The arXiv brought an early Xmas gift in the form of a measurement of the velocity dispersion of Crater 2. Crater 2 is an extremely diffuse dwarf satellite of the Milky Way. Upon its discovery, I realized there was an opportunity to predict its velocity dispersion based on the reported photometry. The fact that it is very large (half light radius a bit over 1 kpc) and relatively far from the Milky Way (120 kpc) make it a unique and critical case. I will expand on that in another post, or you could read the paper. But for now:
The predicted velocity dispersion is σ = 2.1 +0.9/-0.6 km/s.
The measured velocity dispersion is σ = 2.7 ± 0.3 km/s
as reported by Caldwell et al.
Isn’t that how science is suppose to work? Make the prediction first? Not just scramble to explain it after the fact?