Scientists, including David Benisty from the Leibniz Institute for Astrophysics Potsdam(AIP), have studied the Centaurus A and M81 galaxy groups to measure their masses and better estimate the Hubble constant.
For decades, astronomers believed they had a good idea of how fast the Universe is expanding. But new research suggests something surprising. The part of the Universe closest to us may actually be expanding more slowly than scientists previously thought.
Using a new method that studies how nearby galaxies move within their cosmic neighborhoods, researchers have found results that could help solve one of the biggest puzzles in modern astronomy, the “Hubble tension.”
The expansion of the Universe is described by the Hubble constant. This number tells scientists how fast galaxies move apart as space expands.
It is usually measured in kilometers per second per megaparsec, meaning how fast a galaxy appears to move away for every 3.3 million light-years of distance.
For years, astronomers have determined this value using two primary methods. One approach involves observing the early Universe through the Cosmic Microwave Background, which provides a snapshot of the Universe shortly after the Big Bang.
The other method relies on measuring distant exploding stars, known as supernovae, in nearby galaxies, allowing scientists to track the expansion rate of the Universe over time.
Both techniques aim to quantify the same fundamental property, though they use very different observational data and physical principles.
But these two methods produce slightly different answers. One suggests the Universe expands at about 68 km/s/Mpc, while the other estimates 73 km/s/Mpc.
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This mismatch, known as the Hubble tension, has puzzled scientists for years.
Instead of studying distant explosions or ancient radiation, researchers tried something different. They analyzed the motion of galaxies inside nearby galaxy groups. These groups exist in a delicate balance.
Gravity pulls the galaxies toward each other, keeping them together. At the same time, the expansion of the Universe slowly pulls the outer galaxies away.
By studying this cosmic tug-of-war, scientists can estimate both the mass of the galaxy group and the rate of cosmic expansion.
The researchers concentrated their study on two nearby galaxy groups: the Centaurus A Group and the M81 Group.
These groups are relatively close to our own cosmic neighborhood. It makes them excellent laboratories for studying how galaxies move under the combined influence of gravity and cosmic expansion.
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By analyzing their motion, scientists calculated a new estimate for the Hubble constant. Their measurement suggested a value of around 64 km/s/Mpc, which is slower than many previous estimates.
If these results hold true, they could help explain part of the Hubble tension. The discrepancy between measurements may not be due to new physics, as some theories suggest.
Instead, it could be related to the methods scientists use to measure cosmic expansion.
By looking at galaxy group dynamics rather than stellar explosions, researchers may be capturing a more complete picture of how the Universe expands locally.
The study also revealed another surprising result. Astronomers often assume galaxy groups are surrounded by large halos of Dark Matter.
But when scientists analyzed the two galaxy groups, they found something unexpected. The visible galaxies themselves appeared to account for most of the group’s total mass.
In other words, less dark matter may be needed to explain their behavior than previously believed. This finding could have major implications for how scientists understand the structure of galaxies.
The researchers believe this new method could open a fresh path for studying the Universe.
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By applying the same technique to larger regions of space, scientists may gain a clearer picture of how galaxies interact with cosmic expansion.
Future observations with powerful telescopes, such as 4MOST, could yield much larger datasets. With more data, astronomers hope to answer two major questions: What is the true expansion rate of the Universe? And how much dark matter really exists?
Knowing how fast the Universe expands is a fundamental question in cosmology. It helps scientists estimate the age of the Universe, understand the evolution of galaxies, and study the nature of dark matter and dark energy.
If the expansion rate is different from previous estimates, it could change our view of the cosmos. In a Universe full of mysteries, some of the biggest discoveries may begin right in our cosmic backyard.
