2024-04-11 17:00:00
A particularly comprehensive simulation study has expanded the range of parameters that can explain how the universe is built – but has still not managed to crack a disturbing cosmological puzzle
Ever since physics was freed from the shackles of philosophy, around the time of Newton, it has been dominated by the view that sees the experiment as the final arbiter. However, nowadays there is another dominant player in the research field – simulation. Its role is so important that there is almost no existence for modern research in physics without the simulations: sterile virtual environments designed to replace, precede or confirm the findings of experiments and observations.
Simulations are especially powerful in the study of astrophysics and cosmology. It is partly due to the enormous size of the universe, because of which there are things that cannot be measured easily, and things that cannot be measured at all. The James B. Space Telescopelaunched at the end of 2021, greatly advanced the capabilities of observational astrophysics, but in many areas the difficulty remains, and simulations are still an essential tool. A new system of cosmological simulations called Flamingo (FLAMINGO – the initials of a long name whose meaning is not important for our purposes), now wants to shed light on the question of “S8 stretching” – one of the most challenging and hot puzzles in space exploration.
Simulations are especially powerful in the study of astrophysics and cosmology. A simulation of the formation of the universe Patrick Landmann / Science Photo Library
What do we know that we don’t know?
The leading models in the study of cosmology explain how the universe was created And what will probably be the end. Between the beginning and the end, cosmological dynamics drives the universe. The standard model of cosmology, called Lambda-CDM (acronym for “cold dark matter to matter”), includes a limited set of parameters that fit a rich variety of cosmological and gravitational data. It is possible to build a model of a universe that is mostly complex from dark matter and from dark energy, to fit these parameters.
To understand what dark matter and dark energy are, one must know that the measured accelerations of bodies in the galaxy do not conform to Newton’s laws, which are the governing laws in the classical mechanics of bodies such as stars, planets, gas clouds and more. Experiments show that the matter moves too fast relative to the amount of mass – and if so, why doesn’t it detach from the galaxy? In addition, the speed of the material at the edges of the galaxy does not decrease as you move away from its center, as should happen assuming that all the mass is concentrated inside the galaxy.
From statistical calculations and calculations based on the accelerations of the celestial bodies and Newton’s second law, it appears that the mass of our galaxy, the Milky Way, is approx.580 billion solar massesand there are those who believe that even more. The mass of all the visible matter in the galaxy is about 46 to 64.3 billion solar masses, so the mass of the gas we know of its existence by observation is at most 10-15 percent of the mass of the entire galaxy. A simple calculation shows that there is a lot of missing mass. And in other words, we don’t know how to explain 85 percent of the gravity in the universe. The prevailing, but not the only, explanation for this gap is that there is dark matter in the universe, which cannot be detected by conventional means simply because it does not maintain any interaction with the electromagnetic force.
Another unexplained phenomenon is that there seems to be a force pushing the galaxies away from each other, against the effect of gravity pulling them towards each other. The galaxies in the universe are moving away from each other at an increasing speed, although gravity is supposed to decrease the speed at which they are moving away. The name given to this mysterious force, whose origin we do not know, is “dark energy”. These two concepts are a puzzle and not a solution, because they balance the equations with the observations, but we know nothing about their nature.
The standard model of cosmology includes a limited set of parameters that fit a rich variety of cosmological and gravitational data. Illustration of the model, from the Big Bang to the present NASA/ LAMBDA Archive / WMAP Science Team
Prof. Rani Bodnik From the Department of Particle Physics and Astrophysics at the Weizmann Institute of Science, he is a cosmologist who studies the north of dark matter with the help of experiments. In a conversation with the Davidson Institute website, he says: “Our understanding of the universe, as it is reflected from the Big Bang and measurements of the cosmic background radiation – which is, in a sense, a greeting from the past, from the beginning of the universe – provides answers to most of the essential questions, and takes into account almost exclusively the dark matter, Because he is the one who determines the dynamics on the cosmological scale.”
As you probably understand, here comes a big “but”. “In the last 10-12 years, cosmologists have started asking questions about what happens near the centers of galaxies,” Bodnik adds. “Galaxies and stars and the entire world known to us are made of what is called ‘baryonic matter’, and near the centers of galaxies the cosmology begins to change and strange phenomena occur. For them the usual simulations will no longer provide the goods.”
