The mesmerizing outskirts of NGC 4603 – a key galaxy in Hubble’s ‘key project’

The outskirts of the galaxy NGC 4603 are packed with a sea of stars as imaged by the Hubble Space Telescope. NGC 4603 was one of 18 galaxies studied in detail for one of Hubble’s first major projects, a search for Cepheid variable stars at greater distances than previously resolved to help pin down the Hubble constant and thus the age of the universe. The “key project” found some 800 Cepheids in far-flung galaxies, allowing astronomers to determine, with an uncertainty of 10 percent, that the universe was approximately 12 billion years old. Subsequent research pushed the age back to 13.8 billion years with an uncertainty of just 20 million years or so. NGC 4603 is about 108 million light years from Earth in the constellation Centaurus.

NGC 4603. Image: ESA/Hubble & NASA, J. Maund