitational attraction on other matter, which means galaxies moving away from us in local space might experience local acceleration due to the concentrations of matter surrounding the edges of the supervoid. This concept resembles a previous study on the Local Void’s impact on the expansion rate, but on a much grander scale.
The main obstacle lies in the standard model of cosmology, which struggles to incorporate the Local Hole. However, an alternative model called Modified Newtonian Dynamics (MOND) could address this issue. MOND was proposed as an explanation for gravity discrepancies in our measurements and provides a different interpretation of how gravity works compared to Einstein’s theory. By adopting MOND, resolving the Local Hole becomes more feasible.
While MOND offers potential solutions, it has its own limitations and challenges. Yet, it serves as a valuable tool to expand our understanding of the Universe and identify gaps in our current theories. Perhaps the true answer lies in a combination of both the standard model and MOND, as a way to build upon Einstein’s theories rather than completely discarding them. Physicist Indranil Banik from St Andrews University highlights Einstein’s belief that we cannot solve problems using the same thinking that led to the problems in the first place.
The vastness of the cosmos holds many mysteries, and the Local Hole within the Local Void adds another layer of complexity. By considering this underdensity and exploring alternative models such as MOND, we may find a path towards resolving the enigma of the Hubble Tension. The journey towards understanding the nature of our Universe requires embracing new ideas and expanding our existing theories. Only through such endeavors can we hope to uncover the true workings of the cosmic tapestry that stretches beyond our Milky Way.