Faint Blue Sub-Galactic Clumps May Be Galaxies Under Construction
These 18 small blue objects - each 11 billion light-years from Earth - could be the seeds of some of today's galaxies. Each clump contains several billion stars. Astronomers believe that many of these objects have collided and merged with each other over time to grow into the giant and luminous galaxies seen around us today.
The Hubble Space Telescope found these objects through the light of their hydrogen atoms. This light was redshifted from ultraviolet wavelengths to visible light, due to the expansion of the universe. Ground-based spectroscopic observations for 10 of these objects yielded confirmations of their distances thus far. Each object is 2,000 to 3,000 light-years across, and was found in an area about 2 million light-years wide. This area is comparable to the distance between our Milky Way galaxy and its nearest luminous neighbor, the Andromeda galaxy. The number of sub-galactic-size objects is significantly higher than that of the luminous galaxies seen today in a similar volume of space. These 18 objects are located in a small region of the sky in the northern part of the constellation Hercules, near the border of Draco. At the objects' distance, each postage stamp-sized image shown here is about one-third of our galaxy's diameter. Our Milky Way galaxy, which is about 100,000 light-years across, would occupy several of these boxes.
Each image is a true color display made from separate exposures taken in blue, green, and far-red light with the Wide Field Planetary Camera 2. The telescope made the observation during 48 orbits around the Earth (more than one day of exposure time). 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.