In physical cosmology, galaxy filaments (subtypes: supercluster complexes, galaxy walls, and galaxy sheets) are the largest known structures in the universe. They are massive, thread-like formations, with a typical length of 50 to 80 megaparsecs h−1 (or of the order of 200 to 500 million light-years) that form the boundaries between large voids in the universe. Filaments consist of gravitationally bound galaxies. Parts wherein many galaxies are very close to one another (in cosmic terms) are called superclusters.
Discovery of structures larger than superclusters began in the late-1980s. In 1987, astronomer R. Brent Tully of the University of Hawaii’s Institute of Astronomy identified what he called the Pisces–Cetus Supercluster Complex.
In 1989, the CfA2 Great Wall was discovered, followed by the Sloan Great Wall in 2003.
Filament subtype of filaments have roughly similar major and minor axes in cross-section, along the lengthwise axis. Here are some of the filaments:
- Coma Filament- The Coma Supercluster lies within the Coma Filament. It forms part of the CfA2 Great Wall.
- Perseus–Pegasus Filament- Connected to the Pisces–Cetus Supercluster, with the Perseus–Pisces Supercluster being a member of the filament.
The galaxy wall subtype of filaments have a significantly greater major axis than minor axis in cross-section, along the lengthwise axis. Here are some of the galaxy walls:
- CfA2 Great Wall – This was the first super-large large-scale structure or pseudo-structure in the universe to be discovered. The CfA Homunculus lies at the heart of the Great Wall, and the Coma Supercluster forms most of the homunculus structure. The Coma Cluster lies at the core.
- Sloan Great Wall (SDSS Great Wall)- This was the largest known galaxy filament to be discovered, until it was eclipsed by the Hercules–Corona Borealis Great Wall found ten years later.
Large quasar groups (LQGs) are some of the largest structures known. They are theorized to be protohyperclusters/proto-supercluster-complexes/galaxy filament precursors. Here are some of the LQGs:
- Clowes–Campusano LQG- It was the largest known structure in the universe from 1991 to 2011, until U1.11’s discovery. Main distance is z=1.28. Longest dimension is 630 Mpc
- Huge-LQG- It was the largest structure known in the universe, until the discovery of the Hercules–Corona Borealis Great Wall found one year later. Main distance is z=1.27. Characteristic size: 500 Mpc. Longest dimension: 1240 Mpc
Next subtype of cosmic filaments is Galaxy supercluster- A supercluster is a large group of smaller galaxy clusters or galaxy groups; it is among the largest known structures of the universe. Here is one of many and its specification:
- Pisces–Cetus Supercluster Complex- Contains Virgo Supercluster and Local Group. It is 1 billion ly wide and 150 million ly deep.