What is Dark Matter?
The search for Dark Matter has been going for 90 years, ever since the idea was brought up by Fritz Zwicky, but the final answer turns out to be astoundingly simple.
Zwicky observed the gravitational properties of distant galaxies and galaxy clusters, and found that they behaved as if they contained much more matter (ten times as much) than was apparent from the stars they contained.
He was unable to identify the source of this extra gravitational influence, but called it "Dark Matter", and left it to others to discover. All sorts of exotic suggestions have been put forward since Zwicky's day, such as "Axions", theoretical matter which exerted gravity but did not give off light, and so appeared Dark. None of these suggestions withstood proper examination.
Now a simple and obvious answer has become available. In Zwicky's day the nature of ordinary stars like those in our home galaxy was known, but the nature of very distant stars, those in faraway galaxies, was not.
In the Milky Way, our home galaxy, most of the stars are Fusion Stars. They are glowing spheres of hot gases, within which energy is produced by fusion of hydrogen into helium and heavier elements. This energy is radiated as light in all directions, from the surfaces of the hot spheres.
In contrast, most of the light we detect from very distant objects comes from Vortex Stars. These are not spheres, but rapidly-rotating linear objects, emitting light in tight beams along their axes of rotation.
Viewing of an AGN from different angles
Vortex Stars include black holes, neutron stars, quasars, and AGNs. AGNs are the Active Galactic Nuclei at the centres of galaxies, also called supermassive black holes.
The vital point about Vortex Stars is that they emit light in tight beams, and this light is only seen when near to their beam axes. Away from this beam, a vortex star appears dark.
If you consider the hemisphere within which a beam propagates, at the end of the beam will be a keyhole within which the beam is seen. Away from the keyhole, the beam will not be seen, it will appear dark.
Diagram of keyhole size in viewing AGNs.
The relative size of the keyhole will depend on how much a beam spreads. This can be estimated in the real universe from photos of how the beam from an AGN such as the M87 Galaxy is scattered when it encounters a gas cloud. It turns out that the keyhole makes up about 10% of the viewing hemisphere.
In other words, wherever you turn your telescope to view distant AGNs, only about 1 in 10 of them will have their axial beams close enough to your viewing direction for them to be seen. The other 90% will not be seen. They will still exert normal gravitational action, but will appear as "Dark Matter".
Where to find more details
UG105: Obvious: The Solution to the Dark Matter puzzle
UG102: Understanding Vortex Stars: White Dwarfs, Neutron Stars, Black Holes, and AGNs
Item: LT251119.
Perth, Western Australia.
Last update 2025 Nov 28.
