The universe could be younger than we think, based on the movements of satellite galaxies that reveal how recently they fell into a group of galaxies.
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 is known as the Standard Model cosmologywhich describes a flat universe dominated by dark energy And dark matter and which is expanding at an increasingly rapid pace.
The Standard model is then used as the basis for supercomputer simulations that can represent the growth of large-scale structures in the world the universe – galaxies, clusters of galaxies and huge chains and walls of galaxies.
However, these models have now collided with new measurements of pairs’ movements galaxies that doesn’t match what the simulations tell us.
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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 groups of galaxies.
Groups of galaxies are small collections of galaxies, like our own Local Group, in which a few large galaxies are joined by a swarm of smaller ones. Like larger clusters of galaxies, these groups form galaxies where filaments in the cosmic web matter spanning 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 groups of galaxies within approximately 600 million light years by SoilQi’s team focused on the most massive galaxy in each group and measured how it mated satellites moved on either side of that galaxy.
They found that the fraction of satellite galaxies that rotated oppositely to each other – in other words, orbited the large galaxy in opposite directions – is higher than predicted by computer simulations with large-scale structures, such as the Millennium Simulation and the Illustris TNG300 model, which both are based on the standard model as described by the Planck mission.
This is a natural thing to do when the satellites have just entered orbit around the group’s larger galaxy. But over timegroups and clusters of galaxies should reach a dynamically relaxed state, with most satellites co-rotating. If groups and clusters of galaxies merge as the Standard Model suggests they should, then the fraction of counter-rotating satellites should be smaller. The fact that they make up a larger share of satellites is a problem for the standard model.
“We found from the SDSS data that satellite galaxies are actually growing in 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 only recently fallen into their respective groups.
“This suggests that the universe is younger than the Planck observations from the CMB suggest,” Qi says. “Unfortunately, this work cannot quantitatively estimate the age of the universe.”
This is because there is still too much wiggle room in the movements of the satellite pairs and models of how groups form to give a definitive figure on how much younger than 13.8 billion years these results suggest the universe is.
If correct, 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, one cosmic paradox scientists are currently investigating could be the answer.
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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 room expanding by 67.8 kilometers (42.1 miles) every second. (One megaparsec is approximately (3.26 million light years).) Based on this expansion rate, cosmologists can calculate the age of the universe to be 13.8 billion years by turning back the clock.
However, observations of the redshift of Type Ia supernovasthat explode white dwarfsGive the value of the Hubble constant as 73.2 kilometers (45.5 miles) per second per megaparsec. At this rate of expansion, turning back the clock would give us a younger age of 12.6 billion years.
Both measurements of the Hubble constant are considered indisputable, yet they differ drastically. This paradox has become known as the ‘Hubble tension.”
“This could of course be related to the Hubble tension problem,” Qi said when asked whether the younger age suggested by satellite pairs in galaxy groups provides support for the faster expansion rate of the supernova measurements.
However, there are other obstacles to overcome. If we lower the age of the universe too much, astronomers will find themselves in a difficult position stars that they are known to be older than the universe itself.
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Perhaps the explanation lies in other aspects of the Standard Model. For example, the model relies heavily on dark matter, but scientists don’t know what dark matter is so far. Other researchers claim that dark matter does not exist at all and that its gravitational effects can be explained by: changing the laws of gravity at low accelerations, such as those experienced by satellite galaxies orbiting the Earth at greater distances. Qi’s team found that satellite pairs with larger orbital radii are more likely to rotate in opposite directions.
More data would be welcome at this point. The same phenomenon should apply to larger clusters of galaxies, Qi said, but clusters tend to be further away and limited sample sizes and poorer data quality currently make any measurement inconclusive.
The universe is old, regardless of which age value is correct, but these new results suggest it may be regaining some of its youth.
The new findings were published in the journal on January 22 Nature Astronomy.