The Cluster-Merger Shock in 1E 0657-56

Understand

The merging galaxy cluster 1E 0657-56, known as the "bullet cluster," is one of the hottest clusters known.

• The X-ray emitting plasma exhibits bow-shock-like temperature and density jumps.
• The segregation of this plasma from the peaks of the mass distribution determined by gravitational lensing has been interpreted as a direct proof of collisionless dark matter.
• If the high shock speed inferred from the shock jump conditions equals the relative speed of the merging CDM halos, however, this merger is predicted to be such a rare event in a LCDM universe that observing it presents a possible conflict with the LCDM model.