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The Milky Way is really deformed

For centuries, astronomers have been studying the Milky Way to better understand its size and structure. And while modern instruments have produced invaluable observations of our galaxy and others (which have allowed astronomers to get a general picture of their appearance), a truly accurate model of our galaxy has been elusive.

For example, a recent study conducted by a team of astronomers from The National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) have shown that the disk of the Milky Way is not flat (as previously thought). According to their findings, it seems that the Milky Way is deforming and twisting more and more as one moves away from the nucleus.

The study detailing its findings recently appeared in the scientific journal. Nature, entitled "An intuitive 3D map of the precession of the galactic warp traced by classic Cepheids". The study was led by Xiaodian Chen, of the Key Laboratory for Optical Astronomy at NAOC, and included members of the Kavli Institute of Astronomy and Astrophysics at Peking University and Western China. Normal university

Using information from Gaia's second data release, a team of scientists has made refined estimates of the mass of the Milky Way. Credit: ESA / Gaia / DPAC

To decompose it, galaxies such as the Milky Way are made up of thin discs of stars that orbit around a central bulge once every few hundred million years. In this bundle, the gravitational pull of hundreds of billions of stars and dark matter hold together the gas and matter of the galaxy. However, in the furthest regions of the galaxy, the hydrogen atoms that make up most of the gas disk are no longer confined to a thin plane.

As Dr. Chen explained in a recent press release from the Kavli Institute:

"It is very difficult to determine the distances from the Sun to parts of the outer gas disk of the Milky Way without having a clear idea of ​​how that disk actually looks. However, we recently published a new catalog of periodic variable stars known as classic Cepheids, for which you can determine such precise distances from 3 to 5%.. "

Classic Cephied are a subclass of Cephied Variables, a type of star that stands out for the way it pulsates regularly, varying both in diameter and in temperature. This produces changes in brightness that are predictable in terms of period and amplitude and makes them very useful for measuring galactic and cosmic distances.

The galaxy of the Milky Way, disturbed by the interaction of the tides with a dwarf galaxy, as predicted by the simulations of N-bodies. Credit: T. Mueller / C. Laporte / NASA / JPL-Caletch

Classical Cepheids are a particular type of giant giants and bright yellow supergiants that are 4 to 20 times more massive than our Sun and up to 100,000 times brighter. This implies that they have short lifetimes that sometimes last only a few million years before exhausting their fuel. They also experience pulsations that can last for days or even a month, which makes them very reliable to measure distances to other galaxies.

As Dr. Shu Wang of the Kavli Institute of Astronomy and Astrophysics and co-author of the article said:

"Much of our Milky Way is hidden by dust, which makes it difficult to measure distances to the stars. Fortunately, observations at long infrared wavelengths can overcome this problem."

For the sake of their study, the team established a 3D Galactic Disc model based on the positions of 1,339 Classical Cephieds. From this, they were able to provide strong evidence that the galactic disk is not in line with the galactic center. In fact, when viewed from above, the disk of the Milky Way appears to be S-shaped, with one side curved upwards and the other curved downwards.

Three-dimensional distribution of classic Cepheid stars in the warped disk of the Milky Way (red and blue dots) centered on the location of the Sun (shown as a large orange symbol). Credit: Chen Xiaodian / Kavli Institute of Astronomy and Astrophysics

Said Professor Richard de Grijs of Macquarie University, one of the main co-authors of the article:

"To our surprise, we found that our Cepheid stars and the gas disk of the Milky Way are closely watched in 3D, which offers new insights into the formation of our galaxy of origin, perhaps more important in the outer regions of the Way. Milky, we found that the S-type stellar disc is deformed into a progressively twisted spiral pattern. "

These findings recall what astronomers have observed of a dozen other galaxies, which showed progressively twisted spiral patterns. By combining their results with those observations, the researchers concluded that the spiral pattern of the Milky Way is probably caused by the rotational forcing (also known as "torques") of the internal disk.

This latest study has provided an updated map of the stellar motions of our galaxy, which shed light on the origins of the Milky Way. In addition, it could also inform our understanding of the formation of galaxies and the evolution of the cosmos.

Additional readings: Kavli Institute of Astronomy and Astrophysics, Nature

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