The ‘Pacman Nebula’

High-mass stars are important because they are responsible for much of the energy pumped into our galaxy over its lifetime. Unfortunately, these stars are poorly understood because they are often found relatively far away and can be obscured by gas and dust. The star cluster NGC 281 is an exception to this rule. It is located about 6,500 light years from Earth and, remarkably, almost 1,000 light years above the plane of the galaxy, giving astronomers a nearly unfettered view of the star formation within it.

This composite image of NGC 281 contains X-ray data from Chandra, in purple, with infrared observations from Spitzer, in red, green, blue. The high-mass stars in NGC 281 drive many aspects of their galactic environment through powerful winds flowing from their surfaces and intense radiation that creates charged particles by stripping electrons off atoms. The eventual deaths of massive stars as supernovas will also seed the galaxy with material and energy.

NGC 281 is known informally as the "Pacman Nebula" because of its appearance in optical images. In optical images the "mouth" of the Pacman character appears dark because of obscuration by dust and gas, but in the infrared Spitzer image the dust in this region glows brightly.

NGC 281 is typically divided into two subregions: the region in the upper middle of the image, which is surrounded by the purple 10-million-degree gas, and a younger region in the lower part of the image. There is evidence that the formation of a cluster, appearing in a beige cloud to the lower right, was triggered by a previous generation of star formation. Also, astronomers have found some isolated star formation on the left side of the image that appears to have been occurring at the same time as star formation in other regions of the cluster. This supports the idea that something externally triggered the "baby boom" of stars in NGC 281.