Even if we can't see the first stars, we can trace their effects on the first galaxies.

Population III stars were the first stars in the universe. They were extremely massive, luminous stars, and many of them exploded as supernovae. How did they form the first galaxies? Credit: DALL-E

For a long time, our understanding of the universe’s first galaxies was largely theoretical. The light from that time reached us only after traveling for billions of years, and along the way it was dimmed and diffused into the infrared. Clues to the first galaxies are hidden in this dirty light. Now that we have the James Webb Space Telescope and its powerful infrared capabilities, we have seen the past and with greater clarity than ever before.

JWST has photographed some of the first. , leading to a flood of new insights and challenging questions. But it cannot see individual stars.

How can astronomers detect their effects on the universe’s first galaxies?

Stars are powerful, moving objects that exert a powerful force. They can fuse atoms into entirely new elements, a process called nucleosynthesis. Supernovae are particularly effective at this, as their powerful explosions release a storm of energy and matter that is released back into the universe.

Supernovae have existed since the early days of the universe. gave There are so-called Population III stars in the universe, and they were extremely massive stars. Massive stars are those that explode as supernovae, so population III stars will have a large number of supernovae.

The new research examines how all these supernovae may have affected their host galaxies. The paper “How Population III Supernovae Determined the Properties of the First Galaxies” has been accepted for publication. The Astrophysical Journal And there is Posted To arXiv. The lead author is K-Jung Chen from the Institute of Astronomy and Astrophysics, Academia Sinica, Taiwan.

Stellar metallurgy is the focus of this work. When the universe began, it consisted of primordial hydrogen, helium, and only trace amounts of lithium and beryllium. If you check your periodic table, these are the first four elements. Elements heavier than hydrogen and helium are called “metals” in astronomy, and metallicity in the universe increases over time due to stellar nucleosynthesis.

But hydrogen dominated the universe then as it does now. Only once the first stars formed and then exploded did other elements begin to play a role.

“The birth of early (Pop III) stars at z~20~25 marked the end of the cosmic dark ages and the beginning of the first galaxies. (SMBH) formation”, write the authors of the new paper. But their role as creators of astrometals is at the heart of the research.

The researchers used computer hydrodynamical simulations to examine how Pop III stars formed early galaxies. They saw (CCSNe), pair instability supernovae (PISNe), and hypernovae (HNe.).

Stars can only form from cold . When the gas is too hot, it is not dense enough to collapse into the protostellar core. The researchers found that when Pop III stars exploded as supernovae, they produced metals and dispersed them into the surrounding gas. Metals cooled the star-forming gas faster, allowing more stars to form faster. “Our results suggest that SNRs from the top-heavy Pop III IMF (initial mass function) produce more metals, leading to more efficient gas cooling in the first galaxies and earlier Pop II star formation.”

The simulations showed that supernova remnants (SNR) from Pop III SN fall toward the center of the dark matter halos in which they reside. “These Pop III SNRs and the primordial gas halo are pulled toward their core by gravity,” the authors explain. These SNRs sometimes collide and create turbulent flows. Turbulence mixes gas and metals from the SN and “forms filamentary structures that quickly form into dense clumps due to gas self-gravity and metal cooling.”

Even if we can't see the first stars, we can trace their effects on the first galaxies.

This research figure shows plots of metallicity (top) and temperature (bottom) from simulations of a 200 solar mass star forming, living a very short life, and then exploding as a supernova. is shown. The explosion creates impressions in the next stars. The left panels are right before star formation, the middle panels are 1.5 Myr after formation, and the right panels show 0.5 Myr after star death. After it exploded, it created a supernova remnant of hot and metal-rich ejecta. Metals in the ejecta would have contributed to the cooling of the gas, encouraging the rapid formation of the next generation of Pop II stars. Credit: Chen et al. 2024

This leads to more stars forming, although at this point, they are still Pop III stars. These have not been enriched by earlier Pop III supernovae and are still made of primordial gas. Some of these later Pop III stars reach the center of the halo before the early stars. This creates a complicated situation.

The authors write that the second generation of Pop III stars then “enforces strong radiative and SN feedback before the initial Pop III SNRs reach the halo center.”

Pop III stars heat the surrounding gas with their powerful UV radiation, as shown in the image above, preventing star formation. But they are. And they don’t live long. Once they explode, they spew metals into their surroundings, which can cool the gas and trigger more star formation. “After its short lifetime of about 2.0 Myr, the star dies as a PI SN, and its shock heats the gas to high temperatures (> 105 K) and ejects a mass of metals that cool. expands and promotes the transition to Pop II SF,” the authors explain.

Even if we can't see the first stars, we can trace their effects on the first galaxies.

This is Figure 6 from the research. It shows how Pop II stars are less massive than Pop III stars and how scattered clouds form in clusters. “Due to metal cooling and turbulence, these Pop II stars form in clusters with dense filaments around the halo center,” the authors write. Image credit: Chen et al. 2024

This is where Pop III stars formed the first galaxies. By injecting metals into star-forming gas clouds, they cooled the gas. Cooling ripped apart the star-forming gas clouds, causing the next generation of Pop II stars to become less massive. “Due to effective metallic cooling, the mass scale of these Pop II stars shifted to the low-mass end and formed into a cluster, as shown in the right panel of Figure 6.”

Pop III stars were mostly contained in dark matter halos. However, research shows how they formed the subsequent Pop II stars, which populated the early galaxies. One question astronomers have faced regarding the first galaxies is whether they were too crowded. -poor (EMP) pop II stars. But this research shows otherwise. “Thus we find that EMP stars were not typical of most ancient galaxies,” the authors conclude.

More information:
Ke-Jung Chen et al., How Population III Supernovae Determined the Properties of the First Galaxies, arXiv (2022). DOI: 10.48550/arxiv.2211.06016

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Reference: Even if we can’t see the first stars, we can trace their effects on the first galaxies (2024, February 16) https://phys.org/news/2024-02 on February 17, 2024 Retrieved from -stars-impact- galaxies.html

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