Krátky klip zo simulácie Theson. Pozrite si video v článku nižšie.
Thesonova simulácia z prvej miliardy rokov, pomenovaná po bohyni úsvitu, pomáha vysvetliť, ako žiarenie formovalo raný vesmír.
Všetko sa to začalo asi pred 13,8 miliardami rokov veľkým kozmologickým „výbuchom“, ktorý priviedol vesmír k existencii náhle a veľkolepo. Krátko nato sa detský vesmír dramaticky ochladil a úplne stmavol.
Potom, po niekoľkých stovkách miliónov rokov[{“ attribute=““>Big Bang, the universe woke up, as gravity gathered matter into the first stars and galaxies. Light from these first stars turned the surrounding gas into a hot, ionized plasma — a crucial transformation known as cosmic reionization that propelled the universe into the complex structure that we see today.
Now, scientists can get a detailed view of how the universe may have unfolded during this pivotal period with a new simulation, known as Thesan, developed by scientists at MIT, Harvard University, and the Max Planck Institute for Astrophysics.
Named after the Etruscan goddess of the dawn, Thesan is designed to simulate the “cosmic dawn,” and specifically cosmic reionization, a period which has been challenging to reconstruct, as it involves immensely complicated, chaotic interactions, including those between gravity, gas, and radiation.
The Thesan simulation resolves these interactions with the highest detail and over the largest volume of any previous simulation. It does so by combining a realistic model of galaxy formation with a new algorithm that tracks how light interacts with gas, along with a model for cosmic dust.
Evolution of simulated properties in the main Thesan run. Time progresses from left to right. The dark matter (top panel) collapse in the cosmic web structure, composed of clumps (haloes) connected by filaments, and the gas (second panel from the top) follows, collapsing to create galaxies. These produce ionizing photons that drive cosmic reionization (third panel from the top), heating up the gas in the process (bottom panel). Credit: Courtesy of THESAN Simulations
With Thesan, the researchers can simulate a cubic volume of the universe spanning 300 million light years across. They run the simulation forward in time to track the first appearance and evolution of hundreds of thousands of galaxies within this space, beginning around 400,000 years after the Big Bang, and through the first billion years.
So far, the simulations align with what few observations astronomers have of the early universe. As more observations are made of this period, for instance with the newly launched James Webb Space Telescope, Thesan may help to place such observations in cosmic context.
For now, the simulations are starting to shed light on certain processes, such as how far light can travel in the early universe, and which galaxies were responsible for reionization.
“Thesan acts as a bridge to the early universe,” says Aaron Smith, a NASA Einstein Fellow in MIT’s Kavli Institute for Astrophysics and Space Research. “It is intended to serve as an ideal simulation counterpart for upcoming observational facilities, which are poised to fundamentally alter our understanding of the cosmos.”
Smith and Mark Vogelsberger, associate professor of physics at MIT, Rahul Kannan of the Harvard-Smithsonian Center for Astrophysics, and Enrico Garaldi at Max Planck have introduced the Thesan simulation through three papers, the third published on March 24, 2022, in the Monthly Notices of the Royal Astronomical Society.
Follow the light
In the earliest stages of cosmic reionization, the universe was a dark and homogenous space. For physicists, the cosmic evolution during these early “dark ages” is relatively simple to calculate.
“In principle you could work this out with pen and paper,” Smith says. “But at some point gravity starts to pull and collapse matter together, at first slowly, but then so quickly that calculations become too complicated, and we have to do a full simulation.”
To fully simulate cosmic reionization, the team sought to include as many major ingredients of the early universe as possible. They started off with a successful model of galaxy formation that their groups previously developed, called Illustris-TNG, which has been shown to accurately simulate the properties and populations of evolving galaxies. They then developed a new code to incorporate how the light from galaxies and stars interact with and reionize the surrounding gas — an extremely complex process that other simulations have not been able to accurately reproduce at large scale.
“Thesan follows how the light from these first galaxies interacts with the gas over the first billion years and transforms the universe from neutral to ionized,” Kannan says. “This way, we automatically follow the reionization process as it unfolds.”
Finally, the team included a preliminary model of cosmic dust — another feature that is unique to such simulations of the early universe. This early model aims to describe how tiny grains of material influence the formation of galaxies in the early, sparse universe.
Thesonova simulácia vývoja plynu a žiarenia ukazuje vykreslenie neutrálneho vodíkového plynu. Farby predstavujú hustotu a jas, odhaľujúc nejednotnú reionizačnú štruktúru v sieti vlákien neutrálneho plynu s vysokou hustotou.
kozmický most
Na základe presných meraní zvyškového svetla z Veľkého tresku spolu so zložkami simulácií určil tím ich počiatočné podmienky na približne 400 000 rokov po Veľkom tresku. Potom tieto podmienky ďalej vyvinuli, aby simulovali časť vesmíru pomocou stroja SuperMUC-NG – jedného z najväčších svetových superpočítačov – ktorý súčasne využíval ekvivalent 30 miliónov CPU na výpočet tesonov. Používa sa pre 60 000 výpočtových jadier. hodín (úsilie, ktoré by trvalo 3 500 rokov, aby fungovalo na pracovnej ploche).
Simulácia priniesla najpodrobnejší pohľad na znovuzjednotenie vesmíru v najväčšom priestore zo všetkých existujúcich simulácií. Zatiaľ čo niektoré simulácie modelujú na veľké vzdialenosti, robia to s relatívne nízkym rozlíšením, zatiaľ čo iné, podrobnejšie simulácie nie vo veľkých množstvách.
„Prepájame tieto dva prístupy: máme veľký objem aj vysoké rozlíšenie,“ zdôrazňuje Vogelsberger.
Skoré analýzy simulácií ukazujú, že na konci kozmického opätovného spojenia sa vzdialenosť, ktorú svetlo dokázalo prekonať, zvýšila dramatickejšie, ako si vedci predtým mysleli.
„Thesson zistil, že svetlo neprechádza vo vesmíre na veľké vzdialenosti,“ hovorí Kannan. „V skutočnosti je táto vzdialenosť veľmi malá a zväčšuje sa až na konci opätovného spojenia, pričom sa v priebehu niekoľkých stoviek miliónov rokov zväčší desaťkrát.“
Výskumníci tiež vidia známky toho, aké typy galaxií sú zodpovedné za opätovnú ionizáciu. Zdá sa, že hmotnosť galaxie ovplyvňuje reionizáciu, hoci tím tvrdí, že ďalšie pozorovania Jamesa Webba a iných observatórií pomôžu zúžiť tieto veľké galaxie.
„Je v tom veľa pohyblivých častí [modeling cosmic reionization]“ uzavrel Vogelsberger.
Referencia: „The Theson Project: Lyman – An Emission and Transmission of the Epoch of Reionization“ od A. Smitha, R. Kannana, E. Garaldiho, M. Vogelsbergera, R. Pakmorea, V. Springela a L. Hernquista, 24. marca 2022, Mesačné oznámenia Kráľovskej astronomickej spoločnosti,
DOI: 10.1093/mnras/stac713
Tento výskum podporila NASA, National Science Foundation a Gauss Center for Supercomputing.
