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Galaxies & Cosmic Structures

The Cosmic Web

On the largest scales, matter in the universe forms a web of filaments, sheets and clusters surrounding vast empty voids.

This large-scale structure grew from tiny density differences in the early universe, shaped by gravity and dark matter.

  1. Observe

    Galaxies arranged in filaments, walls and clusters, with voids between.

  2. Measure

    Positions and redshifts of millions of galaxies.

  3. Model

    Simulations of gravity acting on dark matter and gas.

  4. Explain

    The universe's structure grew from small seeds over 13.8 billion years.

What is it?

Galaxies are not spread evenly. Maps of millions of galaxies show them arranged along filaments and sheets that meet at dense nodes where galaxy clusters sit, with large underdense voids between them. This pattern is called the cosmic web.

The leading explanation is that slight variations in density, visible in the cosmic microwave background about 380,000 years after the Big Bang, grew under gravity. Dark matter is thought to provide most of the scaffolding. Supercomputer simulations reproduce the web well.

How does it happen?

  1. Stage 1
    Tiny density variations in the early universe
  2. Stage 2
    Gravity pulls matter together
  3. Stage 3
    Filaments and clusters form
    Voids empty out
  4. Stage 4
    Galaxies form along the web

What do we actually observe?

Filaments
Strings of galaxies and gas stretching for tens of millions of light-years.
Clusters
Nodes where filaments meet, holding hundreds to thousands of galaxies.
Voids
Regions with far fewer galaxies.

How do scientists detect it?

  • Redshift surveys. SDSS and DESI measure three-dimensional galaxy positions.
  • Weak lensing surveys. Trace the total mass, including dark matter.
  • Quasar absorption spectra. Reveal gas in filaments.

Why does it matter?

  • Its structure tests models of dark matter and dark energy.
  • It shapes where and how galaxies form.

The SpaceWeatherTracker connection

It puts the Sun's environment in perspective: the heliosphere sits inside the Milky Way, which sits inside a local part of the web.

This is an explainer. SpaceWeatherTracker does not show live data for this phenomenon; see the “Space Phenomena Now” section on the hub for what is currently monitored.

Related phenomena

Primary family: Galaxies & Cosmic Structures

The Cosmic Web: common questions

What is the cosmic web?

The large-scale network of filaments, sheets and clusters of galaxies and dark matter that surrounds giant voids.

How do we know it exists?

Galaxy surveys map it directly, and simulations that follow gravity and dark matter reproduce it.

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