> dark matter doesn't explain the heat issue You're right. Collisional matter that dissipates radiatively completely explains the heat issue: many of the ind

> dark matter doesn't explain the heat issue You're right. Collisional matter that dissipates radiatively completely explains the heat issue: many of the individual components of the dust and gas in the galaxy clusters came close enough to each other to interact electromagnetically, trading off their momentum-energy for momentum-energy in photons and other products of scatterings. Ordinary intergalactic gas and dust from the two clusters got squashed together and the squashing made it hot enough to glow. In the standard cosmology (\Lambda-CDM), CDM is cold dark matter that is collisionless, does not dissipate radiatively and does not feel electromagnetism even in very close quarters. So it does not heat up, and its momentum is only influenced the gravitation sourced by the components of the colliding galaxy clusters (which includes the dark matter itself), with the result that the "clouds" of dark matter in each cluster sail right through one another and past all the ordinary matter, with effectively no deflections of their trajectories. The result is that gravity (measured by lensing of background objects) points to a hot cloud of dust left in the middle of the collision, the stars and other denser visible ahead of that debris, and two mostly-transparent regions leading the way ahead of the visible matter. > the bullet is anomalous in multiple ways It's a bit more accurate to say that there are questions still unanswerable by observation of the bullet cluster alone, and that searches for other cluster collisions are likely to provide further partial answers. In particular, further observations will favour or disfavour different numerical simulations of large scale structure formation under the standard cosmology. However the variables most directly tested align roughly with whether cold dark matter is almost wholly particles similar to heavy sterile neutrinos or almost wholly particles like axions, rather than whether particle cold dark matter is there at all. Even TeVeS proponents aren't especially optimistic on that latter point (e.g. Angus and Diaferio, two prolific TeVeS-as-relativistic-MOND researchers, in their 2012 paper https://arxiv.org/pdf/1206.6231.pdf https://arxiv.org/pdf/1206.6231.pdf starting at the bottom of page 23).