Birth and death of stars seen near the beginning of time

Until recently, astronomers could not observe the first stars and galaxies that formed in the universe. This occurred during what is known as the “Cosmic Dark Ages”, a period which took place between 380,000 and 1 billion years after the Big Bang. Thanks to new generation tools like the James Webb Space Telescope (JWST), improved methods and software, and updates to existing observatories, astronomers are finally piercing the veil of this era and getting a glimpse into how the Universe as we know it got started.

This includes new observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, which obtained images of a stellar nursery within a galaxy about 13.2 billion light-years away in the constellation Eridanus. This galaxy has a redshift value greater than 8.3, corresponding to when the Universe was less than 1 billion years old. The images identified sites of star formation and possible star death within a nebula (MACS0416_Y1) located within this galaxy. This represents a milestone for astronomy as this is the furthest distance such structures have been observed in our Universe.

The team was led by Yoichi Tamura, an astronomy graduate student at Nagoya University. It was joined by researchers from the National Astronomical Observatory of Japan (NAOJ), the Waseda Research Institute for Science and Engineering, the Tomonaga Center for the History of the Universe (TCHoU), the Cosmic Dawn Center (DAWN), DTU-Space, the Max Planck Institute for Extraterrestrial Physics (MPE), the Research Center for the Early Universe, the Frontier Science and Social Co-creation Initiative (FSSI), the Research Center for Statistical Machine Learning, and several universities. The paper describing their findings recently appeared in The Astrophysics Journal.

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During these cosmic dark ages, the Universe was permeated by clouds of neutral hydrogen, and the only sources of light were the relict radiation left over from the Big Bang – visible today as the Cosmic Microwave Background (CMB) – and the radiation created by the reionization of hydrogen. This occurred as the first population of stars (Population III), which were very bright and hot by modern standards, pumping out huge amounts of ionizing energy. This led to the Epoch of Reionization, when the Universe became transparent and its structures became visible to modern telescopes.

In this case, the team previously detected radio waves emitted by oxygen and dust – two components of the interstellar medium (ISM) and star-forming nebulae – which absorbed radiation from the birth of new stars. However, their initial observations lacked the resolution to conduct detailed observations that would have revealed the distribution of dust and gas and the structure of the nebula. To this end, the team used ALMA to observe MACS0416_Y1 for 28 hours, which revealed that the dust signal and oxygen emission regions are tightly intertwined.

The images released by the team (shown above) show dust emissions alone from ALMA (right), while the image on the left shows specific emission data combined with starlight imaged by the Hubble Space Telescope. Dust is represented by red, oxygen by green, and starlight by blue. The vertically elongated cavity, which may be a superbubble, is visible in the center of the dust emission image on the right, appearing as an oblong-shaped black section.

Takuya Hashimoto, a University of Tsukuba astronomer and co-author of the paper, described the challenges of obtaining these observations in a recent NOAJ news release, saying, “It’s like capturing the extremely faint light emitted by two fireflies located 3 centimeters apart on the summit of Mount Fuji as seen from Tokyo, and being able to distinguish between these two fireflies.”

Their findings suggest a process in which newly formed stars within the nebula ionize the surrounding gas. In addition, the team found a huge cavity extending about 1,000 light-years in the dust-dominated regions. This cavity may be a “superbubble,” created when several short-lived stars collapse, leading to successive supernovae that scatter the nebulae with their shock waves. This is consistent with measurements of gas motion in nebulae, which indicate an environment where many stars may have formed together in massive clusters.

These results offer a preview of what future observations using next-generation telescopes may discover. As Tamura explained:

In the future, more detailed information may be obtained by conducting high-resolution observations of these same star clusters, using instruments such as the James Webb Space Telescope and the planned Extremely Large Telescopes.

Further reading: NAOJ, The Astrophysics Journal