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Does the Milky Way move like a spinning top?

The Milky Way It is a spiral galaxy, which means that it consists among other components of a disk of stars, gas and dust where the spiral arms are immersed. Initially it was assumed that the disk was totally flat, but it has already been known for some decades that the outermost part of this region has distortions, it is what is known as’warp‘: in one direction it is twisted upwards, and in the opposite – downwards.

The warped stars, gas, and dust are, therefore, in a plane other than that of the large central part of the disk, and the axis perpendicular to the new planes defines their axis of rotation.

In 2020, an investigation announced the detection of the precession (movement like that of a spinning top) of the warping of the Milky Way disk, that is, the deformation that this outermost region of our galaxy presents is not static, but rather, like a spinning top itself, the orientation of its axis of rotation also changes over time.

A new study questions a relevant finding on the dynamics of the Milky Way in recent years: the variation of the axis of rotation of the warp or distortion up and down of the disk of the Milky Way

In addition, the researchers found that this is faster than theories predict: one cycle every 600-700 million years, about three times the time it takes for the Sun to rotate around the center of the Milky Way.

Precession is not unique to the Milky Way, but it also happens to our planet. In addition to the annual translational movement of the Earth around the Sun and the rotational movement of just under 24 hours, the Earth’s axis precesses and does so with a periodicity of about 26,000 years, which means that the pole star does not it has always been close to the north celestial pole, since 14,000 years ago it was close to the star Vega.

Now a work done by Žofia Chrobáková Y Martin Lopez Corredoira of the Institute of Astrophysics of the Canary Islands and the University of La Laguna has taken into account the variation in the amplitude of the warp with the age of the stars. The study, published in The Astrophysical Journal, concludes that using the warping of old stars, whose speeds are measured, could result in the precession disappearing or being slower than is currently believed.

Gaia mission data

To arrive at this result, the researchers have made use of data from the Gaia mission of the European Space Agency (ESA), analyzing the positions and velocities of hundreds of millions of stars in the outer disk.

“It had not been taken into account in previous work that the warp for stars with a few tens of millions of years old, such as Cepheids, is much greater than the warp for stars visible with the Gaia mission, which are thousands of millions of years, ”explains Chrobáková.

“This does not mean that warping does not precess at all, it could do so, but much more slowly, and we will probably not be able to accurately measure this movement until we have better data,” concludes López Corredoira.

Reference:

Žofia Chrobáková and Martín López Corredoira. “A case against a significant detection of precession in the Galactic warp.” The Astrophysical Journal, 2021

Rights: Creative Commons.

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