Ultimately, the Milky Way is not a flat and uniform disk

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The Milky Way is a spiral galaxy often depicted as a flat, even disk. Faithful representations of our galaxy are extremely difficult to obtain because of our position within it. However, new observations tend to show that, far from being a flat disk, the geometry of the Milky Way is drastically changing to its periphery.

Astrophysicists have discovered that the further one moves away from the galactic center, the more the Via Lattea's disk becomes curved, bent or even twisted. His galactic plane is not a straight line; instead, it looks a little more like an elongated S. The results of the observations have been published in the journal Natural astronomy.

" It is notoriously difficult to determine the distances between the Sun and some parts of the Milky Way's external disc without having a clear idea of ​​its appearance. Says Xiaodian Chen, an astronomer at the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC).

One solution is to use a type of star called the Cepheid variable. They are very bright stars that pulsate with a precise frequency, which allows astronomers to calculate their absolute magnitude. This therefore makes it possible to calculate the distances from these stars.

In the optical spectrum, dust and gas between us and the star can prevent the precise determination of brightness, which means that the resulting distance calculations are a little uncertain. But the infrared radiation can penetrate into the dust, which allows for a more precise result.

3d map Cepheids

Three-dimensional map of the Milky Way, obtained from Cepheids. Credits: Xiaodian Chen et al. 2018

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" We have used a new catalog of infrared observations obtained with the WISE space observatory, to reduce the effects of dust and determine the distances that separate us from our Cepheids with uncertainties of less than 3-5%: an accuracy at this point. unprecedented day Explains Richard de Grijs of Macquarie University in Australia.

" Combined with their apparent positions in the sky, we constructed a three-dimensional map of the Milky Way traced by these Cepheids, which we compared to the gas distribution. Both seemed to deviate from a flat disk ".

It is not unusual for a spiral galaxy to deform at the edges, particularly with atomic hydrogen gas extending beyond the star disk. What makes the Curvature of the Milky Way so interesting is that it includes the stars, especially the young stars.

" The precession of the disk seems to imply that the massive internal disk of the Milky Way could force the external disk to follow its rotation, but the rotation of the external disk is late, which causes the torsion Dice de Grijs.

" This had never been seen before in the Milky Way, but Frank Briggs had discovered it several years ago for a dozen large Near spiral Universe galaxies. Combining its results, we believe that the same dynamic is at stake in the Milky Way ".

This result provides a better understanding of the three-dimensional structure and dynamics of our galaxy and will establish a higher limit on the amount and distribution of matter in the galaxy – which will be " particularly interesting in the context of the question in which dark matter is found Grijs concludes.

Source: Natural astronomy

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