Great Attractor

The Great Attractor is a concentration of mass in the nearby universe whose gravity contributes to the motion of galaxies, including the Milky Way, toward the Norma Cluster region.

Peculiar velocity: A celestial body's velocity relative to the smooth expansion of the universe. The Great Attractor is inferred from galaxies' peculiar velocities toward its region.
Dipole Repeller: A large underdense region whose gravitational effect contributes to the observed motion of the Local Group. It shows that galaxy flows reflect both mass concentrations and vast empty regions.
Hubble's law: The relation between a galaxy's distance and its recession speed caused by cosmic expansion. Separating expansion from local motion is necessary to identify gravitational infall.
CMB dipole: The directional temperature variation in the cosmic microwave background caused mainly by the observer's motion. Its measured direction and amplitude constrain the Local Group's motion through space.
Cosmic flow: The large-scale pattern of galaxy motions produced by cosmic expansion and gravitational attraction. The Great Attractor is one contributor to the nearby universe's broader flow pattern.
Galaxy redshift survey: A survey measuring galaxy positions and redshifts to map large-scale cosmic structure. Redshift surveys traced structures in the obscured region and refined the attractor's location.
Dark matter: Matter inferred from gravity that does not emit or absorb detectable light. Unseen matter contributes to the mass shaping galaxy motions in the attractor region.
Tully-Fisher relation: An empirical relation between a spiral galaxy's luminosity and its rotational speed. Distance estimates using this relation helped reveal coherent motions across nearby galaxies.
Norma Cluster: A rich galaxy cluster in the constellation Norma, located in the region associated with the Great Attractor. This cluster lies near the center of the mass concentration's inferred pull.
Shapley Supercluster: A massive concentration of galaxy clusters in the direction of the constellation Centaurus. Its gravity contributes to motions once attributed more exclusively to the Great Attractor.

Linked from 10 pages