Thus, the new simulations, the result of the work of researchers from universities in Great Britain and the Netherlands, take into account not only parts of the universe while ignoring the rest, as their predecessors did, but a much larger amount of parameters and components that may be involved in cosmological dynamics.
This time dark matter and dark energy were taken into account, as well as baryonic matter, which many previous simulations ignored simply because its contribution to gravity is low compared to dark matter. Neutrino particles were also taken into account, which are the lightest elementary particles known to particle physicists today, and which also do not interact with the electromagnetic force.
We do not know how to explain 85 percent of the gravity in the universe. The prevailing explanation for this gap is that dark matter exists in the universe. Simulation of the distribution of dark matter in the universe Volker Springel / Max Planck Institute For Astrophysics / Science Photo Library
The bully you don’t want to mess with
“Exact calculations that do not ignore the baryonic matter are bordering on the impossible,” Bodnik says. “The interactions they have are incredibly complicated, so these calculations usually introduce the baryonic matter as a disturbance and in a phenomenological form, that is, one where the emphasis is on matching observations and less on theoretical accuracy.”
The baryonic matter interacts with the electromagnetic force, which is manifested in the radiation and pressure it exerts, as well as in galactic winds – which we do not know how to predict and it is difficult to plant them in models. These galactic winds are fast gusts and streams of gas that are ejected during the formation of new stars, or those that result from supermassive black holes and other powerful cosmological events.
This time the spirits were introduced into the simulations using machine learning algorithms, which has also stormed into astrophysics and cosmology in recent years, and their dynamics are described using tools from the field of fluid mechanics.
To all of these is added a certain tension, a discrepancy known as “S8 tensions”. This tension is manifested primarily in unexpected changes in the density distribution of galaxies; A kind of unknown secret related to the behavior of gravity, which science knows – or at least thinks it knows.
S8 is a measure of changes in the density of matter in the universe: how uneven the distribution of matter is. And in technical terms – how inhomogeneous the universe is. The value of this measure can be calculated using the Standard Model of Cosmology and measurements of the cosmic background radiation; And independently, it can also be calculated through measurements of weak gravitational distortion – a phenomenon in which the gravitational field of objects with a very high mass bends light rays from the environment, much like an optical lens does. But there is a problem – these two calculations do not agree with each other. This mismatch is stretching S8.
“S8 tension has been with the research world for about a decade,” says Bodnick. “Apparently, in regions far from the center of the galaxy there should be no nonlinearity of the cosmological dynamics, since the dark matter is distributed approximately uniformly, and the baryonic matter should not dramatically affect the dynamics and the mass. Nevertheless, the statistics based on observations around the baryonic matter show an anomaly not expected”.
S8 is a measure of changes in the density of matter in the universe: how uneven the distribution of matter is. Illustration of the structure of matter in the universe Equinox Graphics / Science Photo Library
Data, data, data
The new study is divided for three articles: The first article describes the methods, the second presents the simulations and the third the findings, with an emphasis on S8 stretching. All three were published in the journal Monthly Notices of the Royal Astronomical Society in August last year.
The reasons for the existence of S8 pranks are shrouded in fog. Some claim that new physics, which deviates from the standard model, may explain the gap – but as of today we do not know what it is. In their work, the researchers compare and verify the simulations with experimental observations, for example Gravity drainage or Soniayev-Zeldowitz effect(Sunyaev-Zel’dovich), which is a distortion of the cosmic background radiation resulting from the scattering of photons (light particles) by hot electrons in galaxy clusters.
Adding the baryonic matter requires much more computing power than usual. However, the researchers say they succeeded in their ambitious mission and examined the beginning of the universe through the glasses of the new imaging – the data from which amounts to several petabytes (trillion bytes). This is a huge amount of information, by any measure.
One of the simulations in the Flamingo series takes into account 300 billion particles, each of which has the mass of a small galaxy. All these galaxies, a bit like at the end of the movie “Men in Black”, exist inside a virtual cube whose length is ten billion light years. A light year is about nine trillion kilometers, so it is a huge size. All the simulations were written in a new code developed especially for them, which performs calculations in thirty thousand computer cores.
“It’s important to take things in proportion,” Bodnik concludes. “This work is not very unique in its field, although it provides a novelty for us. With some degree of regret, we can update that the researchers have not yet been able to understand the reasons for the existence of S8 stretching, but this is another stop on the way there. In our quest to understand it, the universe does not run away Place”.
#flamingo #sheds #light #beginning #universe