The universe could be younger than we think, based on the movements of satellite galaxies that reveal how recently they have fallen into a galaxy cluster.
Based on cosmic microwave background (CMB) measurements by the European Space AgencyAccording to the Planck mission, the universe is about 13.8 billion years old. This calculation is based on what is known as the Standard Model of cosmology, which describes a flat universe dominated by dark energy and dark matter and that it is expanding at an accelerated rate.
The standard model is then used as a basis for supercomputer simulations that can represent the growth of large scale structure in the universe — galaxies, galaxy clusters, and huge chains and walls of galaxies.
However, these models have now conflicted with new measurements of the movements of pairs of galaxies That doesn’t match what the simulations tell us.
In a new study, astronomers led by Guo Qi of the National Astronomical Observatories of the Chinese Academy of Sciences studied pairs of satellites in galaxy groups.
Galaxy groups are small collections of galaxies, like our own Local Group, in which a few large galaxies are joined by a swarm of smaller galaxies. Like larger galaxy clusters, these galaxy groups form where the filaments of the cosmic web of matter that spans the universe meet, and smaller galaxies move along the filaments before falling into a cluster.
Using observations by the Sloan Digital Sky Survey (SDSS) of 813 galaxy groups about 600 million light years away LandQi’s team focused on the most massive galaxy in each group and measured how pairs of satellites on opposite sides of that galaxy they moved.
They found that the fraction of satellite galaxies that rotated away from each other (in other words, orbited the large galaxy in opposite directions) is larger than predicted by computer simulations of large-scale structures, such as the Millennium Simulation and the Illustris model. TNG300, both based on the standard model described by the Planck mission.
This is a natural situation if the satellites have just entered orbit around the largest galaxy in the group. But over time, galaxy groups and clusters should reach a dynamically relaxed state, in which most satellites co-rotate. If galaxy groups and clusters merged when the Standard Model suggests they should, then the fraction of counter-rotating satellites should be smaller. The fact that they are a larger fraction of satellites is a problem for the Standard Model.
“We found in the SDSS data that satellite galaxies are simply accreting or falling into massive groups, with a stronger signal of ongoing assembly compared to simulations with Planck parameters,” Qi told Space.com in an email. .
In other words, it appears that the satellite galaxies have recently fallen into their respective groups.
“This suggests that the universe is younger than Planck’s CMB observations suggest,” Qi said. “Unfortunately, this work cannot estimate the age of the universe quantitatively.”
This is because there is still too much wiggle room in the movements of the satellite pairs and in the models of how the clusters form to be able to put a firm figure on how much younger than the 13.8 billion years that these results suggest it will be. It is the universe.
If they are correct, then the new findings imply that something is wrong with the Standard Model and that some of our assumptions about the universe must be wrong. In fact, a cosmic paradox that scientists are currently investigating could be the answer.
The expansion rate of the universe is defined by a number called the Hubble constant. Planck measured the Hubble constant at 67.8 kilometers per second per megaparsec; In other words, each megaparsec volume of space It is expanding 67.8 kilometers (42.1 miles) per second. (One megaparsec is approximately equivalent to (3.26 million light years). Based on this expansion rate, cosmologists can estimate the age of the universe to be 13.8 billion years by turning back the clock.
However, observations of the redshift of type Ia supernovae, which are exploding white dwarfs, give a value for the Hubble constant of 73.2 kilometers (45.5 mi) per second per megaparsec. At this expansion rate, turning back the clock would give a younger age, 12.6 billion years.
Both measurements of the Hubble constant are considered impeccable, and yet they differ dramatically. This paradox is known as the “Hubble tension.”
“This, of course, could be related to the Hubble strain problem,” Qi said when asked whether the younger age suggested by satellite pairs in the galaxy groups supports a faster expansion rate from supernova measurements.
However, there are other obstacles to overcome. If we reduce the age of the universe too much, astronomers will find themselves in the awkward position of having to stars which are known to be older than the universe itself.
Perhaps the explanation lies in other aspects of the Standard Model. For example, the model relies heavily on dark matter, but so far scientists do not know what dark matter is. Other researchers maintain that dark matter does not exist at all and that its gravitational effects can be explained by a modification of the laws of gravity at low accelerations, such as those experienced by satellite galaxies orbiting at greater distances. Qi’s team found that pairs of satellites with larger orbital radii are more likely to be in counter-rotation.
At this point, more data would be welcome. The same phenomenon should apply to larger galaxy clusters, Qi said, but the clusters tend to be farther away and the limited sample size and poorer data quality currently make any measurements inconclusive.
The universe is old, whatever the correct age value is, but these new results suggest that it may regain some of its youth.
The new findings were published January 22 in the journal Nature Astronomy.
Originally published in space.com.