What is dark matter? Today astrophysicists know that the universe is made up of approximately 25% dark matter, and another 70% dark energy. Dark matter does not emit light and therefore we cannot detect it; but, in fact, it exists.
And if it exists and cannot be seen, how do we know it is there? Javier Santaolalla, engineer and doctor in Particle Physics, gives us a metaphor so that we can understand it.
“As if we shake a pizza box we know that there is something inside it, because of its weight, the same happens with galaxies.”
This is what has been done with the galaxies, they have been weighed and it is perceived that there is something inside. But this is not seen: dark matter does not emit visible light or any other radiation.
And how is a galaxy “weighed”? Because of the gravitational effects that dark matter exerts on the rotation curve of galaxies, scientists can deduce that it is there.
It is intriguing to be certain that most of the matter in the universe cannot be perceived, and scientists are already raising various possibilities about the composition of dark matter.
Specifically, astronomers consider four possibilities: that dark matter is made up of neutrinos, subatomic particles without electric charge or mass; from WIMPs, weakly interacting massive particles; of MACHOs, huge low-mass planets or white dwarf stars, and of black holes.
In fact, one of the hypotheses is that all the galaxies in the universe exist within a large cluster of dark matter.
Although there have been many attempts at direct observation, all of them have been unsuccessful. Many scientists say they have provided apparent evidence of the existence of dark matter in the universe, such as the speed at which galaxies rotate, the gravitational lensing of background objects or how the temperature of hot gas is distributed throughout the galaxies. However, these “clues” are not direct observations, so they cannot be called direct detections.
Therefore, it is one of the greatest mysteries in the universe and, at the same time, an incredible challenge for modern science.
One of the great achievements of 21st century science, according to the most optimistic omens, will be the detection, at last, of dark matter, and its identification beyond doubt.
