Scientists have now estimated the total amount of matter in the universe, using a new, more precise method. By calculating the mass of hundreds of galaxy clusters, the team found that matter makes up less than a third of the contents of the universe.
Everything we see around us and interact with in our everyday lives actually only makes up a tiny fraction of what’s in the cosmos. It’s long been understood that there’s a roughly 32/68 split between matter and energy, and even within that minority of matter, most of it is “dark”. Regular (or baryonic) matter only accounts for around five percent of everything.
The new calculation, conducted by a team of scientists led by the University of California, Riverside, fine tunes that ever so slightly. According to the study, matter makes up about 31.5 percent of the total contents of the universe. The remaining 68.5 percent is dark energy, a mysterious force that seems to be driving the acceleration of the expansion of the universe.
“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,” says Mohamed Abdullah, first author of the study. “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.”
To reach their conclusion, the researchers developed a new tool called GalWeight, which allows them to calculate the mass of a cluster of galaxies by measuring the orbits of the individual galaxies. Applying this to 756 clusters in data from the Sloan Digital Sky Survey, the team can then compare the results to simulations of how galaxy clusters form. Those simulations start with different amounts of matter, so by seeing which simulated conditions most closely match the observations, they can determine the most likely amount of matter the universe contains.
“We have succeeded in making one of the most precise measurements ever made using the galaxy cluster technique,” says Gillian Wilson, co-author of the study. “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.”
While this information might not matter (pun intended) to most people, understanding the evolution of the universe could eventually help us finally uncover the mysteries of dark matter and dark energy.
The research was published in the Astrophysical Journal.
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