The Hydra Cluster.

The Hydra Cluster.

Three-color JHKs composite Atlas Image mosaic,covering 1 1 on the sky of the Hydra Cluster of galaxies, aka Abell (ACO) 1060. More than a hundred galaxies are seen clustered toward the southern constellation Hydra. The "haloes" around the infrared bright Milky Way foreground stars (HD 92036, a M-type giant to the northeast, and HD 91964, a K-type giant to the southwest; the halo of the brighter star is truncated, due to the 2MASS scan edge) dominate the image. But, compare this 2MASS image with an optical image: In the near-infrared, the optical veneer of recently-formed hot, bright blue stars, the gaseous nebulae, and dark lanes of dust in the cluster's galaxies is stripped away to reveal the bulk of the galaxies' mass, namely, the cool, lower-mass stars. Because these stars have existed for a much longer time and have had time to move away from their birthplaces within the galaxies, the distribution of their infrared light is quite smooth.

The morphology for galaxies of different Hubble type (spirals and ellipticals) therefore is more similar in the near-infrared than in the optical. (N.B.: The full mosaic is 13.6 Mb in size! A smaller, 4 4-binned, 852-kb version of the mosaic can be obtained here.)

Image mosaic by T. Jarrett (IPAC).