On dark nights, far from the lights of the city, you can see that many stars are scattered like a white line, almost like someone spilling milk across the sky. Especially in the southern hemisphere, where the phenomenon due to the slope of the Earth's axis becomes extremely obvious.
What we see is our own galaxy, the Milky Way, or the Milky Way, as it is called in English, and some of its 200-400 billion stars, which come together in a spiral pattern, like in a more or less flat disk. The spiral's diameter is about 120,000 light-years, and our own solar system – with Earth and all planets – is about 27,000 light-years from the center of the galaxy.
So far, however, the image of our own galaxy has been based largely on indirect measurements or extrapolations from how other galaxies look. Our idea for the appearance of the Milky Way was based on a number of assumptions rather than specific observations, which made it difficult to understand exactly what it looked like.
But now two research groups have completed independently the most comprehensive three-dimensional mapping of our galaxy done so far. And the result is surprising. Instead of being a flat plate, though of slightly different thickness, the mapping shows that the Milky Way is curved in an S-shape.
The first map, made by Chinese and Australian scientists, was presented at Nature Astronomy in February, while the second, now featured in Science magazine, was made by Polish scientists.
Our map shows that the Milky Way is uneven. Instead, it is curved and bent. This is the first time we use separate objects to show this in three dimensions, says one of the researchers behind the study, Przemek Mróz of Warsaw University in a video on Science.
Finding from Earth how the galaxy we live in is not so easy. The best way, of course, would be to measure the distance to different stars or constellations in relation to our own sun and then relate the measurement values between these individual objects to a more or less complete "map". The problem, however, is the interstellar dust and gas clouds that exist in the seemingly empty space and, like fog in the sea, obscure the view.
On the lake you use headlights whose bright lights penetrate the fog. The universe also has one type of headlamp: a cepheid. Cepheid is a relatively young giant or even super giant star that shines hundreds or thousands of times stronger than our own sun. But above all, the cepheids have a somewhat strange feature that their brightness varies or pulses with a certain regularity. The point is that with these periodic variations, researchers can calculate the true brightness of the cepheid, its absolute magnitude, and thus the exact distance to it.
And it is with the help of such cepheids, 2,431 of them, that Polish scientists have now created the most detailed map of the Milky Way so far. The result shows that our spiral galaxy is bent in S-shape.
"We don't know why, but we think this turn is caused by interactions with satellite galaxies, small dwarf galaxies that are quite common in the Milky Way (near the galaxy)," wrote the first author of the article, Dorothy Scowron, in an email to TT. "Other possible explanations are interactions with intergalactic gas or dark matter."
Using the pulsing light of cepheids, scientists can not only calculate the distance to them. The light also says something about their age. In this way, Polish scientists were also able to make a kind of age map of the Milky Way, which clearly shows that the oldest stars are located on the outer edges of the galaxy, in the farthest from the spiral arms, while the younger ones closer to the middle. On the outer edges, it is not uncommon to encounter a cepheid, which is nearly 400 million years old, while in the middle they "only" have about 30 million years of neck.
The study currently confirms this, presented in February, although Australian and Chinese researchers used less cepheids, 1339 instead of 2431. However, it is striking that this study also shows that the Milky Way has an S-shaped curve. This study also showed that the appearance of the Milky Way is not stable. Instead, our galaxy is becoming more distorted.