A massive blow for ACDM - the high redshift, mass, and collision velocity of the interacting galaxy cluster El Gordo contradicts concordance cosmology

El Gordo (ACT-CL J0102-4915) is an extremely massive galaxy cluster (M-200 approximate to 3 x 10(15) M-circle dot) at redshift z = 0.87 composed of two subclusters with a mass ratio of 3.6 merging at speed V-infall approximate to 2500 km s(-1). Such a fast collision between individually rare massive clusters is unexpected in Lambda cold dark matter (ACDM) cosmology at such high Z. However, this is required for non-cosmological hydrodynamical simulations of the merger to match its observed properties. Here, we determine the probability of finding a similar object in a ACDM context using the Jubilee simulation box with a side length of 6h(-1) Gpc. We search for galaxy cluster pairs that have turned around from the cosmic expansion with properties similar to El Gordo in terms of total mass, mass ratio, redshift, and collision velocity relative to virial velocity. We fit the distribution of pair total mass quite accurately, with the fits used in two methods to infer the probability of observing El Gordo in the surveyed region. The more conservative (and detailed) method involves considering the expected distribution of pairwise mass and redshift for analogue pairs with similar dimensionless parameters to El Gordo in the past light-cone of a z = 0 observer. Detecting one pair with its mass and redshift rules out ACDM cosmology at 6.16 sigma. We also use the results of Kraljic and Sarkar to show that the Bullet Cluster is in 2.78 sigma tension once the sky coverage of its discovery survey is accounted for. Using a chi(2) approach, the combined tension can be estimated as 6.43 sigma. Both collisions arise naturally in a Milgromian dynamics (MOND) cosmology with light sterile neutrinos.

Automated summary

The research analyzed the formation and properties of the galaxy cluster El Gordo, and determined the probability of finding a similar cluster in a ΛCDM cosmology through simulations of turnaround pairs. The study results indicate that the properties of El Gordo and the fast collision between two individually rare massive clusters are unexpected, potentially revealing new cosmological theories.