[aerohead]

Sensors appears to be the challenge.
Astronomer Fritz Zwicky 'discovered' dark matter in 1937 by default, while attempting to reconcile discrepancies between fugacity and VIRIAL Theorem, kinetic energy, versus known mass in the galaxy. The mathematics pointed directly at 'hidden' mass ( dark matter ).
In 1970, astronomer Vera Rubin couldn't reconcile galactic rotation, orbital velocities, doppler effect, steller velocity vs mass orbiting far from the galactic center.
For the math to work, orbits must be enclosing more mass to explain orbital velocity.
The 'visible' galaxy could only be a small fraction of total mass.
They've ruled out:
* stars
* dust
* cool gas
* neutrons
* protons
* infrared signals
* radio signals
* absorbancy of light
* participation in nuclear reactions
So far, all they can do is observe how light is bent by the gravity of the dark matter.