‘Dark matter’ is an essential ingredient to form stars naturally given only standard known physics. ‘Dark matter’ is a hypothetical exotic form of matter, unknown to laboratory physics, which does not interact with or emit light in any way, hence it is invisible to all forms of detection within the electromagnetic spectrum, from radio-waves to gamma radiation. ‘Dark matter’ itself, therefore, is outside of standard known physics. It is made-up stuff that has been given one special property, which is that it gravitates, that is, unlike normal matter, it is a source of gravity only.
Detection of ‘dark matter’
But has dark matter been discovered by any direct measurement? That is apart from inferring its existence due to anomalies like galaxy rotation curves where the motions of stars and gases in the arms of spiral galaxies do not follow the expected Keplarian law in line with standard Newtonian physics? No, it has not and that is after 40 years of searching in laboratory experiments. Yet it is believed to exist—a ‘god of the gaps’—and is essential, otherwise many astrophysical observations just do not agree with those expected by application of standard laws of physics. See Fig. 1 for image of dark matter.
Theoretical physicist Mordehai Milgrom has proposed an alternative to dark matter, called Modified Newtonian Dynamics (or MOND) wherein he slightly changes the law of gravitation on the very large-scale of galaxies to solve the problem of galaxy rotation curves and dynamics of galaxies on larger scales.