Keith Dixon-Roche (one of CalQlata's Contributors) asked himself the question; "does dark matter really exist?", given that a celestial atmosphere would have caused all celestial orbits to stop long ago.
'Dark Matter' was originally proposed by a couple of physicists (Fritz Zwicky & Jacobus Kapteyn) early in the 20th century simply because they ...
a) ... couldn't see anything at the centre of our galaxy so they assumed it was empty, and;
b) ... that the Milky Way’s stars should be thrown into outer space due to centrifugal force if they have no force-centre.
They knew a galactic force-centre was necessary to hold its satellites in orbit, but if there was nothing there, only 'dark matter' could be responsible.
They were of course correct, in that every orbital system must have a force-centre - Isaac Newton told us this 300 years ago - but because they had no idea where planetary and stellar heat came from, they simply assumed that a galactic force centre must be brighter than a star simply because it is bigger, and if it isn't there (they could not see it) it must be non-existent. They came up with the idea that all galactic space was full of 'dark matter', and that this acted as a force-centre.
The problem with their solution, however, is that a gas, i.e. 'dark matter', cannot act as a force-centre because it has no centre of mass. Nothing is gravitationally attracted to a gas.
Understanding Newton's laws of orbital motion, all galaxies must have a force-centre ('m₁'), because that is how orbits work. There is no work-around.
So, why can’t we see it?
For reasons of brevity, I shall refer to 'the Milky Way's galactic force-centre' as "Hades".
The reason we cannot see Hades is because it is cold; less than 10K, so it's dark. It radiates EME at wavelengths greater than 0.0087m (ƒ < 3.44E+10Hz), so it would have appeared invisible through a telescope.
Elliptical orbits are responsible for generating planetary (and stellar) heat, which means that if Hades were to generate heat, it would have to be in an elliptical orbit, but it isn't, it is in a linear orbit. Like all galaxies, Hades is travelling away from the great attractor in a straight-line, so it generates no internal heat. This is why it is cold, and therefore dark.
But we can use Newton's laws of orbital motion to find out quite a lot about Hades; for example its mass and spin-rate:
NASA tells us that its;
orbital perigee; Rᴾ = 2.4653729E+20m
orbital apogee; Rᴬ = 2.545251E+20m
orbital period; t = 7.258248E+15 seconds
which gives a major axis half-length; a = (Rᴾ+Rᴬ)/2 = 2.505312E+20 m
This means that the Milky Way's constant of proportionality is; K = a²/t³ = 3.35025745E-30 m²/s³
and
Hades' mass may be found from; m₁ = (2π)² / G.K = 1.76572019E+41 kg
and
Hades' spin rate may be found from; E₂ = E₁ - E₀ -E₃
where each of the rotational energy components may be found using spin theory, giving us;
E₁ & E₀ are zero and E₃ = -4.37816E+51 J
Therefore; E₂ = -4.37816E+51 J
Because it is cold, its density should be slightly higher than that of iron;
ρ ≈ 9000 kg/m³ and its radius; r = 1.67313E+12m
and because there is little or no mobility in Hades' matter, giving a radial modifier of 1, we may calculate Hades polar moment of inertia thus:
J = ⅖.m.r² = 1.977163E+65 J
and from; E = ½.J.ω.|ω|
ω = √[2.E/J] = 2.104455E-07 ᶜ/s
Because; a = 2.505312E+20 m and r = 1.67313E+12 m
and the radius of an iron atom is; Rᵢ = 7.6113534E-08 m,
R = a.Rᵢ/r = 11.39709109 m
In other words, looking for Hades through a telescope would be like looking for a black iron atom in the middle of an 11.4-metre diameter black disk.
That's why Fritz Zwicky & Jacobus Kapteyn couldn't see it. But it was (and still is) there!
To conclude; there was never any need for 'dark matter'; so why invent it?
Moreover, the world's physicists subsequently invented another fantasy that obviated the need for it; 'black holes', so why do so many physicists still believe in dark matter?
You will find further reading on this subject in reference publications(55, 60, 61, 62, 63 & 64)