Giant galaxies like the Milky Way grew by absorbing smaller ones. So why don’t these goliaths become even larger than they do? A new clue comes from high-resolution radio observations of NGC 253 (shown), an edge-on spiral galaxy just 11 million light-years from Earth and the largest member of the so-called Sculptor galaxy group. NGC 253, a giant that’s somewhat smaller than the Milky Way, is experiencing a starburst: For its size, it’s converting gas and dust into new stars at a rapid clip, 2.8 solar masses per year. But as astronomers report online today in Nature, the galaxy is losing more gas than this—between three and 30 solar masses per year—as winds, radiation pressure, and supernova explosions from the starburst itself drive gas away. Because gas is the raw material for creating stars, NGC 253 is literally jettisoning its chances to be as big as it could be; but it’s also giving astronomers a ringside seat on a phenomenon that probably puts a lid on galaxy growth throughout the universe.
| image ESO