Galaxies · Space Codex
The cosmic web
On the largest scales galaxies trace a web of filaments around vast empty voids.
Filaments, voids and Laniakea
At a glance
Key points
Our galaxy belongs to Laniakea, a supercluster about 520 million light-years across.
- Galaxies line filaments around voids
- We live in Laniakea
- A cosmic filament was imaged directly in 2025
Mapped by motion
Laniakea, Hawaiian for 'immeasurable heaven', was defined in 2014 by tracking how about 8,000 galaxies flow. The Local Group sits on its outskirts.
How the web formed
Tiny density ripples, visible today in the cosmic microwave background, grew under gravity. Dark matter, about 85% of all matter, collapsed first into sheets and filaments, and gas flowed along them into the knots where galaxies and clusters formed. Voids emptied as matter drained towards their edges. Computer simulations such as the Millennium Simulation of 2005, which followed about 10 billion particles, reproduce this sponge-like pattern closely.
Walls and voids
Redshift surveys of the 1980s revealed the pattern. In 1981 Robert Kirshner and colleagues reported a vast, nearly empty region in Boötes, and in 1989 Margaret Geller and John Huchra found a 'Great Wall' of galaxies stretching hundreds of millions of light-years. Today DESI has charted more than 47 million galaxies and quasars in three dimensions, tracing the web across much of cosmic history.
Seeing the strands
The gas in filaments is thin and faint. In 2025 a team led by Davide Tornotti used the MUSE instrument on ESO's Very Large Telescope for hundreds of hours to image the hydrogen glow of a filament about 3 million light-years long, whose light set out when the universe was about 2 billion years old.
What we still don't know
How much of the universe's ordinary matter hides in hot, diffuse gas along the filaments, and whether the very largest structures claimed in surveys fit the standard cosmological model.
Related entries
- The Milky WayOur barred spiral home galaxy
- Dark matter and dark energyThe 95% we cannot see
Sources
- Tully et al. 2014, Nature (arXiv) (opens in a new tab)
- Max Planck Society: direct image of the cosmic web (opens in a new tab)
- Britannica: observable universe (opens in a new tab)
- Kirshner et al. 1981, ApJ 248:L57 (opens in a new tab)
- Geller & Huchra 1989, Science 246:897 (opens in a new tab)
- MPA: the Millennium Simulation Project (opens in a new tab)
- IFAE: DESI completes planned 3D map of the universe (Apr 2026) (opens in a new tab)
Last reviewed against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.