Four Spiral Galaxies, From Ground (upper) and Hubble (lower)
Astronomers have combined information from the NASA Hubble Space Telescope's visible- and infrared-light cameras to show the hearts of four spiral galaxies peppered with ancient populations of stars. The top row of pictures, taken by a ground-based telescope, represents complete views of each galaxy. The blue boxes outline the regions observed by the Hubble telescope.
The bottom row represents composite pictures from Hubble's visible- and infrared-light cameras, the Wide Field and Planetary Camera 2 (WFPC2) and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS). Astronomers combined views from both cameras to obtain the true ages of the stars surrounding each galaxy's bulge. The Hubble telescope's sharper resolution allows astronomers to study the intricate structure of a galaxy's core.
The galaxies are ordered by the size of their bulges. NGC 5838, an "S0" galaxy, is dominated by a large bulge and has no visible spiral arms; NGC 7537, an "Sbc" galaxy, has a small bulge and loosely wound spiral arms. Astronomers think that the structure of NGC 7537 is very similar to our Milky Way.
The galaxy images are composites made from WFPC2 images taken with blue (4445 Angstroms) and red (8269 Angstroms) filters, and NICMOS images taken in the infrared (16,000 Angstroms). They were taken in June, July, and August of 1997.
Credits for the ground-based images: Allan Sandage (The Observatories of the Carnegie Institution of Washington) and John Bedke (Computer Sciences Corporation and the Space Telescope Science Institute)