Boötes Void: structure and cosmology of voids

Boötes Void: The Largest Cosmic Void and Its Role in Cosmology

Cosmic voids are vast regions of the universe with extremely low galaxy densities, stretching across hundreds of millions of light-years. They were discovered in 1978 independently by Stephen Gregory and Laird Thompson in the US, and by Jaan Einasto and his team in the USSR. Voids form the cosmic web—a network of galaxy filaments and walls separated by these empty spaces. Voids expand faster than the rest of the universe, pushing matter toward their edges and shaping large-scale structures.

Galaxy density in voids is orders of magnitude lower than in superclusters like Laniakea (home to over 100,000 galaxies). Void dynamics tie into the cosmic microwave background (CMB): cold spots on its map correspond to voids, where early density fluctuations drove matter evolution.

Boötes Void: Parameters and Characteristics

The Boötes Void (also known as the Great Nothing) was discovered in 1981 by Robert Kirshner from Harvard University. It's located about 700 million light-years from Earth, with a diameter of 250 million light-years (0.27% of the observable universe). Initially, just 7 galaxies were identified; by 1995, that number rose to 27, and now it's up to 60.

The sparseness is so extreme that if the Milky Way sat at its center, our nearest neighbors wouldn't have been spotted until the 1960s. The void consists of dim, ordinary matter rather than dark matter, making it perfect for studying behavior under weak gravity.

Key features:

• Diameter: ~250 Mpc (megaparsecs).
• Distance: ~700 Mpc.
• Galaxies: 60+.
• Density: <1% of the universe's average.

Scientific Importance of Voids

Voids provide a pristine lab for probing dark energy, dark matter, and cosmic inhomogeneities. Key research areas include:

• Galaxy dynamics: Modeling galaxy and cluster motions in voids, and how they form filaments and walls.
• Expansion: Voids grow faster than average, testing inhomogeneous cosmology models as alternatives to dark energy.
• Quantum effects: Weak gravity is ideal for hunting Casimir effects and false vacuum signatures.
• Missing matter: Searching for dark and exotic matter in low-density environments.
• Galaxy evolution: Void galaxies are smaller, gas-rich, and show blue-shifted spectra.
• Cosmic web: Analyzing filament connectivity and potential structure breakdown under expansion.

These topics tie into background cosmology and the CMB.

Galaxies in the Boötes Void

Despite the emptiness, the void hosts notable galaxies. Markarian 845 is the brightest (magnitude 14.8), a spiral galaxy edge-on with a brilliant core, spanning about 1 arcminute.

Other examples:

• CG 692: Magnitude 15.2, distorted spiral arm, bright bulge, 0.7 arcminutes long.
• CG 538: Compact, magnitude 15.3, elliptical disk, 0.5 arcminutes across—looks star-like.
• I Zwicky 81: Disk galaxy with a bright central region.
• MCG+01-02-015: Barred spiral, the closest at 100 Mpc.

These galaxies show unusual evolution due to their isolation.

Voids in the Multiverse Context

The Eridanus Supervoid (6–10 billion light-years across) appears as a cold anomaly in the CMB. Leading hypotheses:

• Voids speed up expansion due to dominant dark energy.
• Collisions with multiverse bubbles (Markus Chown, 2007): Energy leaks carve out voids.
• Sponge-like universe (James Trefil): Voids stabilize matter distribution.

Speculation about artificial origins (Type III civilizations) is dismissed—voids are natural features.

Key Takeaways

• Boötes Void is the largest known, unlocking secrets of dark energy and matter.
• Void galaxies evolve differently: smaller, gas-rich, with blue spectra.
• CMB links confirm voids' role in the early universe.
• Multiverse theories cite voids as collision evidence.
• Void expansion tests the uniformity of cosmological laws.

— Editorial Team