The universe could be younger than we think, based on the motions of satellite galaxies that reveal how recently they have fallen into a galaxy grouping.
According to measurements of the cosmic microwave background radiation (CMB) by the European Space Agency‘s Planck mission, the universe is about 13.8 billion years old. This calculation is based on what’s known as the Standard Model of cosmology, which describes a flat universe dominated by dark energy and dark matter and which is expanding at an accelerating rate.
The Standard Model is then used as a basis for supercomputer simulations that can depict the growth of large-scale structure in the universe — galaxies, galaxy clusters and huge chains and walls of galaxies.
However, these models have now run afoul of new measurements of the motions of pairs of galaxies that don’t tally with what the simulations are telling us.
Related: How old is the universe?
In a new study, astronomers led by Guo Qi from the National Astronomical Observatories of the Chinese Academy of Sciences studied pairs of satellites in galaxy groups.
Galaxy groups are small collections of galaxies, such as our own Local Group, in which a few large galaxies are joined by a swarm of smaller ones. Like larger galaxy clusters, these galaxy groups form where filaments in the cosmic web of matter that spans the universe meet, with smaller galaxies moving along the filaments before falling into a group.
Using observations made by the Sloan Digital Sky Survey (SDSS) of 813 galaxy groups within about 600 million light-years from Earth, Qi’s team focused on the most massive galaxy in each group and measured how pairs of satellites on opposite sides of that galaxy moved.
They found that the fraction of satellite galaxies that were counter-rotating with respect to each other — in other words, orbiting the large galaxy in opposite directions — is higher than predicted by computer simulations of large-scale structure, such as the Millennium…