Abstract
Abstract
The colliding galaxy clusters system 1E 0657-56, the “Bullet Cluster,” is often presented as a serious objection to modified gravity theories dispensing with dark matter in general, and in particular, to the MOND formalism. The argument centers on the fact that the baryonic matter distribution of this system is dominated by the X-ray emitting gas, while the projected surface density required under General Relativity (GR) to explain the observed lensing signal, centers on the observed galaxies. This spatial offset is interpreted as being in conflict with MOND, naively assuming that dark matter being absent, the gravitational potential should center upon the largest mass distribution, the X-ray gas. However, as under GR, under MOND, the gravitational potential of a system depends upon the volume density and not just the total mass. Here, I show that the surface density that QUMOND predicts will be inferred under GR from the gravitational potential of the “Bullet Cluster,” qualitatively matches the spatial distribution of what GR inferences of lensing observations return. The close-to-pointlike galaxies imply under QUMOND a relatively larger surface density signal than what is expected from the diffuse gas. As is common under MOND modeling of galaxy clusters, a mass deficit on the baryon content is obtained, in this case by a factor of 1.6. Beyond this, only small offsets on the details with respect to GR interpretations of lensing observations remain; MOND is, hence, shown to be no more discrepant with the “Bullet Cluster” than with any other galaxy cluster.