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hubie writes:

Mysterious ripples in the Milky Way were caused by a passing dwarf galaxy:

Using data from the Gaia space telescope, a team led by researchers at Lund University in Sweden has shown that large parts of the Milky Way's outer disk vibrate. The ripples are caused by a dwarf galaxy, now seen in the constellation Sagittarius, that shook our galaxy as it passed by hundreds of millions of years ago.

[...] "We can see that these stars wobble and move up and down at different speeds. When the dwarf galaxy Sagittarius passed the Milky Way, it created wave motions in our galaxy, a little bit like when a stone is dropped into a pond", Paul McMillan, the astronomy researcher at Lund Observatory who led the study, explains.

[...] The researchers were surprised by how much of the Milky Way they could study using the data from Gaia. To date the telescope, which has been in operation since 2013, has measured the movement across the sky of approximately two billion stars and the movement towards or away from us of 33 million.

"With this new discovery, we can study the Milky Way in the same way that geologists draw conclusions about the structure of the Earth from the seismic waves that travel through it. This type of "galactic seismology" will teach us a lot about our home galaxy and its evolution", Paul McMillan concludes.

Journal Reference:
Paul J McMillan, Jonathan Petersson, Thor Tepper-Garcia, et al., The disturbed outer Milky Way disc [open], MNRAS, Volume 516, Issue 4, November 2022, Pages 4988–5002. DOI: 10.1093/mnras/stac2571

Original Submission