Video menakjubkan ini menampilkan simulasi terbesar dan terinci dari alam semesta awal hingga saat ini

Dinamakan setelah dewi fajar, simulasi Thesan pada miliaran tahun pertama membantu menjelaskan bagaimana radiasi membentuk alam semesta awal.

Semuanya dimulai sekitar 13,8 miliar tahun yang lalu dengan “ledakan” kosmik besar yang tiba-tiba dan secara menakjubkan menciptakan alam semesta. Segera, alam semesta bayi mendingin secara dramatis dan menjadi benar-benar gelap.

Kemudian, dalam beberapa ratus juta tahun setelahnya[{” 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.

Simulasi evolusi dan radiasi gas ini menunjukkan perwujudan gas hidrogen netral. Warna mewakili intensitas dan kecerahan, mengungkapkan struktur reionisasi yang tidak lengkap dalam jaringan filamen gas netral berdensitas tinggi.

jembatan kosmik

Dengan komponen simulasi di tempat, tim menentukan kondisi awalnya selama sekitar 400.000 tahun setelah Big Bang, berdasarkan pengukuran yang tepat dari sisa cahaya Big Bang. Mereka kemudian mengembangkan kondisi ini ke depan dalam waktu untuk mensimulasikan petak alam semesta, menggunakan mesin SuperMUC-NG – salah satu superkomputer terbesar di dunia – yang secara bersamaan memanfaatkan 60.000 inti komputer untuk melakukan perhitungan Thesan pada setara dengan 30 juta CPU. . satu jam (upaya yang akan memakan waktu 3.500 tahun untuk dijalankan pada satu desktop).

Simulasi menghasilkan tampilan reionisasi kosmik yang paling detail, melintasi volume ruang terbesar, dari semua simulasi yang ada. Sementara beberapa simulasi berjalan pada jarak yang jauh, mereka melakukannya pada resolusi yang relatif rendah, sementara simulasi lain yang lebih rinci tidak menjangkau ukuran besar.

“Kami melintasi antara dua pendekatan ini: kami memiliki volume tinggi dan presisi tinggi,” Vogelsberger menekankan.

Analisis awal simulasi menunjukkan bahwa pada akhir reionisasi kosmik, jarak yang dapat ditempuh cahaya meningkat secara signifikan lebih dari yang diperkirakan para ilmuwan sebelumnya.

“Thesan menemukan bahwa cahaya tidak menempuh jarak yang jauh di alam semesta awal,” kata Canan. “Faktanya, jarak ini sangat kecil, dan hanya menjadi besar pada akhir reionisasi, meningkat 10 kali lipat hanya dalam beberapa ratus juta tahun.”

Para peneliti juga melihat petunjuk tentang jenis galaksi yang bertanggung jawab atas reionisasi. Massa galaksi tampaknya mempengaruhi reionisasi, meskipun tim mengatakan lebih banyak pengamatan, yang diambil oleh James Webb dan observatorium lainnya, akan membantu mengidentifikasi galaksi dominan ini.

“Ada banyak bagian yang bergerak di [modeling cosmic reionization]’, Vogelsberger menyimpulkan. “Ketika kita dapat menggabungkan semua ini dalam beberapa jenis mesin dan mulai menjalankannya dan menghasilkan alam semesta yang dinamis, itu bagi kita semua adalah momen yang sangat berharga.”

Referensi: “Proyek Berikutnya: Emisi dan Transfer Lyman-A selama Era Reionisasi” oleh A Smith, R. Cannan, E. Garaldi, M. Vogelsberger, R. Buckmore, dalam Sprinkle dan L. Hernquist, 24 Maret 2022, Tersedia di sini. Pemberitahuan Bulanan Royal Astronomical Society.
DOI: 10.1093/mnras/stac713

Penelitian ini didukung sebagian oleh NASA, National Science Foundation, dan Gauss Center for Supercomputing.