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Looking back in time nearly 9 billion years, an international team of astronomers found mature galaxies in a young universe. The galaxies are members of a cluster of galaxies that existed when the universe was only 5 billion years old. This compelling evidence that galaxies must have started forming just after the big bang was bolstered by observations made by the same team of astronomers when they peered even farther back in time. The team found embryonic galaxies a mere 1.5 billion years after the birth of the cosmos. The "baby galaxies" reside in a still-developing cluster, the most distant proto-cluster ever found.

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Q & A: Understanding the Discovery

1. 1. How can telescopes look far back in time?




The light from distant galaxies takes billions of years to travel across space and reach Earth. Observatories like the Hubble telescope are powerful enough to collect the light from faraway galaxies.

2. 2. How do astronomers know the galaxies are far away?




Astronomers analyze the colors of light emitted by these faraway galaxies to estimate the galaxies' distance from Earth. The farther the galaxy, the redder its light will appear. Astronomers then compare the noted color with the color they expected the galaxy to be.

3. 3. What do these galaxies look like today?




Astronomers don't know what these galaxies look like today because it would take billions of years more for the light from the mature galaxies to reach Earth. After all, the light from these galaxies as youngsters has just arrived at Earth. By analyzing the light from the youthful galaxies, which existed when the universe was young, astronomers can predict what these galaxies might look like today. It is like looking at an old snapshot of a long-lost childhood friend. Although you lost touch with this friend years ago, you assume the friend grew up and became an adult.