We see countless stars and galaxies sparkling within the universe today, but how much matter is definitely there? The query is straightforward enough — its answer, nevertheless, is popping out to be quite a head-scratcher.
This dilemma exists largely because current cosmological observations simply disagree on how matter is distributed within the present-day universe.
Of some help may very well be a brand new computer simulation that traces how all elements of the universe — odd matter, dark matter and dark energy — evolve based on the laws of physics. The breathtaking visuals virtually show galaxies, and clusters of galaxies, manifesting in the universe, fed by the so-called cosmic web. This web is the largest structure within the universe, built with filaments made up of each normal matter, or baryonic matter, and dark matter.
Unlike previous simulations that only considered dark matter, the brand new work, carried out by a project called FLAMINGO (short for Full-hydro Large-scale structure simulations with All-sky Mapping for the Interpretation of Next Generation Observations), tracks odd matter too.
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“Although the dark matter dominates gravity, the contribution of odd matter can now not be neglected,” Joop Schaye, a professor at Leiden University within the Netherlands and a co-author of the three latest studies on the FLAMINGO project, said in a statement.
As for the way much matter the universe really incorporates, astronomers say computer simulations like this one are usually not just great cosmic eye candy but additionally essential probes to assist pin down the explanation for a serious discrepancy in cosmology called the “S8 tension.” That is the controversy over how matter within the cosmos is distributed.
What’s the S8 tension?
When investigating the universe, astronomers sometimes work with what’s often called the S8 parameter. This parameter principally characterizes how “lumpy,” or strongly clustered, all of the matter in our universe is, and could be measured precisely with what are often called low-redshift observations. Astronomers use redshift to measure how far an object is from Earth, and low-redshift studies like “weak gravitational lensing surveys” can illuminate processes unfolding within the distant, and subsequently older, universe.
But S8’s value will also be predicted using the standard model of cosmology; scientists can essentially tune the model to match known properties of the cosmic microwave background (CMB), which is the radiation leftover from the Big Bang, and calculate the lumpiness of matter from there.
So, here’s the thing.
Those CMB experiments find a better S8 value than the weak gravitational lensing surveys. And cosmologists do not know why — they call this discrepancy the S8 tension.
In actual fact, S8 tension is a brewing crisis in cosmology barely different from its famous cousin: Hubble tension, which refers back to the inconsistencies scientists face in pinning down the speed of expansion of the universe.
The rationale it’s a giant deal that the team’s latest simulation doesn’t offer a solution to S8 tension is, unlike previous simulations that only considered the consequences of dark matter on an evolving universe, the newest work takes under consideration the consequences of odd matter too. In contrast to dark matter, odd matter is governed by gravity in addition to pressure from gas across the universe. For instance, galactic winds driven by supernova explosions and actively accreting supermassive black holes are crucial processes that redistribute odd matter by blowing its particles out into intergalactic space.
Nevertheless, even the brand new work’s consideration of odd matter in addition to among the most extreme galactic wind was not sufficient to elucidate the weak clumping of matter that’s observed within the present-day universe.
“Here I’m at a loss,” Schaye told Space.com.. “An exciting possibility is that the strain is pointing to shortcomings in the usual model of cosmology, and even the usual model of physics.”
Exotic physics or a flawed model?
So, where did this S8 tension originate?
“We do not know, which is what makes this so exciting,” Ian McCarthy, a theoretical astrophysicist at Liverpool John Moores University within the U.K. and the co-author of three latest studies, told Space.com.
Computer simulations, nevertheless, like those carried out by FLAMINGO may very well be bringing us a step closer. They could help reveal the explanation for S8 tension because a grand, virtual map of the cosmos might assist with identifying possible errors in our current measurements. For instance, astronomers are slowly ruling out more mundane explanations for the problem, resembling the very fact it may very well be because of general uncertainties in observations of large-scale structures or related to an issue with the CMB itself.
In point of fact, the team speculates, perhaps the consequences of normal matter are quite a bit stronger than in current simulations. That too seems unlikely though, as simulations agree thoroughly with observed properties of galaxies and galaxy clusters.
“All of those possibilities are extremely exciting and have essential implications for fundamental physics and cosmology,” said McCarthy. Essentially the most exciting possibility, nevertheless, “is the Standard Model is inaccurate ultimately.”
For instance, dark matter could have exotic self-interacting properties not considered in the usual model — the S8 tension could also be signaling a breakdown of our theory of gravity on the most important scales, McCarthy said.
Nonetheless, while the newest simulations track effects of normal matter and subatomic particles often called neutrinos — each of that are found to be essential to make accurate predictions of how galaxies evolve across eons — they didn’t resolve the S8 tension.
Here’s the final word head-scratcher: At low-redshifts, the universe is significantly less lumpy than predicted by the usual model. But measurements that probe structures of the universe the CMB and low-redshift measurements are “fully consistent with standard model predictions,” McCarthy said. “It seems the universe behaved as expected for a major fraction of cosmic history, but that something modified in a while in cosmic history.”
Perhaps the important thing to resolving the S8 tension lies in the reply to what, exactly, drove that change.
This research is described in three papers published within the journal Monthly Notices of the Royal Astronomical Society.