Discovery of an ancient galaxy 13.3 billion years ago, the most distant ever observed

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After the Big Bang, the first galaxies gradually appeared. Due to the expansion of the universe, these galaxies are moving away from us. An international team of astronomers has discovered signs of rotation in a galaxy that appeared 500 million years after the Big Bang, the most distant galaxy ever observed – using the Atacama Large Millimeter / Submillimeter Array (ALMA). This finding suggests that the galaxy has just begun to rotate, which will help scientists better understand the process of galaxy formation and evolution in the early universe.

The expansion of the universe after the Big Bang caused the galaxies to move away from each other, inducing a redshift in their emissions (shifting to longer wavelengths). By studying these shifts, it is possible to characterize the “motion” within the galaxies, as well as their distance.

With the technological advances of telescopes making them more and more powerful, astronomers have been able to discover more distant galaxies. The highlight is definitely the operational launch of the largest and most powerful space telescope in the world, the James Webb. It was also able to provide the deepest picture of the universe ever obtained, revealing galaxies over 13 billion years old – the Big Bang took place about 13.8 billion years ago. .

In a new study, astronomers from Waseda University have now revealed a probable rotating motion of a distant galaxy, dating to 13.3 million years ago, or 500 million years after the Big Bang, thanks to the telescopic terrestrial Atacama Large Millimeter / Submillimeter Array (ALMA) ). Their work is published in the journal The Astrophysical Journal Letters.

An image on the millimeter

Located on the Chajnantor plateau in the Chilean Andes, ALMA is an advanced telescope dedicated to studying radiation from the coldest objects in the universe. It consists of 66 high-precision antennas separated by several kilometers (up to 16 km). The observed radiation is called “millimeter / submillimeter” because it has a wavelength of the order of millimeters or less, between infrared radiation and radio waves.

At these wavelengths, the radiation emanates from giant interstellar cold clouds with temperatures a few tens of degrees above absolute zero, but also from the very first galaxies. Astronomers measure this radiation to study the chemical and physical conditions in molecular clouds, dense areas of gas and dust where stars are born. These areas are dark and opaque in visible light, but transparent in the millimeter and submillimeter portion of the electromagnetic spectrum.

ALMA is therefore particularly well-suited for observing redshifts in galaxy emissions. Recently, a team of international scientists observed the redshifted emissions from a distant galaxy, MACS1149-JD1. The team included Prof. Akio Inoue and graduate student Tsuyoshi Tokuoka from Waseda University (Japan), Dr. Takuya Hashimoto from the University of Tsukuba (Japan), Prof. Richard S. Ellis of University College London and Dr. Nicolas Laporte, researcher at the University of Cambridge (UK).

Ellis said in a statement: In addition to the search for high redshift, ie. very distant galaxies, the study of their inner motion of gas and stars gives motivation to understand the process of galaxy formation in the galaxy. oldest possible universe “.

By performing a series of observations over a period of two months, between October 2018 and December 2018, for a total of almost 10 hours of observation, astronomers successfully measured small differences in the “redshift” of one position to another, inside the galaxy itself. In other words, the galaxy rotates, it rotates.

Distribution of radio emission in MACS1149-JD1 observed by ALMA (left), compared to the model (right). The red color indicates that the galaxy is moving away from us, the blue color as it approaches, thus marking a rotation. © Tokuako et al., 2022 (modified by Laurie Henry for Trust My Science)

They then modeled the galaxy as a rotating disk that replicated the observations. The calculated rotational speed was about 50 kilometers per second (that of the Milky Way disk is 220 kilometers per second). The team also measured the diameter of the MACS1149-JD1 at just 3,000 light-years away. It is therefore much smaller than the Milky Way, which is 100,000 light-years in diameter. This galaxy would therefore only be at the beginning of its rotation.

Infographics summarizing the research performed on the MACS1149-JD1 galaxy. © Tokuako et al., 2022

Tracing the history of the universe

According to the authors, the origin of the rotation of galaxies lies in their process of formation. It is therefore necessary to find the first galaxies to reconstruct the history of the universe.

You should know that the formation of galaxies begins with the accumulation of gas and continues with the formation of stars from this gas. Over time, star formation progresses from the center outward, a galactic disk grows, and the galaxy acquires a specific configuration. As star formation continues, new stars form in the rotating disk, while older ones remain in the central part. By studying the age and motion of stars and gas in the galaxy, it is possible to determine the stage of evolution that the latter reached.

The artist’s impression of the MACS1149-JD1 galaxy. © Waseda University

Thanks to their modeling, the authors were able to determine the type of stars that make up the galaxy. In fact, the estimated mass based on the rotational speed of the galaxy corresponds to the star mass that results from the spectral signature of the galaxy. According to the authors, it comes mainly from many mature stars, about 300 million years old, and which was therefore formed more than 13.5 billion years ago. Dr. Takuya Hashimoto, co-author of the study, points out: This shows that the star population of JD1 was formed at an even earlier time in the cosmic age. “.

The authors conclude: rotational speed [de cette galaxie] is much weaker than those measured in galaxies of later epochs and our galaxy, and it is probably in an early stage of the evolution of rotational motion “.

With the James Webb Space Telescope, which has given us a glimpse of its extraordinary capabilities, astronomers are planning to verify and possibly update models of galaxy formation.

Source: The Astrophysical Journal Letters

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