The Boötes Void & Cosmic Supervoids
The Boötes Void (discovered by Kirshner et al. 1981) is an approximately spherical cosmic supervoid roughly 100 megaparsecs (330 million light-years) in diameter centered at redshift z ≈ 0.052 (~700 million light-years away). It is not a total vacuum: deep redshift surveys have identified ~60 star-forming galaxies within its volume—roughly 10–15% of the cosmic mean galaxy density—arranged along tenuous internal sub-filaments evacuated by divergent peculiar velocity flows.
Physical Mechanism & Dynamics
Supervoids evolve from primordial troughs in the Gaussian density field (δ_i < 0). Because a region with lower-than-average matter density experiences weaker self-gravity than the surrounding background universe, its effective local Hubble expansion rate H_void exceeds the global rate H(t). Matter flows outward from the void center toward the bounding filamentary walls, deepening the interior underdensity toward δ_m ≈ -0.8 to -0.9.
As smaller adjacent sub-voids expand and collide, the tenuous sheets separating them are stretched and drained—a process called the 'void-in-void' hierarchy (Sheth & van de Weygaert 2004). In the Boötes Void, residual tubular sub-filaments survive inside the supervoid, hosting isolated, gas-rich, low-metallicity late-type galaxies that have escaped ram-pressure stripping and major mergers.
Quantitatively, this mechanism is governed by Nonlinear Spherical Void Expansion & Evacuation (1 + δ_v(t) ≈ (1 - δ_lin(t) / 3)^(-3), v_outflow(r) ≈ (1/3) H(z) Ω_m(z)^0.55 |δ_v| r). Describes how a linear underdensity δ_lin < 0 maps into a deep nonlinear void density contrast δ_v → -0.85 with linear radial outflow velocity toward the bounding shell.
Nonlinear Spherical Void Expansion & Evacuation
1 + δ_v(t) ≈ (1 - δ_lin(t) / 3)^(-3), v_outflow(r) ≈ (1/3) H(z) Ω_m(z)^0.55 |δ_v| rDescribes how a linear underdensity δ_lin < 0 maps into a deep nonlinear void density contrast δ_v → -0.85 with linear radial outflow velocity toward the bounding shell.
Quantitative Benchmarks & Parameters
| Parameter / Observable | Measured Value / Scale | Method & Context |
|---|---|---|
| Boötes Void diameter | ~100 Mpc (330 million ly) | Kirshner et al. (1981, 1987) redshift survey |
| Center redshift & distance | z ≈ 0.052 (~215 Mpc / 700 Mly) | Heliocentric recession velocity cz ≈ 15,500 km/s |
| Known interior galaxies | ~60 galaxies (vs ~2,000 at mean density) | Hα, H I 21-cm, and SDSS spectroscopic surveys |
| Interior matter density contrast | δ_m ≈ -0.75 to -0.85 | Void galaxy counts & weak lensing profiles |
Observational Evidence & How Scientists Know
VLA 21-cm neutral hydrogen (H I) mapping and optical spectroscopy of Boötes Void galaxies (Szomoru et al. 1996) demonstrate that void galaxies have normal H I gas masses and elevated specific star formation rates compared to cluster galaxies of identical stellar mass, confirming that cosmic environment governs late-stage galaxy quenching.
Across reference datasets (Planck 2018 Cosmological Parameters (PR3), SIMBAD Astronomical Database (CDS)), quantitative benchmarks for the boötes void & cosmic supervoids are anchored by: Boötes Void diameter (~100 Mpc (330 million ly), via Kirshner et al. (1981, 1987) redshift survey); Center redshift & distance (z ≈ 0.052 (~215 Mpc / 700 Mly), via Heliocentric recession velocity cz ≈ 15,500 km/s); Known interior galaxies (~60 galaxies (vs ~2,000 at mean density), via Hα, H I 21-cm, and SDSS spectroscopic surveys); Interior matter density contrast (δ_m ≈ -0.75 to -0.85, via Void galaxy counts & weak lensing profiles).
Uncertainties, Systematics & Open Questions
Measuring the exact dark-matter floor inside deep supervoids requires stacking weak-lensing tangential shear profiles across thousands of SDSS/DESI/Euclid voids to separate luminous galaxy bias from true total matter density.
Real Astronomical Benchmarks & Cross-Domain Links
Boötes Void
Archetypal ~100 Mpc supervoid at z ≈ 0.052 containing ~60 galaxies
Eridanus Supervoid & CMB Cold Spot
Low-redshift supervoid line-of-sight aligned with the Planck CMB Cold Spot
Local Void
Nearby underdensity bordering the Local Sheet and pushing the Milky Way at ~260 km/s
Guided Learning Path
Related Concepts, Methods & Explorers
Scientific Sources & Provenance
- Planck 2018 Cosmological Parameters (PR3) (PR3 (2020 A&A 641, A6)) — Planck Collaboration, Aghanim, N., et al. 2020, A&A, 641, A6. Archive / Reference ↗
- SIMBAD Astronomical Database (CDS) (2026-10 release) — Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database). Archive / Reference ↗
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