Spiral Arms Embrace Young Star - News & Columns - ALMA NAOJ
http://alma.mtk.nao.ac.jp/e/news/info/2016/0930spiral_arms_embrace_young_star.html
Swirling around the young star Elias 2-27, astronomers discovered a stunning spiral-shape pinwheel of dust. This striking feature,
seen with the Atacama Large Millimeter/submillimeter Array (ALMA), is the product of density waves—gravitational perturbations in
the star's protoplanetary disk that produce sweeping arms reminiscent of a spiral galaxy, but on a much smaller scale.
"These observations are the first direct evidence for density waves in a protoplanetary disk," said Laura Pérez, an astronomer and
Alexander von Humboldt Research Fellow with the Max Planck Institute for Radio Astronomy in Bonn, Germany, and lead author on a paper
published in the journal Science.