The Milky Way is not like other spiral galaxies. Instead of a nice, neat flat disc, it has a curve.
As we know and recently confirmed by two separate studies, the Milky Way is seriously curved around the edges, a strange feature that has puzzled astronomers for years.
Now a new analysis of the data from the Gaia mission has found an explanation: it is the result of a collision with a smaller galaxy in the past of the Milky Way.
It is unclear when or with which galaxy. It seems that the curvature could only have been caused by a relatively recent or even ongoing collision with one of the Milky Way's moons.
The Gaia mission has already done a great job revealing the past of our galaxy.
A collision with another galaxy 8-11 billion years ago inflated the disk of the Milky Way, filling it with stars. An encounter with a ghost galaxy millions of years ago left ripples in the hydrogen of the Milky Way. And let's not forget the collision with a galaxy called 'Sausage', which caused the stars to swing in special orbits.
The Gaia satellite was launched in 2013 and has since been collecting data to create the most accurate 3D map of the Milky Way. He carefully studies the correct motions, radial velocities and distances of stars to determine where everything is and how it is moving.
'It's like having a car and trying to measure the speed and direction of that car for a very short period of time, and then, based on those values, try to model the past and future trajectory of the car,' said astronomer Ronald Drimmel at the Turin Astrophysical Observatory. in Italy.
“If we take measurements like this for many cars, we could simulate traffic flow. Likewise, by measuring the apparent movements of millions of stars across the sky, we can simulate large-scale processes such as the movement of a galaxy. '
After carefully analyzing the data for 12 million stars, the team of astronomers found that the curvature of the Milky Way disk is not just in one place. It moves around the galactic center like stars, but at a different speed.
Although this speed is slower than that of stars, it is much faster than other previous explanations for the deformation, such as the dark matter halo effect or the intergalactic magnetic field, have allowed.
'We measured the strain rate by comparing the data with our models. Based on the speed obtained, the deformation will make one revolution around the center of the Milky Way in 600-700 million years, 'said astronomer Eloise Poggio from Turin. Astrophysical Observatory. (By comparison, the sun revolves around the galactic center every 220 million years.)
“This is much faster than we expected based on predictions from other models, such as those looking at nonspherical halo effects.”
This means that something stronger had to push the curvature; for example, let's say … collision with another galaxy.
So which galaxy? Well, that remains to be seen. Researchers believe it could be the Sagittarius Spheroidal Galaxy. It is in a fairly close orbit with the Milky Way.
Astronomers believe it has repeatedly passed through the plane of the Milky Way to form its rings, and there is evidence that it also associated with stars in the center of the galactic disk.
In the end, the Milky Way will emerge victorious by engulfing the Sagittarius Spheroidal Galaxy and turning on its globular clusters – but that day is still a long way off.
An analysis of the future and the next release of Gaia data, scheduled for some time later this year, could help figure out if this galaxy is the culprit for the warp, so we'll have to wait.
The study was published in the journal Nature Astronomy.
Sources: Photo: Stefan Payne-Wardenaar; Robert Gendler / ESO
