Our galaxy, the Milky Way, is far from a peaceful place. It spins, it wobbles and, as a new study just revealed, it also undulates. New data from ESA’s ç have discovered a colossal wave, dubbed “the great wave” that propagates through the galactic disk in a very similar way to the waves we have in a pond when we throw a stone.
The study. This phenomenon, which has been identified by the team led by Eloisa Poggio of the Istituto Nazionale di Astrofisica in Italy, is a “large-scale vertical corrugation” that superimposes the already known deformation that our galaxy constantly undergoes. In essence, we are facing a wave that causes entire bands of stars to move “up” and “down.”
Great proportions. It is nothing like the waves that we see on our beaches, logically, since we are talking about something on a galactic level. In this case, astronomers have known since the 1950s that the Milky Way’s disk is not flat, but rather warped (or “warped”) at its edges. Now this study adds an additional structure that no one knew was there.
Thanks to Gaia’s incredibly precise measurements, which map the 3D position and 3D motion of stars, the team was able to analyze two populations of young stars: giant stars and classical Cepheids. These maps revealed a gigantic wave that is now coming to light.
The figures. In order to understand the magnitude of this phenomenon, we can take into account the following parameters of this phenomenon:
- Height: the movement of the stars is about 150-200 parsecs, which is up to 650 light years above and below the galactic plane.
- Length: The structure spans at least 10,000 light years and possibly up to 20,000.
- Location: affects a vast section of the outer disk, in regions located tens of thousands of light years from the galactic center.
The test. The most fascinating thing about the discovery is not just the shape of the wave, but the evidence that it is moving. “What makes this even more compelling is our ability, thanks to Gaia, to also measure the movements of stars within the galactic disk,” explains Poggio.
To understand it, the team used a perfect analogue: the wave of a stadium. If we were to freeze the wave that is made in the stands of a stadium, we would see some people standing (the crest), others who have just sat down (the back part) and others who are about to get up (the front part). Something similar happens in the galaxy.
The astronomers discovered that the stars with the highest vertical position (the crest) were not the same as the stars with the highest vertical velocity. The maximum speed point was displaced, with a 90º approach phase difference.
This phase difference is irrefutable proof that it is a propagating wave. And not only that: the stars inside the corrugation also show a systematic radial motion of 10-15 km/s outward. The conclusion is clear: it is a wave that travels from the interior of the galaxy to its furthest reaches.
There is a mystery. Researchers have measured the wave, but don’t know what caused it. The main hypothesis is that the Milky Way suffered an encounter or collision with a smaller dwarf galaxy, but it is not 100% certain. Previous simulations have shown that interaction with a satellite galaxy, such as Sagittarius, can excite exactly these types of vertical waves and corrugations in the galactic disk.
This “great wave” is much larger and much further away than the famous Radcliffe Wave, a filament of gas about 9,000 light years long located near our Sun. Although both are ripples, scientists believe that they are two different characteristics, although they do not rule out that they may be related in some way.
Since the young stars studied (giants and Cepheids) were born from galactic gas, the team suspects that the wave not only carries the stars, but also the gas itself from the disk. The stars would have simply inherited the motion of the gas from which they formed, preserving a “memory” of the wave.
Now the investigation must continue. Astronomers are looking forward to Gaia’s fourth data release, which will provide even more precise measurements and help create detailed maps to perhaps finally reveal the origin of our galaxy’s undulating heart.
Images | Dns Dgn
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