Hubble Uncovers One of the Smallest and Farthest Galaxies in the Universe

The heart of the mammoth galaxy cluster Abell 2744, also known as Pandora's Cluster, is shown in this Hubble Space Telescope image. The cluster is so massive that its powerful gravity bends the light from galaxies far behind it, making background objects appear larger and brighter in a phenomenon called gravitational lensing. These powerful lenses allow astronomers to find many dim, distant structures that otherwise might be too faint to see.

The small white boxes, labeled "a," "b," and "c," mark multiple images from the same background galaxy, one of the farthest, faintest, and smallest galaxies ever seen. The diminutive object is estimated to be over 13 billion light-years away. Enlarged views of the multiple images are shown in the insets at right. The arrows point to the tiny galaxy far behind the cluster. Each magnified image makes the galaxy appear as much as 10 times larger and brighter than it would look without the intervening lens.

To determine the background galaxy's distance, the researchers studied the galaxy's color and measured the positions between the three images. This new detection is considered one of the most reliable distance measurements of a galaxy that existed in the early universe. The galaxy appears as a tiny blob that is only a small fraction of the size of our Milky Way galaxy. But it offers a peek back into a time when the universe was only about 500 million years old, roughly 3 percent of its current age of 13.7 billion years.

An analysis of the distant galaxy shows that it measures merely 850 light-years across, 500 times smaller than the Milky Way, and is estimated to have a mass of only 40 million suns. The galaxy's star formation rate is about one star every three years (one-third the star formation rate in the Milky Way).

The galaxy was detected as part of the Frontier Fields program, an ambitious three-year effort, begun in 2013, that teams Hubble with NASA's other Great Observatories – the Spitzer Space Telescope and the Chandra X-ray Observatory – to probe the early universe by studying large galaxy clusters. Abell 2744 resides about 3.5 billion light-years away.

The image was made by combining near-infrared observations from Hubble's Wide Field Camera 3 and visible-light exposures from the Advanced Camera for Surveys. The observations were taken in 2009, 2013, and 2014.