The KBC Void (or Local Hole) is an immense, comparatively empty region of space, named after astronomers Ryan Keenan, Amy Barger, and Lennox Cowie, who studied it in 2013. [1] The existence of a local underdensity has been the subject of many pieces of literature and research articles. [2] [3] [4]
The underdensity is proposed to be roughly spherical, approximately 2 billion light-years (600 megaparsecs, Mpc) in diameter. As with other voids, it is not completely empty but contains the Milky Way, the Local Group, and the larger part of the Laniakea Supercluster. The Milky Way is within a few hundred million light-years of the void's center. [5]
It is debated whether the existence of the KBC void is consistent with the ΛCDM model. While Haslbauer et al. say that voids as large as the KBC void are inconsistent with ΛCDM, [6] Sahlén et al. argue that the existence of supervoids such as the KBC void is consistent with ΛCDM. [7] Galaxies inside a void experience a gravitational pull from outside the void, which yields a larger local value for the Hubble constant, a cosmological measure of how fast the universe expands. Some authors have proposed the structure as the cause of the discrepancy between measurements of the Hubble constant using galactic supernovae and Cepheid variables (72–75 km/s/Mpc) and from the cosmic microwave background and baryon acoustic oscillation data (67–68 km/s/Mpc). [8]
Other work has found no evidence for this in observations, finding the scale of the claimed underdensity to be incompatible with observations which extend beyond its radius. [9] Important deficiencies were subsequently pointed out in this analysis, leaving open the possibility that the Hubble tension is indeed caused by outflow from the KBC void, albeit in the context of MOND gravity rather than general relativity. [6] It was later discovered that this outflow model successfully predicted the bulk flow curve, an important measure of the velocity field in the local Universe. [10]
The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby galaxies. Galaxy formation is hypothesized to occur from structure formation theories, as a result of tiny quantum fluctuations in the aftermath of the Big Bang. The simplest model in general agreement with observed phenomena is the Lambda-CDM model—that is, that clustering and merging allows galaxies to accumulate mass, determining both their shape and structure. Hydrodynamics simulation, which simulates both baryons and dark matter, is widely used to study galaxy formation and evolution.
Hubble's law, also known as the Hubble–Lemaître law, is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving away from Earth. The velocity of the galaxies has been determined by their redshift, a shift of the light they emit toward the red end of the visible spectrum.
In cosmology and physics, cold dark matter (CDM) is a hypothetical type of dark matter. According to the current standard model of cosmology, Lambda-CDM model, approximately 27% of the universe is dark matter and 68% is dark energy, with only a small fraction being the ordinary baryonic matter that composes stars, planets, and living organisms. Cold refers to the fact that the dark matter moves slowly compared to the speed of light, giving it a vanishing equation of state. Dark indicates that it interacts very weakly with ordinary matter and electromagnetic radiation. Proposed candidates for CDM include weakly interacting massive particles, primordial black holes, and axions.
The Lambda-CDM, Lambda cold dark matter or ΛCDM model is a mathematical model of the Big Bang theory with three major components:
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Amy J. Barger is an American astronomer and Henrietta Leavitt Professor of Astronomy at the University of Wisconsin–Madison. She is considered a pioneer in combining data from multiple telescopes to monitor multiple wavelengths and in discovering distant galaxies and supermassive black holes, which are outside of the visible spectrum. Barger is an active member of the International Astronomical Union.
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The Local Void is a vast, empty region of space, lying adjacent to the Local Group. Discovered by Brent Tully and Rick Fisher in 1987, the Local Void is now known to be composed of three separate sectors, separated by bridges of "wispy filaments". The precise extent of the void is unknown, but it is at least 45 Mpc across, and possibly 150 to 300 Mpc. The Local Void appears to have significantly fewer galaxies than expected from standard cosmology.
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Misty C. Bentz is an American astrophysicist and Professor of Physics and Astronomy at Georgia State University. She is best known for her work on supermassive black hole mass measurements and black hole scaling relationships.
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