We see countless stars and galaxies twinkling in the universe today, but how much matter is actually there? The question is simple enough, but the answer seems surprising.
This dilemma exists largely because current cosmological observations simply disagree about how matter is distributed in the current universe.
A new computer simulation that tracks how all the elements of the universe — ordinary matter, dark matter, and dark energy — evolve according to the laws of physics would be useful. The stunning images show the galaxies and clusters of galaxies visible in the image Universeis fed by what is called The cosmic web. This network is The largest structure in the universebuilt of filaments composed of ordinary matter, or baryonic matter, and Dark matter.
Unlike previous simulations that looked only at dark matter, the new work, carried out by a project called FLAMINGO (short for Full-Scale Large-Scale Structure Simulation with All-Sky Mapping to Interpret Next Generation Observations), also tracks regular matter.
Related: Are we living in a simulation? The problem with this mind-boggling hypothesis.
“Although dark matter dominates gravity, the contribution of ordinary matter can no longer be neglected,” Jupp Shaye, a professor at Leiden University in the Netherlands and co-author of the three new studies on the Flamingo project, said in an article. statement.
As for how much matter the universe actually contains, astronomers say computer simulations like these are not just cool cosmic eye candy but also important investigations to help determine the cause of a major discrepancy in cosmology called the “S8 tension.” This is the ongoing debate about how matter is distributed in the universe.
What is S8 tension?
When exploring the universe, astronomers sometimes work with what is known as the S8 parameter. This parameter essentially describes how “clumped” or tightly packed all the matter in our universe is, and can be precisely measured using what are known as low-redshift observations. It is used by astronomers Redshift To measure how far an object is Landand low redshift studies such as “weak Gravitational lens “Surveys” could shed light on processes unfolding in the distant, and therefore older, universe.
But the value of S8 can also be predicted using a function Standard form Cosmology. Scientists can essentially adjust the model to fit the known properties of the object Cosmic microwave background (CMB), which is the residual radiation from the Big Bang, and calculate the clumping of matter from there.
So, here’s the thing.
CMB experiments found a higher S8 value than weak gravitational lensing surveys. Cosmologists don’t know why. They call this contradiction the S8 tension.
In fact, S8 tension is a brewing crisis in cosmology that’s little different from its famous cousin: Hubble tensionWhich refers to the contradictions that scientists face in determining the expansion rate of the universe.
The reason the team’s new simulation doesn’t provide an answer to the S8 jitter problem is a big deal, because unlike previous simulations that only took into account the effects of dark matter on the evolving universe, the latest work takes into account the effects of ordinary matter as well. In contrast to dark matter, it is governed by ordinary matter gravity As well as the pressure generated by gas throughout the universe. For example, driven by galactic winds Supernova Eruptions and actively accumulating Supermassive black holes They are crucial processes that redistribute ordinary matter by blowing its particles into galaxies space.
However, even studying the new work of ordinary matter as well as some of the more extreme galactic winds has not been sufficient to explain the weak clumping of matter observed in the present universe.
“I’m here at a loss,” Shay told Space.com. “An exciting possibility is that the tension points to flaws in the Standard Model of cosmology, or even the Standard Model of physics.”
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Strange physics or a flawed model?
So, where did this S8 tension originate?
“We don’t know what makes this so exciting,” Ian McCarthy, a theoretical astrophysicist at Liverpool John Morris University in the UK and co-author of three new studies, told Space.com.
However, computer simulations, such as those conducted by FLAMINGO, can bring us one step closer. It may help reveal the reason for S8’s jitters because a hypothetical grand map of the universe may help identify potential errors in our current measurements. For example, astronomers are slowly ruling out more mundane explanations for the issue, such as the fact that it might be due to general uncertainty in observations of large-scale structures or related to a problem in the CMB itself.
In fact, the team expects that the effects of natural matter may be much stronger than in current simulations. However, this also seems unlikely, as the simulations agree well with the observed properties of galaxies and galaxy clusters.
“All of these possibilities are very exciting and have important implications for fundamental physics and cosmology,” McCarthy said. But the most interesting possibility is that “the Standard Model is incorrect in some way.”
For example, dark matter could have strange, self-interacting properties not taken into account in the Standard Model, and the S8 jitter could indicate a collapse of our theory of gravity on larger scales, McCarthy said.
However, while the latest simulations track the effects of natural matter and subatomic particles known as… Neutrinos – Both of which were found to be important for making accurate predictions about how galaxies have evolved over the ages – but they did not solve the S8 tension problem.
Here’s the surprising thing: At low redshifts, the universe is noticeably less clumpy than predicted by the Standard Model. But measurements that probe the structures of the universe between The CMB and low redshift measurements “are fully consistent with standard model predictions,” McCarthy said. “The universe appears to have behaved as expected for much of cosmic history, but this changed later in cosmic history.”
Perhaps the key to resolving the S8 tension lies in answering what exactly prompted this change.
This research is described in three Leaves Published in the Monthly Notices of the Royal Astronomical Society.