Milky Way Disk Tilt and Andromeda Star‑Formation Slowdown Uncovered by New Studies

Astronomers at the University of Durham in the United Kingdom used supercomputer simulations together with data from the European Space Agency’s Gaia mission to show that the Milky Way’s stellar halo rotates very slowly, making its disk susceptible to a dramatic re‑orientation of more than 90 degrees. The work suggests the tilt resulted from an ancient head‑on merger with a dwarf galaxy known as Gaia‑Sausage‑Enceladus about 10–11 billion years ago, reshaping the Galaxy’s structure.

In a separate analysis, a team led by Tobin Wainer of the University of Washington examined Hubble Space Telescope observations of the neighboring Andromeda galaxy. Their measurements indicate the galaxy’s star‑formation rate has fallen by roughly 80 % over the last 40 million years, dropping from about one solar mass per year to a fifth of that. The decline appears to be a natural slowdown after a more active epoch, with the satellite galaxy M32 possibly contributing to the reduced activity.