View of Distant, Faint Galaxies Reveals Young Galaxy Building Blocks

Embedded in this Hubble Space Telescope image of nearby and distant galaxies are 18 young galaxies or galactic building blocks, each containing dust, gas, and a few billion stars. Each of these objects is 11 billion light-years from Earth and much smaller than today's galaxies.

At this distance, the universe was only about 16 percent of its current age. The 18 young galaxies were found within an area about 2 million light-years across, which is about the distance between our Milky Way and the Andromeda galaxy. Some astronomers believe the young objects are the ancient building blocks of today's galaxies, because they are close enough in space to eventually collide or merge with each other. At 2,000 to 3,000 light-years across, each building block is larger than a normal star cluster - as seen in our galaxy - but smaller than a present-day galaxy, which typically is about 30,000 to 100,000 light-years wide. They are located in a small region of sky in the northern part of the constellation Hercules, near the border of Draco. The image covers a diameter that is 13 times smaller than that of the full moon.

This picture is a true color image made from separate exposures taken in blue, green, and far-red light with the Wide Field Planetary Camera 2. It required 48 orbits around the Earth (more than one day of exposure time) to make the observation. The green and red exposures were taken in June 1994; the blue exposures, as well as 15 orbits of the redshifted hydrogen line, were taken in June 1995. Compared to the best ground-based observing sites, the sky seen from Hubble's orbit is 2.5 to 15 times darker, and the resolution of this image is about 10 times better. The faintest objects visible in this image are 2 billion times fainter than what the unaided eye can see from a dark location on Earth.