The KBC Void (or Local Hole) is an immense, comparatively empty region of space, named after astronomers Ryan Keenan,

Amy Barger Amy J. Barger (born January 18, 1971) 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 wa ...

, and

Lennox Cowie Lennox Lauchlan Cowie FRS (born 18 October 1950, Jedburgh, Scotland) is a British astronomer, and professor at the Institute for Astronomy, University of Hawaiʻi. Biography In 1970, Cowie graduated from the University of Edinburgh with a BSc w ...

, who studied it in 2013. The existence of a local underdensity has been the subject of many pieces of literature and research articles. The underdensity is proposed to be roughly spherical, approximately 2 billion

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s (600

megaparsecs The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

, Mpc) in diameter. As with other

voids Void may refer to: Science, engineering, and technology * Void (astronomy), the spaces between galaxy filaments that contain no galaxies * Void (composites), a pore that remains unoccupied in a composite material * Void, synonym for vacuum, ...

, it is not completely empty; it contains the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

, the

Local Group The Local Group is the galaxy group that includes the Milky Way, where Earth is located. It has a total diameter of roughly , and a total mass of the order of . It consists of two collections of galaxies in a " dumbbell" shape; the Milky Way ...

, and the larger part of the

Laniakea Supercluster The Laniakea Supercluster (; Hawaiian language, Hawaiian for "open skies" or "immense heaven") or the Local Supercluster (LSC or LS) is the galaxy supercluster that is home to the Milky Way and approximately 100,000 other nearby galaxies. It w ...

. The Milky Way is within a few hundred million light-years of the void's center. It is debated whether the existence of the KBC void is consistent with the

ΛCDM model The Lambda-CDM, Lambda cold dark matter, or ΛCDM model is a mathematical model of the Big Bang theory with three major components: # a cosmological constant, denoted by lambda (Λ), associated with dark energy; # the postulated cold dark mat ...

. While Haslbauer et al. say that voids as large as the KBC void are inconsistent with ΛCDM, Sahlén et al. argue that the existence of supervoids such as the KBC void is consistent with ΛCDM. Galaxies inside a void experience a gravitational pull from outside the void, which yields a larger local value for the

Hubble constant 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 a galaxy is from the Earth, the faste ...

, 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

supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...

e and

Cepheid variable A Cepheid variable () is a type of variable star that pulsates radially, varying in both diameter and temperature. It changes in brightness, with a well-defined stable period (typically 1–100 days) and amplitude. Cepheids are important cosmi ...

s (72–75 km/s/Mpc) and from the

cosmic microwave background The cosmic microwave background (CMB, CMBR), or relic radiation, is microwave radiation that fills all space in the observable universe. With a standard optical telescope, the background space between stars and galaxies is almost completely dar ...

and baryon acoustic oscillation data (67–68 km/s/Mpc). 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. 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 Modified Newtonian dynamics (MOND) is a theory that proposes a modification of Newton's laws to account for observed properties of galaxies. Modifying Newton's law of gravity results in modified gravity, while modifying Newton's second law resul ...

gravity rather than

general relativity General relativity, also known as the general theory of relativity, and as Einstein's theory of gravity, is the differential geometry, geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of grav ...

. 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.

See also

References

Further reading