How much “stuff” is there in the universe? You’d think it would be easy to figure that out. But it is not. Astronomers add what they can discover, and still find that there is more to the universe than they see. So, what is “there” and how do they explain it all?
According to astronomer Mohamed Abdullah (National Research Institute for Astronomy and Geophysics in Egypt and Chiba University (Japan)), the universe contains both dark and visible components. Matter makes up only 31% of the known universe. The rest is dark energy, which is still largely unknown. “Cosmologists believe that only about 20% of this total matter consists of ordinary or ‘baryonic’ matter, which includes stars, galaxies, atoms and life,” he said. “about 80%” [of all matter] It is made of dark matter, the mysterious nature of which is not yet known, but may consist of some subatomic particles that have not yet been discovered.
Determine the composition of the universe using galaxy groups
The best measurements of the “stuff of the universe” come from the Planck satellite, which has mapped the universe. He studied the cosmic microwave background, the radiation left over from the Big Bang, about 13.8 billion years ago. Planck’s measurements allowed astronomers to arrive at the “gold standard” measurements of the total matter in the universe. However, it is always a good idea to verify Planck using other methods.
Abdullah and a team of scientists did just that. They used another method called cluster richness relationship. It basically measures the number of galaxy members in a cluster to determine the cluster’s mass. According to astronomer and team member Gillian Wilson, it provides a way to measure cosmic matter. “Because current galaxy clusters were formed from matter that collapsed over billions of years under the influence of their own gravity, the number of clusters observed at present, or the so-called ‘cluster abundance’, is very sensitive to cosmic conditions,” she said. “In particular, the total amount of matter.” “, noting that the method compares the observed number and mass of galaxies per unit volume with predictions from numerical simulations.
It is not an easy method because it is difficult to accurately measure the mass of any galaxy cluster. Much of the cluster’s mass is dark matter. In other words, what you see in the set is not necessarily all you get. So, the team had to get smart. They used the fact that more massive clusters contain more galaxies than less massive galaxies. Since all galaxies contain bright stars, the number of galaxies in each group is used to estimate the total mass. Essentially, the team measured the number of galaxies in each cluster in their sample and then used that information to estimate the total mass of each cluster.
Planck matching
The result of all measurements and simulations roughly matches the Planck numbers for mass in the universe. They found a universe composed of 31% matter and 69% dark energy. It also appears to agree with other work the team has done to measure galaxy masses. To obtain their results, Mohammed’s team was able to use spectroscopic studies of the clusters to determine their distances. The observations also allowed them to know which galaxies belong to specific groups.
Simulations were crucial to this work as well. Observations made by the Sloan Digital Sky Survey allowed the team to compile a catalog of galaxy clusters called “GalWeight.” They then compared the collections in the catalog to their simulations. The result was a calculation of the total matter in the universe based on the mass-richness relationship.
This technology is powerful enough to be used when new astronomical data arrives from different instruments. According to Wilson, the team’s work shows that MRR technology extends beyond their work. “MRR technology can be applied to new data sets that are becoming available from wide-field and deep imaging and spectroscopic surveys of galaxies such as the Dark Energy Survey, the Dark Energy Spectroscopic Instrument, the Euclid Telescope, the eROSITA telescope, and the James Webb Space Telescope.” He said.
The results also show that mass abundance is a competitive technique for constraining cosmological parameters. It complements non-group-focused techniques as well. These include CMB anisotropy, baryonic acoustic oscillations, type Ia supernovae, or gravitational lensing. Each of these is also a useful tool for measuring different properties of the universe.
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Researchers have shown that most of the universe consists of dark energy
Constraining cosmological parameters using the cluster-mass richness relation
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