2023-05-21 12:09:35
A beautiful rotating spiral with four main arms emerging from a bulge of stars in the center. That is the image that we all have of the Milky Way, the galaxy in which we live. However, that representation of our home in space is pure theory. Nobody, in fact, has been able to see the Milky Way from the outside to really know what it is like… The situation is equivalent to trying to guess what a building is like by looking out one of its windows. We will see a fragment of the façade, but never the entire building.
For this reason, scientists have been making partial measurements for decades, putting together pieces of an impossible puzzle and comparing the galactic fragments that we can observe from Earth with other galaxies in the sky. It is ironic to say the least that we know exactly the exact shape of thousands and thousands of galaxies ‘out there’, but we are not sure what ours looks like…
And now, to top it off, a team of space scientists from the Chinese Academy of Sciences have just published a study in ‘The Astrophysical Journal’ to tell us that the traditional image we have of the Milky Way is wrong. Measurements of it, in effect, suggest that our galaxy may have a very different shape than we thought.
three main ways
In general, and collecting data from thousands of observations throughout the Universe, galaxies seem to prefer three main shapes: elliptical, irregular, and spiral. And, within the third group, to which we belong, most of the galaxies display large ‘arms’ that arise from the center and branch out into smaller arms.
That would be precisely the case of our Milky Way, with its large spiral arms emerging from a thick central bulge of stars. But according to the researchers, having four arms makes our galaxy an extremely rare ‘bug’, an outlier and very difficult to observe in other galaxies. If the Milky Way really had that strange shape, it should also have some unique properties that allow it to have four arms instead of two, which is the norm for the vast majority of known spiral galaxies.
So does our galaxy have two arms instead of four? After analyzing multiple sources of astronomical data, the authors of the new study believe so. “Despite much work,” the authors write, “the general morphology of the spiral structure of the Milky Way remains somewhat uncertain. But in the last two decades, precise distance measurements have given us the opportunity to solve this problem.”
Making a new star map
The researchers relied on data from a whole new generation of instruments, capable of much more precisely measuring the distances between Earth and individual stars. Thus, after obtaining the distances of some 200 different stars, the scientists were able to begin to develop the outline of a new map of the Milky Way. To this initial ‘skeleton’ they later added the latest data from the European Gaia space telescope, which precisely determines the movements of millions of individual stars with respect to Earth.
Thus, the article says, “and using for the first time the precise locations of very young objects, we propose that our galaxy has a multi-armed morphology consisting of two-armed symmetry.” Thus, they explain, the arms of Norma and Perseus are probably the two symmetrical arms in the inner Milky Way. As they extend from the interior of the galaxy to the outer parts, they bifurcate and connect with the Centauri and Sagittarius arms, respectively.”
loose arms
On the other hand, the authors argue that on the outskirts of the Milky Way there are other “distant and fragmented irregular arms” that are not connected to the central bulge of the galaxy, where most of its stars reside. The fragmentation of these ‘loose’ spiral arms could be due to ancient collisions of the Milky Way with other galaxies or even with galaxy clusters throughout its long history.
The researchers claim that this new model of the Milky Way may provide an alternative basis for future studies on its shape and structure. Studies to be carried out in the coming years with the publication of new Gaia data and measurements of the distances of more stars carried out with multiple telescopes. In this way, little by little, and despite being inside, we will be able to get an increasingly accurate idea of what the galaxy in which we have had to live is really like.
#Milky #doesnt #shape #thought