You can’t see it. You can’t hear it. It does not emit any type of electromagnetic radiation that can be recorded, nor does it affect or be affected by light, but it is out there and according to cosmologists, it accounts for the majority of matter in the universe.
Something must account for the additional gravitational properties that are affecting objects in space, after taking into account the ‘normal’ gravitational affects occurring from the objects themselves (e.g. a star, planet, galaxy, etc.), hence, astrophysicists have hypothesized that it is dark matter that is causing this additional gravitational drag.
More specifically, it is calculated by the discrepancies between the gravitational pull between objects in the universe, called “luminous matter” and their gravitational effects and other entities, which in this case is perceived to be dark matter. It is estimated that dark matter consists of 84.5% of the total matter in the space.
Vera Rubin, an astronomer at the Department of Terrestrial Magnetism at the Carnegie Institution of Washington who was studying galaxy rotation rates was the first to observe this gravitational discrepancy in the 1960s.
Galaxy rotation rates, also called curves and velocity curves are acquired through the measurement of the disc galaxies as the stars and gas accelerate from galaxy’s center and are recorded (plotted) against the body’s distance from the galaxy’s center.
Rubin was using a sensitive spectrograph that could measure the velocity curve of spiral galaxies to a much greater degree of accuracy than had ever been accomplished before. She presented her findings at a meeting of the American Astronomical Society in 1975. Rubin’s calculations proved that most galaxies has to contain about six times as much dark mass from what can be accounted for by visible matter. Shortly after that, other cosmologists observed and agreed with Rubin and the term Dark Matter was given to this phenomena.
Scientists are still studying dark matter, along with all the other phenomena that brings more questions than answers in the known universe. Hopefully, scientists will be able to unravel these haunting questions within this 21st century, and in so doing, may bring us closer to understanding ourselves.