Fritz Zwicky, the legendary Swiss astrophysicist, was the first one to ever propose the existence of dark matter, by calculating the velocity of galaxies in the Coma Cluster (A cluster 321M light-years apart from us). He found that more matter would be required to keep the cluster together, and not “fly away”, due to the high speed of those galaxies.
In his calculations, there was about 400 times more mass than the observed one (stars, planets,…) in that cluster. So he guessed the presence of “Dunkle Materie” (dark mater in English), invisible to the telescope but whose gravitational effect held the cluster together. Zwicky’s prediction wasn’t taken seriously until decades later.
The hunt for dark matter only started in the 1970s when Vera Rubin discovered that the rotation of spiral galaxies was too fast given their mass invisible matter. If the galaxies only had normal matter in within them, the galaxy couldn’t have been formed in the first place. Either was General Relativity wrong or some kind of “invisible” matter was present in galaxies. It’s more likely that there is “something” out there because we see something called gravitational lensing. Gravitational lensing is the curvature of space caused by massive objects (such as big agglomerations of dark matter, or galaxies clusters) which lets you see objects that are behind that object.
Read Also: Dark Matter – A Secret of The Universe
After all these years we are pretty sure what dark matter is not. It’s not the dust of normal matter, because we would see it with normal telescopes. It’s not antimatter, sense when normal matter and antimatter collide it produces very specific gamma rays. And lastly, it’s not black holes because the dark matter seems to be permeating all of space and not single spots.
Physicists thought that with this additional mass (about 85% of all matter in the Universe) the Universe would re-collapse on itself in the future. But there was something else…
In 1998 two independent teams of astronomers (Supernovae Cosmology Project and High-Z Supernovae Search Team) tried to calculate the evolution of the expansion of the Universe by looking at something called Type one-A supernovae. This kind of supernovae is called a “Standard Candle” because of its expected brightness. By knowing the supernovae brightness the team just needed to see how fainter the supernovae looked and calculate its distance.
The result they obtained was quite surprising: The Universe expansion was accelerating over time. This was the last thing they expected because theoretically there was nothing propelling it. It’s here that the Cosmological Constant (or big Lambda) comes in. The once called Einstein’s biggest blunder was actually right!
In Einstein’s General Relativity equations he added something called the Cosmological constant. This “force” would counteract the force of gravity and make the Universe static. This force would also have a really weird property: its density stays the same all over space and time. This would mean that dark energy is a property of space-time itself. So as the Universe expands there is more and more dark energy. The universe will accelerate forever (probably)!
End of the Universe: Heat Death
In this model (Lambda-CDM model) the universe will end in “heat death” in which the galaxies will be farther and farther apart. The stars will die and their production will end. Then the white dwarfs will disappear and even neutron stars will faint away. And if Hawking radiation does occur (which probably does) even the mighty Black holes will disappear and Universe will be dark and cold forever. Still, it will take a long long time until this happens.