Discovery of a primordial galaxy beginning its rotation

Researchers have just discovered that galaxy furthest rotation ever observed. It crossed 13.26 billion light-years before reaching us and is called MACS1149-JD1, shortened to JD1. But what makes it special is it rotation speed : JD1 rotates much more slowly than rotating galaxies from less ancient times. ” That rotation speed of JD1 is much slower than those found in galaxies of later epochs and our galaxy, and it is likely that JD1 is in an early evolutionary stage of rotational motion. explains Akio Inoue, co-author of a study published in the journal The Astrophysical Journal and Professor at Waseda University.

The formation of the first galaxies, still a mystery today

There is still no consensus on the formation of the very first galaxies. The most accepted theory is that they arose after the original density fluctuations that form the origin of the structure of the universe. These fluctuations resulted in dense zones composed of both black matter and from gas. Gradually this gas condensed and this mass of matter grew: the very first galaxies were born during the reionizationconsisting only ofhydrogen and D’heliumthe lightest elements of the periodic table. Star formation only comes into play after their formation primeval galaxies. It is when a Cloud of gas contained in the galaxy fogcollapses in on itself gravity only star To form. In a galaxy, this process comes into play many times, first at the level of the galaxy’s center where most of the dust and gas resides, then gradually this star formation is leveled out.

The rotational dislocation develops from the first moments of the galaxies, when they are only matter halos. But then it accelerates, fueled by star formation that accentuates gravitational effects on either side of the galaxy. So to determine the stageevolution of a galaxyshe astronomers Use the properties of the stars and the gases that make them up, such as B. their movement or their age. For these observations they use the effect of gravitational lens : when a particularly massive object distorts the light of objects behind it in relation to the viewer. This effect makes it possible to “grow up” certain objects that are too faint to be observed directly by amplifying the light they emit. However, they appear distorted, forcing researchers to reconstruct them from the data collected.

JD1 makes it possible to date the late rotation of primordial galaxies

But the galaxy that interests us today is actually JD1. Discovered by the Alma telescope (Atacama Large Millimeter/submillimeter Array), which is located in Chile and is well suited for this, it was for a total of almost 10 hours of observation thanks to various observation campaigns carried out between October 2018 and December 2018. To find out his age, thanks to Alma, the researchers measured his age redshiftalso called ” redshift “. It corresponds to the offset of the spectrum bright to bigger wavelengths when an object moves away from the viewer. That is the Doppler effectthe same that changes the perception of the sounds of the ambulance siren: the sound appears higher as it approaches (small wavelength) and lower as it recedes.

Due to the expansion of the universe, however, a galaxy moves away from us faster the older and thus further away it is. With a particularly high spectral shift (z = 9.1), the researchers assigned it a stellar population a few hundred million years old, which indicates an older formation epoch around z = 15. “Beyond the discovery of high redshift, i.e. very distant, galaxies, the study of their inner motion of gas and stars provides a motivation to understand the process of galaxy formation in the most distant universe.”explains Professor Richard S. Ellis, co-author of the study and researcher atuniversity from London.

With a diameter of 3,000 light-years compared to 100,000 for the Milky Way, the study explains, it turns out rotation dominates, and not by scattering: the scattering of velocities is much smaller than the rotation speed of the stars that make up the galaxy. This property allowed the team to model the dynamics of JD1 and infer other properties from it. Especially the stars who compose it. It contains many mature stars that are around 300 million years old, i.e. formed more than 13.5 billion years ago. “This shows that the stellar population of JD1 formed at an even earlier point in the cosmic age,” explains Dr. Takuya Hashimoto, study co-author and researcher at Tsukuba University.

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