2023-09-27 09:52:23
Space
The Milky Way is undergoing a slimming treatment
According to a study published Wednesday, the Milky Way weighs 200 billion times the mass of the Sun, five times less than previously estimated.
Updated September 27, 2023, 11:52
The Milky Way is a disk some 100,000 light years across.
AFP
The Milky Way would have a mass four to five times lower than that calculated so far, according to a study published Wednesday, the conclusions of which shake up knowledge of the characteristics of our galaxy. This result is the “fruit of the Gaia revolution”, explains to AFP astronomer François Hammer, co-author of the study published in “Astronomy and Astrophysics“. Gaia, a satellite dedicated to mapping the Milky Way, delivered the positions and movements of 1.8 billion stars, in its latest catalog, in 2022.
That is a tiny fraction of the total contained in our spiral galaxy, a disk of some 100,000 light years in diameter, made up of four large arms – one of which houses our solar system – which stretch around an extraordinarily luminous.
“Reassessment of mass”
The study of the Gaia catalog made it possible to calculate the rotation curve of the Milky Way with unprecedented precision, according to the authors of the study. The exercise consists of establishing the speed at which celestial bodies rotate around the center of the galaxy.
Observations of spiral galaxies had until now concluded that this curve was “flat”, that is to say that once a certain distance from the center was reached, the rotation speed was constant. However, here, “this is the first time that we discover that beyond its disk, the curve falls”, explains François Hammer, “as if there was not much material” between 50 and 80,000 years from the galactic center.
With the consequence of a “reassessment of the mass of our Milky Way to values considered extremely low”, of the order of 200 billion times the mass of the Sun, five times less than previously estimated.
“Daring conclusions”
The study by the international team, carried out by astronomers from the Paris Observatory and the CNRS, has a second major consequence. It “calls into question the relationship between luminous matter and dark matter,” continues the astronomer.
This hypothetical dark matter is also called dark matter because it is so far invisible and undetectable. It is supposed to provide the mass necessary for the cohesion of galaxies, and represent approximately six times the mass of luminous matter, made up of stars and gas clouds. For the Milky Way, the study’s calculations see this ratio significantly lower, with only three times more dark matter than luminous matter.
Conclusions deemed “daring”
Conclusions that astronomer Françoise Combes, although a colleague of François Hammer at the Paris Observatory, judges to AFP to be “a little too daring”, or even “perhaps not entirely well-founded”. Notably because the study focuses on a reduced radius of the galaxy, while astronomers, in general, calculate the mass of the galaxy taking into account much larger distances.
However, in addition to gases, globular clusters, dwarf galaxies or even the Magellanic Cloud, “we have a lot of dark matter up to these distances”, and as much corresponding mass, notes Françoise Combes, a leading specialist in evolution. galaxies. However, she welcomes “very precise work, which improves our knowledge of the stars and their rotation”, up to around 80,000 light years from the galactic center.
Singular character
François Hammer’s team defends this work by arguing for the unique character of our galaxy. Unlike many spiral galaxies, which experienced violent collisions between galaxies six billion years ago, the Milky Way has “evolved much more quietly and calmly over the past nine billion years,” according to François Hammer.
Another possibility to justify the difference between the Milky Way and other spiral galaxies: the method of observation. Which relies on the stars for the first, and on the gas clouds for the second. In the meantime, for Françoise Combes, the Milky Way “is not exceptional at all”, and as for dark matter, “it is like the others”.
(AFP)Show comments
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