A new measurement of the universe has confirmed that dark energy makes up nearly 69 percent of the totality of everything.
So the remaining 31 percent matter; both the normal variety—that is, the particles and forces that make up everything we can see—and dark matter, the mysterious gravitational poltergeist responsible for movements and effects that cannot currently be explained in any other way.
“Cosmologists believe that only about 20 percent of the total mass is made up of ordinary or ‘baryonic’ matter, which includes stars, galaxies, atoms and life.” explains astronomer Mohamed Abdullah National Research Institute of Astronomy and Geophysics in Egypt and Chiba University in Japan.
“About 80 percent is dark matter, the mysterious nature of which is not yet known, but may consist of some as-yet-undiscovered subatomic particles.”
Dark energy, on the other hand, is more of a force. We I do not know what it is, either. It’s the name we give to whatever is driving the accelerating expansion of the universe, and there’s a lot of it out there. Repeated measurements have found that they make up most of the mass and energy density in the universe in amounts that tend to hover around 70 percent.
So far, the rate at which the universe is expanding has proven to be extremely complex, but there are many good reasons why scientists want it to. Narrowing down the density of matter and energy in the universe could help scientists find out what dark energy ishow it has affected the expansion of the universe so far and what could happen in the future: The universe expands forever, or reverses and shrinks to Big Crunch.
One tried and true way to find out how much dark energy there is relies on galaxy clusters. This is because they are composed of matter that has been gravitationally bound together over the lifetime of the universe, approximately 13.8 billion years.
By comparing the number of galaxies in a cluster and its mass compared to numerical simulations, scientists can calculate the mass-to-energy ratios.
“Because the current galaxy clusters formed from matter that collapsed under its own gravity over billions of years,” explains astronomer Gillian Wilson from the University of California Merced, “the number of currently observed clusters, the so-called ‘cluster abundance’, is very sensitive to cosmological conditions and especially to the total amount of matter”.
But since most of the mass is supplied by dark matter, it is difficult to measure the mass of a cluster of galaxies directly. Instead, the scientists determined the mass of the galaxy clusters in their database, carefully analyzed using GalWeight team technique to ensure that each contains only clusters of galaxies by counting the number of galaxies in each. Because more massive clusters have more galaxies, a relationship known as the relationship between matter and wealth (MMR), the researchers were able to estimate the total mass of each of their sample clusters.
They then ran numerical simulations to create galaxy clusters with variable proportions of dark energy and matter. The simulations that most closely resembled the observed galaxy clusters were of a universe that consisted of 31 percent matter.
This is very close to (and an improvement on) the team’s previous effort, which yielded a proportion of dark energy of 68.5 percent and matter of 31.5 percent. It is also in very good agreement with other measurements of the density of matter and energy in the universe, suggesting that we are very close to determining it.
“We were able to make the first measurement of the mass density using the MRR, which is in excellent agreement with that obtained by the Planck team using cosmic microwave background method,” says astronomer Tomoaki Ishiyama from Chiba University.
“This work further demonstrates that the cluster abundance is a competitive technique for constraining cosmological parameters and complements cluster-free techniques such as CMB anisotropy, baryon acoustic oscillations, Type Ia supernovaeor gravitational lenses.”
The research was published in The Astrophysical Journal.
