Why is the galaxy curved? Scientists received an unexpected answer: because it is affected by another star system, which will soon collide with ours.
Details are set out in a scientific article published in the journal Nature Astronomy.
The disk of the Milky Way is curved: one of its edges is raised, and the other is lowered. The first indications of this fact appeared in the late 1950s, and recently it has finally been confirmed.
Where does this bend come from? Experts have offered various versions. According to one of them, the magnetic field of the Galaxy is to blame. Another hypothesis suggests that the cloud of dark matter into which the Milky Way is immersed has an asymmetric shape. Therefore, scientists say, the gravity of dark matter bends the disk of the Galaxy.
The new study relies on an unprecedentedly accurate measurement of the shape of the Milky Way. It was carried out thanks to the Gaia orbital telescope, according to which the richest star catalog in history has been compiled. The tool helped determine the coordinates and speeds of more than a billion stars. This is not so much compared to the total number of luminaries in the Galaxy (hundreds of billions), but much more than was previously studied.
Selecting 12 million giant stars located in the outer regions of the disk, the authors tracked the change in the shape of the latter.
Thanks to new data, astronomers have found that bending is not static. He moves through the galaxy. The previously curved parts of the disk are straightened, while the adjacent ones are bent.
“Based on the speed obtained, the bend will complete one revolution around the center of the Milky Way in 600-700 million years,” says Eloisa Poggio from the Turin Astrophysical Observatory.
Milky Way Form. Illustration by Stefan Payne-Wardenaar; NASA / JPL-Caltech; ESA
For comparison: the Sun makes a complete revolution around the center of the Galaxy in 220 million years, that is, about three times faster. But astronomers did not expect such speeds from the bend of the Galaxy.
This is much faster than the shape of the Milky Way could change due to the magnetic field or the attraction of dark matter. Therefore, the authors have another hypothesis.
They believe that the matter is the gravity of a small galaxy, which is located near ours and in the near future by astronomical standards, is likely to crash into it. Which of the star systems surrounding the Milky Way is engaged in such cosmic hooliganism is not yet clear. Perhaps we are talking about one of its closest satellites – a dwarf elliptical galaxy in Sagittarius.
The location of the dwarf galaxy in Sagittarius relative to the Milky Way. Illustration ESA / Gaia / DPAC, CC BY-SA 3.0 IGO.
The authors emphasize that the movement of the bend does not affect life on Earth.
“The sun is 26 thousand light-years away from the center of the galaxy, where the strain amplitude is very small,” Poggio explains. “Our measurements mainly related to the outer parts of the galactic disk, 52 thousand light-years from the center of the galaxy and beyond.”
