Discovery of a primordial galaxy that begins its rotation


Researchers have just discovered the galaxy the furthest rotation ever observed. It crossed over 13.26 billion light years before reaching us and is called MACS1149-JD1, abbreviated to JD1. But what makes it special is hers rotation speed : JD1 rotates much slower than the spinning galaxies of earlier times. ” The rotation speed of JD1 is much slower than those found in later galaxies and in our own Galaxy and it is likely that JD1 is in an early stage of development of rotational motion “, explains Akio Inoue, co-author of a study published in the journal The astrophysical diary and professor at Waseda University.

The formation of the first galaxies, still mysterious today

There is still no consensus on the formation of the very first galaxies. The most accepted theory suggests that they were formed as a result of the primordial fluctuations of the densities, which are at the origin of the structure of the Universe. These fluctuations have given rise to dense zones, composed of both black matter and of gas. Gradually this gas condensed and this mass of matter grew: the very first galaxies were born during the reionizationcomposed only ofhydrogen and’heliumthe lighter elements of the periodic table. Star formation only comes into play after these are created primordial galaxies. It is when a cloud of gas contained in the galaxy, called nebulacollapses on itself from gravitation only one star the shapes. 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 is, then gradually this star formation is displaced.

The setting in rotation develops from the first instants of the galaxies, when they are still only haloes of matter. But then it accelerates, propelled by the formation of stars that accentuate the gravitational effects experienced on both sides of the galaxy. Therefore, to determine the stage ofevolution of a galaxyThey astronomers use the properties of the stars and the gases that compose them, such as their movement or their age. For these observations, they use the effect of gravitational lens : when a particularly massive object distorts the light of the objects behind it relative to the observer. This effect allows you to “grow” some objects that are too faint to be observed directly, amplifying the light they emit. However, they appear distorted, forcing researchers to reconstruct them from the collected data.

JD1 allows to date the late rotation of primordial galaxies

But the galaxy that interests us today is just JD1. Discovered by the Alma telescope (Array Atacama Large Millimeter / Submillimeter), located in Chile, well designated for this, was thanks to various observation campaigns carried out between October 2018 and December 2018, for a total of almost 10 hours of observation. To find out his age, the researchers measured his age thanks to Alma red shiftalso called ” red shift “. Corresponds to the offset of the spectrum bright towards greater wavelengths when an object moves away from the observer. This is the doppler effectthe same that changes the perception of the notes of the ambulance siren: the sound seems higher when it approaches (small wavelength), and lower when it moves away.

However, due to the expansion of the Universe, the older a galaxy is, and therefore the farther it is, the faster it moves away from us. With a particularly high spectral shift (z = 9.1), the researchers assigned it a stellar population of a few hundred million years, thus suggesting an older formation epoch, around az = 15. “In addition to the discovery of highly redshift galaxies, that is, very distant galaxies, the study of their internal movement of gas and stars provides motivation to understand the process of formation of galaxies in the most distant Universe. Possible old”explains Professor Richard S. Ellis, co-author of the study and a researcher at theUniversity college from London.

With a diameter of 3,000 light years, compared to the 100,000 of the Milky Way, it turns out, as the study explains, dominated by rotation, and not by dispersion: the dispersion of velocities is much lower than the rotation speed of the stars that make up the galaxy. This property allowed the team to model JD1’s dynamics and deduce other characteristics. In particular the stars that compose it. It contains many mature stars, about 300 million years old, thus formed more than 13.5 billion years ago. “This shows that JD1’s stellar population formed at an even earlier time in the cosmic era,” explains Dr Takuya Hashimoto, study co-author and researcher at Tsukuba University.

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