Across the universe, dark matter has six times the total gravity of all visible matter. But what is dark matter? Why are scientists not able to detect it? Is it the same as aether? Let’s deal with these questions in this article.
Fritz Zicky is a known astrophysicist who detected an unusual presence in the Coma cluster. The average velocity of galaxies in this cluster exceeds their escape velocity and they all should have been scattered by now. However, this is not the scenario.
Coma cluster isn’t the only cluster. Across the years, other clusters showed the same problem. The problem of a “missing mass” was born because the mass possessed by clusters was too less compared to their velocity and the escape velocities should have exceeded in these clusters. This “missing mass” is indeed dark matter.
The problem of “dark matter” came back in 1976. In 1976, another astrophysicist – Vera Rubin – discovered that this problem of “missing mass” was not limited to clusters. It existed in galaxies like Milky Way too. Within the visible disk of each galaxy, the more the distance of a star from the centre of a galaxy, more is its speed. This enables higher orbital speed as there is more mass between stars (that are far away from the centre of the galaxy) and the centre of the galaxy.
Beyond the galaxy’s disk, one can still find isolated gas clouds (like the Small Magellanic Clouds). Rubin discovered that using these objects as references of the exterior of the galaxy’s gravity field (no visible matter adds to total here), their orbital speed remained high. These regions contained too less matter to explain this anomaly.
This leads us to the conclusion that dark matter exists in these regions, well beyond the visible edge of the galaxies. These zones are called as “dark matter haloes”.
Dark matter is not a type of ordinary matter. How do we know this? First, let’s consider whether it resides in black holes. It’s simple – No! These many black holes would have been detected easily from their gravitational effects on nearby celestial objects. Is it a type of dark cloud? No, it would have interacted with light from stars behind it if it were a dark cloud. Is it an interstellar rogue entity like Han Solo? No, the universe could not have manufactured six times as much mass as that of ordinary matter in the universe.
The idea of dark matter being a type of ordinary matter is crushed by our observations about the amount of helium and hydrogen in the universe. Nuclear fusion, during the initial stages of Big Bang, would leave one helium nucleus for every ten hydrogen nuclei. Dark matter’s presence would mean that this ratio would differ significantly and there would be more helium compared to hydrogen. Hence, dark matter does not participate in nuclear fusion, which means it is not ordinary matter.
Cosmic Microwave Background verifies that dark matter and nuclear fusion have no relation. Dark matter, hence, is something mysterious altogether.
Critics might horn their glasses of scrutiny to compare dark matter to “aether” (a hypothetical, weightless, transparent medium allowing light to pass through it), but their glasses will be knocked askew by the fact that unlike aether, dark matter is real. We now know that electromagnetic radiation does not require any medium and so there is no requirement of an aether. Aether was a misconception in the laws of physics; dark matter is a reality. Dark matter is not an assumption but a derivation of observed effects. Dark matter has been fabricated from the concept of reality and observation – dark matter has not been invented.
Physicists are sure that dark matter consists of a class of undiscovered particles, interacting with matter only through gravity. But dark matter is not the only thing: even dark energy exists. To know more about dark energy, look out for the next article. Keep reading!!! And continue to speculate, innovate till you constipate!