All Of Galaxy Formation Theory Is Wrong, Says Scientist

All Of Galaxy Formation Theory Is Wrong, Says Scientist

A legitimate headline - with the caveats of this being an arXiv-only article not submitted to any journal.

You might remember Mike Disney's last arXiv-only article in which he claimed that there were a huge number of optically faint or dark galaxies that had escaped detection in previous searches. That idea was more or less already vindicated by the discovery of huge numbers of extended, faint galaxies in clusters, though the other idea that they were missed in hydrogen surveys due to misidentifications looks to be very wrong.

Mike's latest offering turns that idea bizarrely on its head, assuming now (God knows why) that the very faint galaxies don't actually exist at all. In that case there are a number of strange "scaling relations" that the standard model of galaxy formation (hierarchical merging of smaller galaxies to build up larger ones) just can't explain. Some of these arguments might be interesting - e.g. all galaxies appear to have similar average brightnesses, gas density, and overall mass density (including dark matter). There's no obvious reason why that should be in a merging scenario, but if galaxies all formed by monolithic collapse in the uniformish-density early Universe it would make more sense.

Except that this completely ignores the newly-discovered ultra-faint galaxies, which certainly have much lower brightness densities and many probably have very different dark matter contents compared to normal galaxies of similar size and brightness. And that's one hell of a detail to overlook.

Personally I'm still rather skeptical of hierarchical merging - there are some things we know it can't explain, and monolithic collapse is a much simpler idea. If there was ever a case where I'd bet it'll turn out to be something in the middle, it'd be this.

There are two things I like about this article : 1) Mike throws caution utterly to the wind and considers an entirely different model of galaxy formation, which I think is an interesting speculative exercise to be encouraged more often provided it isn't taken to seriously; 2) The narrative writing style is easily ten times better than most papers. Instead of skimming the abstract and conclusions and figures and all that nonsense you can just start reading from beginning to end. Each section builds part of the narrative and the language is not the sadistically formal normally expected in refereed papers. And there's some very interesting stuff on using Bayesian statistics to assess evidence at the end, but that's a topic in itself (Mike's written but not published a book on that, which I've read - it's excellent).

The conclusions ? Sod 'em, it's a good read and I like the approach.
https://arxiv.org/abs/1703.00363