杏吧原创

Are the spiral arms of galaxies evidence for gravitational waves? If not, what creates these arms?

Steve Miall, Higher Poynton, Cheshire, UK

We pay 拢25 for every answer published in New 杏吧原创. To answer this question 鈥� or ask a new one 鈥� visit newscientist.com/lastword. Terms and conditions apply.

This article appeared in print under the headline 鈥淕alaxy twirl鈥