The discovery of a primordial galaxy from 13.3 billion years ago, the farthest 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 noticed signs of rotation in a galaxy appearing 500 million years after the Big Bang, the farthest galaxy ever observed – using the Atacama Large Millimeter/submillimeter Array (ALMA) . This finding suggests that the galaxy is just beginning to rotate, which will help scientists better understand the process of galaxy formation and evolution in the first Universe.

The expansion of the Universe after the Big Bang caused the galaxies to move away from each other, causing redshift in their emissions (shifting towards a higher wavelength). By studying these movements, it is possible to identify “motion” within galaxies, as well as their distance.

With the advancement of the technology of telescopes, making them more powerful, astronomers have been able to detect more distant galaxies. The highlight is sure to be the start of operation of the world’s largest and most powerful space telescope, James Webb. It also provides the deepest image of the Universe ever captured, revealing galaxies that are more than 13 billion years old – the Big Bang occurred about 13.8 billion years ago. .

In a new study, astronomers from Waseda University have now revealed a possible spinning motion in a distant galaxy, dated 13.3 million years ago, or 500 million years after the Big Bang, thanks to the Atacama Large Millimeter/submillimeter Array (ALMA) terrestrial telescope. ). Their work was published in the journal The Letters of the Astrophysical Journal.

A millimeter image

Located on the Chajnantor high plateau of the Chilean Andes, ALMA is a state-of-the-art 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 in the order of millimeters or less, between infrared radiation and radio waves.

At these wavelengths, radiation comes from giant interstellar cold clouds with temperatures a few ten degrees above absolute zero, but also from early galaxies. Astronomers measure this radiation to study the chemical and physical state of the molecular cloud, dense regions of gas and dust where stars are born. These regions are dark and opaque in visible light, but transparent in the millimeter and submillimeter parts of the electromagnetic spectrum.

ALMA is therefore particularly suited to observing redshifts in galaxy emissions. Recently, a team of international researchers observed red-shifted emissions from a distant galaxy, MACS1149-JD1. The team includes 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 from University College of London and Dr Nicolas Laporte, researcher at the University of Cambridge (United Kingdom).

Ellis said in a statement: Beyond the search for long redshift, i.e. very distant, galaxies, the study of their internal movement of gas and stars provides impetus to understand the process of galaxy formation. oldest possible universe “.

By conducting a series of observations over two months, between October 2018 and December 2018, over a total of nearly 10 hours of observation, astronomers successfully measured the small difference in the “redshift” of a position to another, right within the galaxy. . In other words, the galaxy is spinning, it is spinning.

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

They then modeled the galaxy as a spinning disk, mimicking the observations. The calculated rotational speed is about 50 kilometers per second (which on the Milky Way disc is 220 kilometers per second). The team also measured the diameter of the MACS1149-JD1 at just 3,000 light-years away. So it is smaller than the Milky Way, which is 100,000 light years in diameter. So this galaxy is only at the beginning of its rotation.

Infographic summarizing the research done on the MACS1149-JD1 galaxy. © Tokuako et al., 2022

Tracing the history of the Universe

According to the authors, the beginning of the rotation of galaxies is in their process of formation. So it is necessary to find the first galaxies to rebuild the history of the Universe.

You should know that the formation of galaxies starts to accumulate gas and continues to form stars from this gas. Over time, star formation progresses from the center to the outside, a galactic disk grows, and the galaxy acquires a particular configuration. As star formation continues, new stars form on the spinning disk while the older ones remain in the central part. By studying the age and movement of the stars and gases in the galaxy, it is possible to determine the stage of evolution that reached later.

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 mass estimated from the galaxy’s rotational speed is equivalent to the stellar mass resulting from the galaxy’s spectral signature. According to the authors, it predates from many adult stars, is about 300 million years old, and therefore formed more than 13.5 billion years ago. Dr. Takuya Hashimoto, co -author of the study, pointed out: This indicates that the stellar population of JD1 was formed at an earlier time in the cosmic age. “.

The authors conclude: rotational speed [de cette galaxie] weaker than those measured in later galaxies and in our galaxy, and it is likely to be in the early stages of developing rotational motion. “.

With the James Webb Space Telescope, which gives us a glimpse of its unique capabilities, astronomers plan to confirm and possibly update models of galaxy formation.

Source: The Astrophysical Journal Letters

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