Viewed in visible light, the elliptical galaxy NGC 4261 looks positively sedate. But a new X-ray image reveals evidence of a violent past–a trail more than 50 light-years across and rife with black holes and neutron stars. The trail indicates that the galaxy collided with another galaxy a few billion years ago, says Lars Hernquist of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
He and his colleagues say that the image, recorded by NASA's Chandra X-ray Observatory, suggests that X-ray studies may be the best way to identify ancient collisions between galaxies. The researchers report their findings in the Dec. 20, 2003 Astrophysical Journal Letters.