Is overeating to blame for the bulges in the Milky Way bar? –ScienceDaily

A new simulation run on the world’s most powerful supercomputer dedicated to astronomy has produced a testable scenario to explain the appearance of the bar of the Milky Way. Comparing this scenario with data from current and future space telescopes will help clarify the evolution of our home galaxy.

Astronomy is revealing the structure of the Milky Way galaxy we live in in ever-increasing detail. We know it to be a disk galaxy, with two- or four-armed spirals, with a straight bar in the middle connecting the spirals. Now we also know that the inner part of the bar has a “peanut-shaped bulge”, places where the bar is thicker, protruding above and below the midplane of the Milky Way and a “nuclear bulge “, which is discy and located in the central part of the Milky Way. Some other galaxies, but not all, show similar bulges of two types.

Like dieters who suddenly discover bulges, astronomers have asked the question, “How did bulges of two types form?” To answer this question, a team led by Junichi Baba at the National Astronomical Observatory of Japan (NAOJ) simulated a possible scenario for a Milky Way-like galaxy on “ATERUI II” at NAOJ, the world’s most powerful supercomputer. world dedicated to astronomy. The team’s simulation is the most comprehensive and accurate to date, including not only the stars in the galaxy, but the gas as well. It also incorporates the birth of new stars from gas and the death of stars as supernovae.

The formation of a bar helps channel the gas to the central part of the galaxy, where it triggers the formation of new stars. So it might be reasonable to assume that the nuclear bugle in the galaxy is created from new stars born there. But the simulations show that there are almost no new stars in the bar outside of the nuclear bulge, because the bar is so good at funneling gas to the center. This means gas scraping is not the reason a peanut-shaped bulge develops in the bar. Instead, the team finds that gravitational interactions can pull some of the stars into orbits that take them above and below the midplane.

The most exciting part is that the simulation provides a testable scenario. Because the peanut-shaped bulge acquires no new stars, all of its stars must predate the formation of the bar. At the same time, the bar channels gas to the central region where it creates many new stars. Thus, almost all of the stars in the nuclear bulge will be born after the bar has formed. This means that stars in the peanut-shaped bulge will be older than stars in the nuclear bulge, with a clear break between ages. This break corresponds to the moment when the bar was formed.

Data from the European Space Agency’s Gaia probe and the future Japanese JASMINE satellite will help determine the movements and age of stars and test this scenario. If astronomers can detect a difference between the ages of stars in the peanut-shaped and nuclear bulges, it will not only prove that overeating is not to blame for the peanut-shaped bulge, it will tell us the age of the bar in the Milky Way Galaxy.


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Material provided by National Institutes of Natural Sciences. Note: Content may be edited for style and length.

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