Astronomers explained the strange bend of our galaxy

UNITED STATES (OBSERVATORY NEWS) — After analyzing the data from the Gaia space telescope, astronomers concluded that the curvature of the edges of our galaxy was caused by a relatively recent collision with one of the smaller neighboring galaxies.

The results of the study are published in the journal Nature Astronom.

The Milky Way is not like other spiral galaxies. Instead of a beautiful, neat flat disk, it has a “spine” curve. Astronomers have long been trying to find an explanation for this.

It seems that the riddle was solved thanks to the Gaia space telescope of the European Space Agency (ESA), which has been collecting data for the seventh year to compile an accurate 3D map of the Milky Way. It carefully fixes the position of all moving objects of our galaxy, their radial velocities and the change in the distances between the stars.

Gaia’s mission has already revealed in the past the Milky Way a series of events that determine the current features of the galaxy. So, 8-11 billion years ago, a collision with another galaxy led to the fact that the thick disk of the Milky Way in certain places was swollen, filled with new stars.

Around the same time, the Milky Way merged with the dwarf galaxy Gaia Enceladus, also known as the sausage galaxy, resulting in at least eight globular clusters with 50 billion solar masses of stars, gas and dark added to the Milky Way matter. Another ghostly dwarf galaxy has left the so-called “hydrogen ripples” in the outer disk of the Milky Way.

After analyzing data for 12 million stars, astronomers found that the curvature of the Milky Way disk is not in one place, but moves around the galactic center, like stars, but at a different speed. Although this speed is slower than that of stars, it is too fast for the previously proposed explanations for the curvature of the edges of the galaxy – such as the halo effect of dark matter or the intergalactic magnetic field.

The simulation results based on the new Gaia mission data showed that this is most likely the result of a collision with a smaller galaxy. It is not yet clear when this happened and what kind of galaxy it was, but judging by the parameters of the rotation of the bend, it was a very recent collision – perhaps even it has not yet been fully completed – from one of the Milky Way’s satellite galaxies.

“We measured the rate of disk deformation by comparing the data with our models,” the press release says the first author of the study, Eloisa Poggio from the Turin Astrophysical Observatory.

“Based on the obtained speed, the deformation will make one revolution around the center of the Milky Way for 600 “700 million years. This is much faster than we expected based on the predictions of other models, such as those based on the non-spherical halo effect.”

For comparison, the Sun makes a complete revolution around the galactic center in 220 million years.

As a candidate for the role of a collision partner, scientists consider the dwarf elliptical galaxy in Sagittarius SagDEG – the satellite of the Milky Way, located in a fairly close orbit, which often ends with devastating events. The SagDEG Galaxy passed through the plane of our galaxy several times. The last time this happened was between 200 and 100 million years ago.

Scientists believe that with each such passage the dwarf galaxy in Sagittarius loses its stars, and the Milky Way will eventually swallow it. It is expected that once the Milky Way will collide with its other satellites – the galaxies of the Big and Small Magellanic Clouds. But this will not happen soon, in about 2.4 billion years.


This article is written and prepared by our foreign editors writing for OBSERVATORY NEWS from different countries around the world – material edited and published by OBSERVATORY staff in our newsroom.

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