Our Expanding Galaxy: The Mystery Explained

For those of you who are sci-fi movie fans, have ever watched or heard of the Star Trek series (I, for one, am currently on season 3 of Star Trek Discovery on Netflix…. would strongly recommend) or are generally interested in astronomy, you may have come across the terms ‘dark matter’ and ‘dark energy’. At first, this sounds like a way of describing evil or enigmatic atmospheres, however, these concepts have been floating around for the last few decades and have left many scientists wondering what the makeup of our universe actually is.


The universe is full of matter and the attractive force of gravity pulls all matters together. Billions of years ago, the universe was expanding more slowly than it is today. This was shown by Edwin Hubble, an American astronomer, who played a crucial role in the field of observational cosmology whose law states that the further away the perimeter of the galaxy is from the Earth, the faster its recessional velocity.
Dark energy is a type of energy that permeates the whole universe and opposes the attractive force of gravitation between galaxies by the exertion of negative pressure. It is not detected directly but we know it exists because we now know the universe is accelerating as it expands. In the early 1990s, astronomers were observing the expansion of the universe as they tried to determine the rate at which its acceleration was decreasing.

Dark matter is a matter which cannot be seen and that does not admit or absorb electromagnetic radiation. It is detected indirectly based on its gravitational effects relating to either the rotation of galaxies or by gravitational lensing of starlight. Like dark energy, scientists believe that dark matter exists, but they do not know what it is or where it has come from. After the Big Bang, hydrogen and helium were present in the universe and they agree with the present levels of hydrogen and helium in the universe. This suggests that the missing mass of the universe is not likely to be made up of normal matter, which is made from protons and neutrons and is described as baryonic matter. It has been said that dark matter may be made over a new particle which was created in The Big Bang but has not been detected.


According to NASA, roughly 68% of the universe is dark energy and 27% is dark matter, which means that the remaining 5% is everything on Earth which is referred to ‘ordinary’ or ‘normal’ matter. At present, astronomers do not know what dark matter and dark energy are, and this remains one of the key outstanding areas of physics that are awaiting further evidence, understanding and clarification.


There are currently three different explanations for dark energy. The first explanation is that dark energy is a property of space meaning that it would be unchanged as the universe expands. So as more space comes into existence, more of this dark energy would come about. This would result in the universe to expand faster. The second explanation is that space has energy coming from the quantum theory of matter. Here, the theory suggests that space in the universe is full of temporary particles that form and disappear in short spaces of time. The third explanation for dark energy is that there is a new form of energy whose effect on the expansion of the universe is the complete opposite to what the matter and normal energy that we know of does. For all three explanations, scientists are struggling to come up with evidence to back up their theories.


According to CERN, the European Organization for Nuclear Research, dark matter seems to outweigh visible matter roughly six to one, making up about 27% of the universe. Most scientists think that dark matter is composed of non-baryonic matter. But the explanations we have, for both dark matter and dark energy, still leave scientists clueless as to why the strange force exists in the first place and makes us realise that there is still so much that we do not know about our vast universe.

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