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Galaxies & Cosmic Structures

Cosmic Voids

Cosmic voids are enormous regions of space that contain far fewer galaxies than average.

They make up most of the volume of the universe and are not entirely empty.

  1. Observe

    Large patches in galaxy surveys with few galaxies.

  2. Measure

    3D galaxy maps and their densities.

  3. Model

    Simulations show voids growing as matter drains toward filaments.

  4. Explain

    The web has holes, and they are as informative as the walls.

What is it?

A cosmic void is a region tens to hundreds of millions of light-years across in which galaxies are sparse. Voids are the empty spaces between the filaments of the cosmic web and occupy most of the universe's volume.

They are not completely empty. They contain some dwarf galaxies, gas and dark matter at low density. The Boötes Void is often quoted at roughly 300 million light-years across, though void boundaries depend on how they are defined.

How does it happen?

  1. Stage 1
    Slightly underdense region in the early universe
  2. Stage 2
    Gravity pulls matter to surrounding regions
  3. Stage 3
    Void grows and empties
  4. Stage 4
    Galaxy maps show a low-density region

What do we actually observe?

Low galaxy counts
Surveys see gaps in the galaxy distribution.
Shape
Voids tend to be roughly spherical as they expand.

How do scientists detect it?

  • Redshift surveys. DESI and SDSS map galaxy positions in three dimensions.

Why does it matter?

  • Because voids are dominated by dark energy's influence rather than gravitational clumping, they are a sensitive test of cosmological models.
  • They show how galaxy properties depend on environment.

The SpaceWeatherTracker connection

Voids are a reminder that the universe on large scales is structured, a very different regime from the solar system, where SpaceWeatherTracker measures conditions in real time.

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

Cosmic Voids: common questions

Are cosmic voids empty?

No. They contain very few galaxies, but still have some gas, dwarf galaxies and dark matter.

How big is the biggest void?

Sizes depend on definition, but large voids span hundreds of millions of light-years.

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