Free Astronomy Magazine September-October 2025

SEPTEMBER-OCTOBER 2025 A smashup between our own galaxy and Andromeda would trigger a firestorm of star birth, supernovae, and maybe toss our Sun into a dif- ferent orbit. Simulations had sug- gested it was inevitable. However, a new study using data from Hubble and ESA’s Gaia suggests this may not necessarily be the case. Researchers combining observations from the two space observatories re- examined the long-held prediction of a Milky Way – Andromeda colli- sion, and found it is far less in- evitable than astronomers had previously suspected. “We have the most comprehensive study of this problem today that ac- tually folds in all the observational uncertainties,” said Till Sawala, as- tronomer at the University of Helsinki in Finland and lead author of the study, which appears in the journal Nature Astronomy . No certainty of a Milky Way–Andromeda collision by NASA/ESA Bethany Downer A s far back as 1912, astrono- mers realized that the An- dromeda galaxy — then thought to be only a nebula — was headed our way. A century later, as- tronomers using the NASA/ESA Hub- ble Space Telescope were able to measure the sideways motion of An- dromeda and found it was so negli- gible that an eventual head-on collision with the Milky Way seemed almost certain.