Stars rich in precious metals were born more than 10 billion years ago, elucidated by simulation of the Milky Way Galaxy | sorae Portal site to the universe

[▲ Distribution of stars (yellow) and gas (blue) in the Milky Way galaxy formation simulation (Credit: Yutaka Hirai)]

A research team headed by Yu Hirai, a researcher at the Graduate School of Science, Tohoku University, has discovered that many stars rich in precious metals (elements heavier than iron, such as gold and platinum) found in the Milky Way galaxy will later form the Milky Way galaxy. Research results have been announced that it was born more than 10 billion years ago in a small galaxy.

In the early universe, only hydrogen, helium, and a small amount of lithium existed. Heavier elements up to iron were generated and released by nuclear fusion reactions inside stars, and heavier elements were generated and released by violent phenomena such as supernova explosions. It is thought that it gradually increased as the alternation of generations of stars progressed.

Many stars in the Milky Way have a ratio of precious metals to iron that is more than five times that of the Sun. To understand when and how these precious metal-rich stars were formed, the research team used the National Astronomical Observatory of Japan’s astronomical supercomputer “Aterui II” to simulate the formation of the Milky Way galaxy over 13.8 billion years. carried out. As a result, it is said that more than 90% of the stars rich in precious metals may have formed in small galaxies in the process of forming within 4 billion years after the birth of the universe (more than 9.8 billion years ago).

[▲ Video of the test simulation in this research (calculated at 1/100 resolution of the actual test)]
The yellow glow represents stars, and the pale cloud-like objects represent gas.
(Credit: Takayuki Saito/Takaaki Takeda)

This simulation takes into account the process of nucleosynthesis called the “r-process,” in which precious metals are produced in conjunction with the explosive phenomenon “kilonova” that occurs when neutron stars merge. In small galaxies, the amount of hydrogen gas, which is the raw material for stars, is small, and even with a small number of neutron star mergers, the proportion of precious metals in the entire galaxy is high. .

In addition, when comparing the amount of europium (Eu), one of the precious metals, both the simulation and the actual observation data showed a similar distribution. From this, the research team points out that many of the precious metal-rich stars found in the Milky Way have been formed for more than 10 billion years, and that they are stars that tell the history of the Milky Way’s formation in the early universe. increase.

[▲ Comparing the distribution of days of europium (Eu) and iron (Fe) between the Milky Way galaxy formation simulation (blue) and the actual observation (orange) (Credit: Yutaka Hirai et al.)]

The research team will use RIKEN’s supercomputer “Fugaku” to perform simulations and observations from the National Astronomical Observatory of Japan’s Hawaii Observatory’s “Subaru Telescope.” It is said that we will challenge the elucidation of

connection:Kilonova GW170817 detects lanthanum and cerium, first detection of lanthanides in neutron star merger

Source

• Tohoku University – Stars rich in precious metals are 10 billion years old Successful simulation of the world’s highest resolution Milky Way galaxy
• National Astronomical Observatory of Japan – Stars rich in precious metals are 10 billion years old -Successful simulation of the Milky Way galaxy with the world’s highest resolution-
• Yutaka Hirai et al. – Origin of highly r-process-enhanced stars in a cosmological zoom-in simulation of a Milky Way-like galaxy

Text / Takehiro Matsumura