The Coma Cluster & CfA2 Great Wall
The Coma Cluster (Abell 1656), situated 99 megaparsecs (323 million light-years) away, is a dense, spherical Abell richness class 2 cluster containing over 1,000 bright early-type galaxies orbiting two central supergiant cD ellipticals (NGC 4874 and NGC 4889) inside a ~1.2 × 10¹⁵ M☉ dark matter halo. It forms the central gravitational node of the CfA2 Great Wall, a 250-Mpc cosmic sheet mapped in 1989.
Physical Mechanism & Dynamics
In 1933, Fritz Zwicky applied the virial theorem (2K + U = 0) to radial velocities of eight Coma Cluster galaxies and found a velocity dispersion near 1,000 km/s, requiring a dynamical mass-to-light ratio hundreds of times greater than stellar populations alone—the first quantitative discovery of dark matter (dunkle Materie). Modern spectroscopy of >1,000 Coma members refines σ_v = 1,008 km/s and yields a composite mass profile of ~85% dark matter, ~13% hot X-ray intracluster plasma (k_B T ≈ 8.2 keV), and ~2% stars.
On larger scales, Geller and Huchra (1989) discovered via the Second Center for Astrophysics (CfA2) Redshift Survey that the Coma Cluster and the Leo Cluster (Abell 1367) are connected by a vast, flattened pancake of galaxies—the CfA2 Great Wall—spanning ~750 million light-years in length and 250 million light-years in width, but only ~16 million light-years thick.
Quantitatively, this mechanism is governed by Cluster Virial Mass Estimator (M_vir = (3 π / (2 G)) σ_los^2 R_H ≈ 1.2 × 10¹⁵ M☉). Relates the line-of-sight velocity dispersion σ_los ≈ 1,008 km/s and harmonic mean projected radius R_H of Coma Cluster galaxies to total gravitating mass.
Cluster Virial Mass Estimator
M_vir = (3 π / (2 G)) σ_los^2 R_H ≈ 1.2 × 10¹⁵ M☉Relates the line-of-sight velocity dispersion σ_los ≈ 1,008 km/s and harmonic mean projected radius R_H of Coma Cluster galaxies to total gravitating mass.
Quantitative Benchmarks & Parameters
| Parameter / Observable | Measured Value / Scale | Method & Context |
|---|---|---|
| Coma Cluster distance (z = 0.0231) | 99 ± 3 Mpc (323 million ly) | Fundamental Plane, SBF & Type Ia supernovae |
| Cluster virial mass M_200 | (1.2 ± 0.2) × 10¹⁵ M☉ | Weak lensing, X-ray hydrostatic & galaxy kinematics |
| Intracluster gas temperature | k_B T ≈ 8.2 keV (9.5 × 10⁷ K) | XMM-Newton, Chandra & SRG/eROSITA X-ray spectra |
| CfA2 Great Wall dimensions | 250 × 90 × 5 Mpc | CfA2 & SDSS redshift space mapping |
Observational Evidence & How Scientists Know
Deep Subaru Hyper Suprime-Cam imaging and HST ACS surveys revealed over 800 ultra-diffuse galaxies (UDGs) such as Dragonfly 44 in Coma, while LOFAR and VLA radio observations map a giant radio halo and peripheral relic shocks driven by ongoing subgroup accretion (NGC 4839 group).
Across reference datasets (SIMBAD Astronomical Database (CDS), Revised New General Catalogue and Index Catalogue (RNGC/IC)), quantitative benchmarks for the coma cluster & cfa2 great wall are anchored by: Coma Cluster distance (z = 0.0231) (99 ± 3 Mpc (323 million ly), via Fundamental Plane, SBF & Type Ia supernovae); Cluster virial mass M_200 ((1.2 ± 0.2) × 10¹⁵ M☉, via Weak lensing, X-ray hydrostatic & galaxy kinematics); Intracluster gas temperature (k_B T ≈ 8.2 keV (9.5 × 10⁷ K), via XMM-Newton, Chandra & SRG/eROSITA X-ray spectra); CfA2 Great Wall dimensions (250 × 90 × 5 Mpc, via CfA2 & SDSS redshift space mapping).
Uncertainties, Systematics & Open Questions
Whether the NGC 4839 subgroup on the southwest edge of Coma is on its first infall or returning after an off-axis core passage is actively constrained by eROSITA X-ray sloshing fronts and radio relic polarization.
Real Astronomical Benchmarks & Cross-Domain Links
NGC 4889 & NGC 4874
Binary supergiant cD galaxies at the gravitational core of the Coma Cluster, with NGC 4889 hosting a ~2.1 × 10¹⁰ M☉ black hole
Dragonfly 44
Prototypical dark-matter-dominated ultra-diffuse galaxy discovered in the Coma Cluster
Sloan Great Wall
Even larger 420-Mpc cosmic filament discovered beyond the CfA2 Great Wall
Guided Learning Path
Related Concepts, Methods & Explorers
Scientific Sources & Provenance
- SIMBAD Astronomical Database (CDS) (2026-10 release) — Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database). Archive / Reference ↗
- Revised New General Catalogue and Index Catalogue (RNGC/IC) (2024/2026 edition) — Steinicke, W. 2010, Observing and Cataloguing Nebulae and Star Clusters (Cambridge Univ. Press); Verga, M. OpenNGC (CC-BY-SA 4.0 / data tables). Archive / Reference ↗
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