Compass and Scale Image for Galaxy Cluster MACS J0416.1-2403
These two Hubble Space Telescope images reveal an array of faraway galaxies, many of which existed at least 12.9 billion years ago and earlier. The circles pinpoint the most distant galaxies.
The images were taken simultaneously by two of Hubble's science instruments. The image at left, taken in near-infrared light by the Wide Field Camera 3, shows a very massive cluster of galaxies, called MACS J0416.1-2403, the large, bright galaxies at the center of the image. The cluster's immense gravitational field magnifies and brightens the images of faint galaxies far behind it, in a phenomenon called gravitational lensing.
The image at right, taken in visible light by the Advanced Camera for Surveys, is a parallel field. This view reveals myriad galaxies that make up a general background population, not compacted into a galaxy cluster.
Astronomers examined these Hubble images, along with observations taken in near-infrared light with the Spitzer Space Telescope, to determine the distances of the reddest-looking galaxies. Their light is stretched by the expansion of the universe. So the redder a galaxy looks, the farther away it is. These very dim objects may be more representative of the early universe, and offer new insight on the formation and evolution of the first galaxies.