The amount of matters that makes up the entire universe can be tricky to measure. What is known is the fact that the most of the universe’s matter-energy density consists of three forces the first is dark energy, which is the unknown force driving the universe farther apart from within itself making it expand sporadically then the other two being dark matter, both normal and dark.
But in order to be accurate about figuring out the proportions of these three can be a challenge but scientific researchers claimed to have performed one of the most precise measurements in order to determine the proportion of matter.
Based on their calculations, normal matter and dark matter combined together makes up about 31.5% of the matter-energy density of the universe while the remaining dark energy makes the majority which is 68.5%.
“To put that amount of matter in context, if all the matter in the universe were spread out evenly across space, it would correspond to an average mass density equal to only about six hydrogen atoms per cubic meter,” said astronomer Mohamed Abdullah of the University of California, Riverside and the National Research Institute of Astronomy and Geophysics in Egypt.
“However, since we know 80 percent of matter is actually dark matter, in reality, most of this matter consists not of hydrogen atoms but rather of a type of matter which cosmologists don’t yet understand.”
The need to better understand dark energy is really important in order to get a better glimpse of the Universe itself. One thing unknown is the “Dark” in the name refers to that mystery – but what is known is that this is being linked to the force that drives the Universe’s expansion, the velocity of which has proven incredibly difficult to narrow down past a certain point.
When there is a clearer understanding of the expansion rate, this will further improve our understanding of the Universe as a whole as well as its evolution. Hence, constraining the properties of dark energy is a pretty important undertaking for cosmology in general, and there are a number of ways to do so.
A team of researchers led by Abdullah used a method that is based on how things move around in galaxy clusters – groups of up to thousands of galaxies gravitationally bound together.
Galaxy clusters have proven to being one of the best tools for measuring matter in the Universe because they’re made up of matter that has come together over the lifetime of the Universe which is about 13.8 billion years under gravity.
The number of clusters we can observe in a volume of space is highly sensitive to the amount of matter, so counting them can give a reasonable measurement. But, again, that’s not a simple task.
“A higher percentage of matter would result in more clusters,” Abdullah said.
“The ‘Goldilocks’ challenge for our team was to measure the number of clusters and then determine which answer was ‘just right’. But it is difficult to measure the mass of any galaxy cluster accurately because most of the matter is dark so we can’t see it with telescopes.”
The team were able to bypass the issue with a technique called GalWeight. This is done by using the orbits of galaxies in and around a cluster to determine which galaxies actually belong to any given cluster or which doesn’t belong with more than 98% accuracy.
This according to the researchers provides a much more accurate census of that given cluster, in turn leading to a much more accurate mass calculation.
“A huge advantage of using our GalWeight galaxy orbit technique was that our team was able to determine a mass for each cluster individually rather than rely on more indirect, statistical methods,” explained astronomer Anatoly Klypin of New Mexico State University.
Other things the researchers did was applying a technique to observations collected by the Sloan Digital Sky Survey, and then created a catalogue of galaxy clusters which were then compared to numerical simulations of galaxies in order to calculate the amount of matter in the Universe.
The team’s result – 31.5 percent matter and 68.5 percent dark energy – is in close agreement with other measurements of the Universe’s matter-energy density.
“We have succeeded in making one of the most precise measurements ever made using the galaxy cluster technique,” said astronomer Gillian Wilson of UC Riverside.
“Moreover, this is the first use of the galaxy orbit technique which has obtained a value in agreement with those obtained by teams who used noncluster techniques such as cosmic microwave background anisotropies, baryon acoustic oscillations, Type Ia supernovae, or gravitational lensing.”
This result demonstrates that GalWeight could prove to be a very useful tool for continuing to probe as well as constrain the cosmological properties of the Universe.
