THE DARK SIDE OF ASTRONOMY

By: Umaama Hussain

Dark matter is a form of matter that is hypothesized to account for 85% of matter in the universe whose presence is required to explain many astrophysical observations. Dark matter is called dark because it does not seem to interact with the electromagnetic field and is thus, difficult to detect.

Gravity stands to be the best and also the least understood phenomenon that nature can provide. Isaac Newton, the first to realize that gravity is a result of the attractive force between matter, described this force with a simple algebraic equation. Then, Albert Einstein, the first to successfully expound on Newton’s realization, described gravity as a force that warps the fabric of space-time due to matter and energy, with a not-so-simple algebraic equation.

These two beloved equations of gravity had yet to fail us. That is, until the year 1937 when astrophysicist Fritz Zwicky discovered that the universe was ‘missing’ 85% of its mass.

Zwicky, who was studying the movements of galaxies in the Coma cluster, found the average velocities of these galaxies to be absurdly high. Now, we know that larger gravitational forces induce higher velocities in the objects they attract, thus, the cluster must have an enormous mass. Yet, when the mass of each member galaxy was summed up, the Coma cluster did not contain nearly enough visible galaxies, and thus, mass and gravity, to account for the enormous speeds observed by Zwicky.

Additionally, these speeds exceeded the calculated escape velocity for its cluster – which then, should mean the cluster should have rapidly flown apart only a couple hundred millennia after it was formed. However, the Coma cluster is more than ten billion years old (nearly the age of the universe) and still perfectly, and puzzlingly, intact. This issue is prevalent in other clusters that were studied as well. Some form of matter must exist that holds these clusters together.

In 1967, astrophysicist Vera Rubin found a similar mass anomaly in spiral galaxies themselves. She discovered that isolated gas clouds and bright stars far out in the rural regions of galaxies retained high orbital speeds, and, in fact, increased with distance; they should have been falling due to the lack of visible matter adding to the gravity field in the exterior regions of the galaxy. Haloes of matter, that we cannot detect, must somehow exist on the edges of spiral galaxies, providing the increased velocities to these isolated objects.

Additionally, after the big-bang, gravity wished to concentrate matter, and expansion wished to dilute it. Gravity won this battle, however, resulting in the structure of the universe that we have today. However, gravity from ordinary matter could not have done this alone. Six times as much as ordinary matter is needed to provide this gravity – exactly the amount of matter that was measured to be ‘missing’.

Hence, the fact that there is a discrepancy between the amount of mass measured in the visible universe, and the amount of mass estimated from total gravity cannot be ignored. This bulk of gravitational force must arise from a substance that we cannot measure. Or maybe this excess gravity does not come from matter or energy at all but from some other conceptual subject that we do not yet understand. Or maybe it is not the matter that is the problem, but the gravity itself...

The questions keep piling up, but they are yet to be answered. Newton and Einstein have done their part and now, the scientific community is waiting on the next genius in line to come solve this great gravitational mystery of dark matter.

CITATIONS

1. “Dark Matter.” Wikipedia, Wikimedia Foun

2. dation, 19 Nov. 2021, https://en.wikipedia.org/wiki/Dark_matter.

3. Grasse, Tyson Neil De. Astrophysics for People in a Hurry. W. W. Norton & Company, 2017.