Object type Void Declination +18.0° | Right ascension 18 38 Size 60 Mpc (200 Mly) | |
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 (150 million light-years) across and may have a long dimension of up to 70 Mpc (230 million light-years). The Local Void also appears to have significantly fewer galaxies than expected from standard cosmology.
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Location and dimensions
Voids are the result of the way gravity causes matter in the universe to "clump together", herding galaxies into clusters and chains, which are separated by regions mostly devoid of galaxies.
Astronomers have previously noticed that the Milky Way sits in a large, flat array of galaxies called the Local Sheet, which bounds the Local Void. The Local Void extends approximately 60 megaparsecs (200 Mly), beginning at the edge of the Local Group. It is believed that the distance from Earth to the centre of the Local Void must be at least 23 megaparsecs (75 Mly).
The size of the Local Void was calculated due to an isolated dwarf galaxy located inside it. The bigger and emptier the void, the weaker its gravity, and the faster the dwarf should be fleeing the void towards concentrations of matter. Dark energy has been suggested as an alternative explanation for the speedy expulsion of the dwarf galaxy.
An earlier "Hubble Bubble" model, based on measured velocities of Type 1a supernovae, proposed a relative void centred on the Milky Way. Recent analysis of that data, however, suggested that interstellar dust had resulted in misleading measurements.
Effect on surrounds
Scientists believe that the Local Void is growing and the Local Sheet, which makes up one wall of the void, is rushing away from the void's centre at 260 kilometres per second. Concentrations of matter normally pull together, creating a larger void where matter is rushing away. The Local Void is surrounded uniformly by matter in all directions, except for one sector in which there is nothing, which has the effect of taking more matter away from that sector. The effect on the nearby galaxy is astonishingly large. The Milky Way's velocity away from the Local Void is 270 kilometres per second (600,000 mph).
List of void galaxies
Several void galaxies have been found within the Local Void, these include: