Simulation predicts what James-Webb will be able to see in the first billion years of the universe

In the 1960s, two phenomena were discovered. astrophysics who quickly established the theory big Bang Georges Gamow and Georges Lemaitremaking increasingly untenable the previous standard cosmological model, in which the observable cosmos was only a part Universe endless. An ever-expanding universe without beginning or end, in which the processes of creation to matter spawned new galaxies maintain a constant density of the material despite the diluting effect of the expansion.

These phenomena were quasarswhich are now known to be the most likely supermassive black holes Kerr accretes a lot of matter during rotation, and cosmic radiation.

Quasars have strong linesepisode Lyman alpha, i.e. release photons in the region ofultraviolet well described Bohr model belonging’atom hydrogen, which deexcites in a certain way. These emission lines are also produced in the same way by the substance heated at birth. stars in galaxies.

in redshift from range quasars, which are measured by a value denoted by “z”, which is the higher, the farther the quasar is observed, that is, at the beginning of the history of the observed cosmos, indicates to us in accordance with the law Hubble Lemaitre that they mostly contain billionslight years belonging Milky Way. We also observe a number of linesabsorption in the spectrum of a quasar. This is the same Lyman-alpha emission line absorbed by matter between the quasar and the instrument on Earth. But because the distances to quasars vary, we also see lines shifting with distance, which eventually form what are called Lyman-alpha forests.

Paradoxically, as evidenced by taking into account at the moment the effect found astrophysicists James Gunn and Bruce Peterson in 1965. Indeed, neutral hydrogen, which is known to exist between galaxies, should block the measurable Lyman-alpha radiation fairly quickly by absorbing it. Unless you imagine that some of the hydrogen present is ionized.

For 13.8 billion years, the universe has continued to evolve. Contrary to what our eyes tell us, when we contemplate the sky, what makes it up is far from static. Physicists observe the different ages of the universe and run simulations in which they reproduce its formation and evolution. It would seem that dark matter played a big role from the moment of the origin of the Universe to the formation of large structures observed today. © CEA Research

Cosmic reionization

However, the discovery and interpretation of the existence of fossil radiation in the framework of the Big Bang theory and its study based on measurements made Planck’s satellitein particular, tell us that approximately 380,000 years after the Big Bang, the emission of fossil radiation is due to the formation of hydrogen atoms andhelium neutral, the temperature of the plasma formed fromions and D’electrons leading them to their downfall due to the expansion of the cosmos to unite.

Thus, cosmologists have come to the conclusion that a few hundred million years after the emission of cosmic radiation, something happened that led to reionization ordinary matter of the observed space.

It is believed that this is simply the formation of the first stars in the first galaxies, and alsoaccretion matter the first giant black holes that would produce radiation that would not only lead to what is called the end dark times (at the beginning of which there were no stars yet), but also, at the same time, during reionization (The era of reionization or EoR in English), more than 13 billion years ago.

Cosmologists would like to understand in detail the timing of reionization, because it carries information about the birth of stars and galaxies. So far, we have only had a timid and limited access start to the end of reionization with telescopes like Hubble but everything has to change one day James Webb telescope will be fully operational in a few months.

There is another radiation that can give us information not only about what happened during the dark ages, but also during reionization. That clouds neutral hydrogen can actually emit radiation radio across in the famous 21 cm parting. You need to be able to observe, map and study a kind of equivalent of background radiation. blurred fossil, but produced this time by the neutral hydrogen clouds of these two periods. Much in this regard is expected from the commissioning radio telescopes Array of square kilometers (SKA).

An excerpt from Thesan’s simulation with a core in the past, which starts with observations at a spectral shift measured with z, which is high and decreases over time. We can see both the reionization that progresses in the composition of neutral hydrogen and the collapse of this hydrogen in galaxies and filaments of galaxy clusters, caused by the collapse of dark matter and which is also taken into account in the simulation. © Thesan simulators

Simulation to reproduce the history of the early universe

However, in all cases, a model is needed to interpret the observations, observations that, in turn, serve to test the hypotheses underlying the model. However, it turns out that if we can understand up to a certain point what happened in the course of several tens of millions of years after the Big Bang, by simple analytical calculations with linear approximations equations used, it is no longer possible after that, because it is necessary to deal with the non-linear mode of these equations, and then numerical simulation is necessary.

For decades, these simulations have been run to understand the birth of galaxies and how they coalesce into large filamentous structures over time. Initially, the goal was to describe the effect gravity about distribution black matter just because he is the essence weight in the form of matter. But over time, we realized – like the growth of strength computers eventually allowed this to be done – which also had to take into account the subtle effects of the behavior of baryonic matter. Thus, a burst of star formation in a young galaxy leads to an outburst supernovae whose explosive explosion can push the baryonic gas out of the galaxy, changing the distribution of ordinary matter and, therefore, being a response under the influence of the force of gravity the distribution of dark matter, as well as how clouds of matter will accumulate in galaxies and cause them to grow.

One of the latest such simulations is called Thesan and was developed by scientists at the Massachusetts Institute of Technology, Harvard University and the Max Planck Institute for Astrophysics. She was named after the Etruscan goddessdawn, Thesan, as it is specifically designed to simulate cosmic reionization. What can be seen by reading an article on the subject, published in Royal Astronomical Society Monthly Noticesa publicly available version can be found at arXiv, it breaks records of sophistication in this regard by accurately modeling the production of radiation by stars, supernova explosions, and the radiation of supermassive black holes, as well as the impact of this radiation on galaxies and the intergalactic medium, which is also driven by its material inputs. , for example in the form filaments of cold dark matterevolution of galaxies.

Thesan Simulation was implemented on SuperMUC-NG, one of the largest supercomputers in the world, which simultaneously used 60,000 computing cores to perform Tesan calculations on the equivalent of 30 million CPU. Building on a previous simulation called Illustris-TNG, which it expands on, it breaks the record not only for extensive consideration of various astrophysical phenomena that have occurred since the release of fossil radiation, but also for volume fromspace-timewhere we accurately describe the epoch of reionization (i.e. between approximately 380,000 years and a billion years after the Big Bang), namely the cubic volume of the observable universe extending over 300 million light years and in which we follow the emergence and evolution of hundreds of thousands of galaxies.

Another excerpt from the Thesan simulation, showing on the left the decrease in volume of neutral hydrogen clouds over time and consistent with observations as z decreases. On the right, the formation of the number of stars in galaxies increases, the number of ionizing photons in the intergalactic medium also increases with time and decreasing z. © Thesan simulators

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