The basic claim is that instead of being essentially stable systems, galaxies are in a continual state of disintegration. Hence there's no need for dark matter or modifying gravity to hold galaxies together, because they're simply exploding.
Anyone who has played with firework spinners as a child (or an adult) must have noticed their resemblance to spiral galaxies. Anyone who has not can always search “firework spinner” on YouTube to see it. The trajectories of the glowing embers in a spinner look like the stars of the spiral arms.
But wait, it gets better.
Quite obviously, the actual motion of the stars cannot be observed directly.
I think you'll find that it can. And indeed already has been for very large numbers in the Milky Way. Of course, the leading project is the Gaia spacecraft, which has had plenty of press coverage. True, it's very difficult to do this for other galaxies, but it is possible. And it's not even remotely sensible to assume our Milky Way is stable while all other galaxies are not.
But the still picture that we see suggests non-circular trajectories (like the firework spinner) rather than the circular trajectories as assumed by most analyses.
No, it does not. Literally nothing about them suggests that.
In the first model, a spiral galaxy is considered to start as a compact spherical core surrounded by a functionally rigid spinning disk held together by gravity as well as electromagnetic scattering forces (see section IV).
Mercifully, EM forces are only mentioned as a hand-waving, "and there might be EM forces as well" token comment rather than in any detail.
Here, in the simplest version of this model, we will assume that the stars separate from the disk edge with initial velocities equal to that of the edge.
Well, then, disintegration would be extremely rapid. Look, here's a simulation I made earlier !
The explosion of the outer parts of a typical spiral galaxy would be extremely rapid indeed : < 100 Myr. Given that we see large numbers of spiral galaxies over most of the Universes ~13 Gyr history, and none at all looking like their exploded remnants, this idea is immediately falsified. But let's press on regardless.
As an individual star moves away from the core, its outward radial speed increases and could eventually become measurable. However, several mitigating factors are expected to make such measurement difficult. First, the density of stars decreases with increasing radial distance.
Well that bit's actually true. But it isn't going to make the measurements difficult if you can measure the velocities of individual stars - which is what you have to do to get 3D motions. So far as I know there's no way to measure bulk proper motions, unlike radial measurements where you can get the average velocity field. I suppose you could do it statistically to reduce the errors by measuring lots of stars in the same region, but you'll still be measuring the velocities of individual stars.
Second, the stars at greater radial distances are expected to be colder and dimmer.
A heck of an assumption given the complexities of star formation, and essentially wrong for individual stars. In the 100 Myr of the galaxy's disintegration, the very brightest stars will die off, but most will be unaffected.
For the second model, one may consider the early stage of a spiral galaxy to be a compact ball of matter with significant angular momentum. This compact object could explode due to maybe a thermonuclear event.
Eh what ? No, seriously, what ?
The explosion fragments are expected to be of a wide range of sizes. Granular particles or even particles of atomic size would be the primary fragments. Let us call this collection of small fragments the dust plume.
NO ! Let's not do that, because plumes are linear features and you haven't described why it should be linear or which orientation the feature should have. Consequently the rest of the model is rendered unintelligible. So far as I can tell, the bulk of the mass is ejected at relativistic speeds, leaving the stars exposed and expanding much more slowly (~100 km/s). He calculates that the plume speed is (of course) so great that it disappears almost instantly compared with the motions of the stars. But then :
Hence, Doppler shift is the only means of measuring their speed.
Not in the Milky Way it isn't. And you could predict what the disintegrating galaxies would look like. Guess what ? They don't look like that.
I freely confess to a perverse approval of lunatic papers on arXiv. Sometimes debunking is good for the soul.
https://arxiv.org/abs/1801.09304
I thoroughly enjoy reading posts like this.
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