Contact with another galaxy likely left a vast ripple in Milky Way

The Milky Way seems to harbour a vast ripple spreading out across at least a quarter of its disc. But scientists have never confirmed it and some say that it doesn't exist at all. However, if it is present, then it might have been created following a clash with another galaxy.

Eloisa Poggio at the French National Centre for Scientific Research in Nice and her team say that they have noticed a faint ripple in the galaxy that is propagating away from its centre. "It’s not huge, it’s just a small ripple,” Poggio told New Scientist.

The team made the observation after studying the motion of tens of thousands of stars using the Gaia space telescope. Previously, a few other waves have also been discovered, but the latest wave spreads out over a vast section of the galaxy, she says.

The Milky Way appears like a flat disc with a bulge at the centre in illustrations. However, scientists have noticed small waves in small portions of the galaxy that seem to have been made by clouds of stars and gas. The disc is warped in a static S-shape.

Poggio and her colleagues studied two groups of stars to know more about waves in the galaxy. Two different groups of young stars that formed recently were seen moving with their surroundings. They compared the vertical and horizontal positions of these two groups of stars, along with their movement, with a model of the galaxy. The shape of the model used had a static S-shaped warp.

Also Read:Earth hit by hundreds of meteorites originating from only 5 craters on Mars

What did the study find?

They noticed two distinct ways the group of stars were moving - back and forth along the radial axis of the galaxy and up and down. However, the two motion patterns were statistically related. The researchers concluded that the two motions are likely part of one vast wave. What caused the ripple is not clear, although Poggio suggests that it could have happened after a past close encounter with a smaller galaxy’s gravity.

However, other experts say they don't see a link between the two motions. Ralph Schoenrich of University College London told New Scientist that instead of one vast wave, there could be two waves.

The groups of stars are moving horizontally and vertically, which means the two waves could be moving in the same way as well. One or more past events likely caused the waves, although he says there is no way to say with certainty that they are part of one wave.

More research is needed to understand more about the observations.