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Galaxies’ Motion Implies a Potentially Younger Universe Than Previously Believed

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by Denzel Harber 3 months ago3 months ago

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Galaxies’ Motion Implies a Potentially Younger Universe Than Previously Believed

We think the universe is 13.8 billion years old, but could we be wrong? A new study of bound galaxies offers an unexplored clue.

Based on the movements of satellite galaxies that have recently fallen into a galaxy grouping, it is possible that the universe is younger than previously believed. The age of the universe, estimated to be around 13.8 billion years old, is based on measurements of the cosmic microwave background radiation (CMB) conducted by the European Space Agency’s Planck mission. This calculation is derived from the Standard Model of cosmology, which describes a flat universe dominated by dark energy and dark matter, and expanding at an accelerating rate.

To further understand the growth of large-scale structures in the universe, such as galaxies, galaxy clusters, and chains of galaxies, supercomputer simulations are used based on the Standard Model. However, these simulations are now conflicting with new measurements of galaxy pairs’ motions.

In a recent study led by Guo Qi from the National Astronomical Observatories of the Chinese Academy of Sciences, astronomers examined pairs of satellites within galaxy groups. Galaxy groups are small clusters of galaxies, similar to our own Local Group, where a few large galaxies are accompanied by numerous smaller ones. These groups form at the intersections of filaments in the cosmic web of matter that spans the universe, with smaller galaxies moving along these filaments before eventually joining a group.

Based on the observations conducted by the Sloan Digital Sky Survey (SDSS), Qi’s team focused on studying the movement of pairs of satellites located on opposite sides of the most massive galaxy in each of the 813 galaxy groups within a distance of approximately 600 million light-years from Earth.

Their findings revealed that the proportion of satellite galaxies that exhibited counter-rotating motion, meaning they orbited the large galaxy in opposite directions, was higher than what computer simulations of large-scale structure, such as the Millennium Simulation and the Illustris TNG300 model, predicted. These simulations are based on the Standard Model as described by the Planck mission.

Typically, when satellites have recently fallen into orbit around a larger galaxy in a group, this counter-rotating motion is expected. However, as time progresses, galaxy groups and clusters should reach a state of dynamic relaxation, where most satellites co-rotate. If galaxy groups and clusters formed as the Standard Model suggests, then the fraction of counter-rotating satellites should be smaller. The fact that they make up a larger fraction of satellites poses a challenge to the Standard Model.

An example of a galaxy group, in this case the Copeland Septet. Do the motions of smaller satellite galaxies in such groups imply that the universe is younger than we think? (Image credit: DESI Legacy Imaging Surveys/LBNL/DOE & KPNO/CTIO/NOIRLab/NSF/AURA)

According to Qi, the SDSS data indicates that satellite galaxies are currently in the process of accreting or falling into the massive groups, displaying a stronger signal of ongoing assembly compared to simulations based on Planck parameters. This suggests that the satellite galaxies have recently fallen into their respective groups.

As a result, it implies that the age of the universe may be younger than what the Planck observations of the Cosmic Microwave Background (CMB) suggest. However, Qi notes that this study cannot provide a quantitative estimation of the universe’s age due to the significant variability in the motions of satellite pairs and the models used to understand the formation of galaxy groups. Therefore, it is challenging to determine precisely how much younger than 13.8 billion years these results imply the universe to be.

If accurate, the recent discoveries suggest that there may be discrepancies in the Standard Model, indicating that some of our assumptions about the universe are incorrect. In fact, scientists are currently investigating a cosmic paradox that could potentially provide an explanation.

The rate at which the universe is expanding is determined by a value known as the Hubble constant. According to Planck’s measurements, the Hubble constant is 67.8 kilometers per second per megaparsec. This means that every megaparsec of space is expanding by 67.8 kilometers (42.1 miles) every second. By rewinding the clock based on this expansion rate, cosmologists have calculated the age of the universe to be 13.8 billion years.

However, observations of the redshift of Type Ia supernovae, which are exploding white dwarfs, indicate a different value for the Hubble constant – 73.2 kilometers (45.5 miles) per second per megaparsec. Rewinding the clock using this expansion rate would result in a younger age for the universe, approximately 12.6 billion years.

Both measurements of the Hubble constant are considered to be highly reliable, yet they significantly diverge. This discrepancy is commonly referred to as the “Hubble tension.”

When asked about the implications of the younger age suggested by satellite pairs in galaxy groups, Qi acknowledged that it could potentially be connected to the Hubble tension problem caused by the faster rate of expansion indicated by the supernova measurements.

However, there are additional challenges to address. If we decrease the age of the universe too much, astronomers would find themselves in the peculiar situation of having stars that are known to be older than the universe itself.

Perhaps the explanation lies within other aspects of the Standard Model. For instance, the model heavily relies on dark matter, but scientists are still unaware of what dark matter truly is. Some researchers argue that dark matter doesn’t exist at all, and instead propose that its gravitational effects can be explained by modifying the laws of gravity at low accelerations, such as those experienced by satellite galaxies orbiting at greater distances. Qi’s team discovered that satellite pairs at larger orbital radii are more likely to be counter-rotating.

At present, additional data would be greatly appreciated. Qi mentioned that the same phenomenon should apply to larger galaxy clusters as well, but these clusters are typically located farther away. The limited sample size and lower quality of current data render any measurement inconclusive.

Regardless of the correct age value, the universe is ancient, but these new findings suggest that it may be able to regain some of its youthful characteristics.

The recent discoveries were published on Jan. 22 in the journal Nature Astronomy.

This article is republished from livescience under a Creative Commons license. Read the original article.

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