The Hubble Space Telescope:
Time Machine to
A close-up from the
Hubble Ultra Deep Field
Galaxies, galaxies everywhere — as far as
the Hubble Space Telescope can see. Galaxies are large collections
of stars, gas, and dust
held together by gravity. The Earth-orbiting observatory looked
far back in time to find as many as 10,000 galaxies. Many are
different colors, shapes, sizes, and ages. Most of them existed
before the Earth was born. Some were formed just a short time
after the universe was created some 13.7 billion years ago.
This stunning view of the universe is called the Hubble Ultra
Deep Field (HUDF). The image is the farthest view of the universe
ever taken in visible light.
How far is far?
Light from these faraway galaxies began traveling to Earth
billions of years ago, long before humans roamed our planet.
On Earth, we see the light from a lamp the moment we turn it
on because light travels extremely fast. Light from the distant
galaxies in the Hubble Ultra Deep Field travels at the same
speed. Those galaxies are so far away, however, that it takes
a long time for their light to reach Earth. We see the galaxies,
therefore, as they appeared billions of years ago.
How to hook a galaxy
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The zoomable HUDF: You're
the driver — take a tour of the complete HUDF
How do astronomers study these very distant galaxies? Imagine standing on a beach, casting for fish in the surf. You catch a few small- and medium-size fish. Now imagine standing on a boat in the middle of the ocean, where the water is a hundred feet deep. Once again, you are casting for fish. You catch more fish, but these fish look different from those you caught on the beach. When you combine both catches, you see fish of many different colors, shapes, sizes, and ages.
Into the deep
HUDF reveals stages of
Think of astronomers as galactic fishermen. They are casting
for the variety of galaxies that reside deeper and deeper in
space. To look deeper in space astronomers must use powerful
telescopes like the Hubble Space Telescope. As astronomers
gaze farther into space, they see younger and younger galaxies.
In fact, the galaxies look different the farther back in time
the astronomers look. There are no beautiful spiral and elliptical
galaxies like those we see in the neighborhood of our Milky Way galaxy.
Instead, astronomers see oddly shaped blobs that are the building
blocks of galaxies, and galaxies that have become distorted
from collisions with other galaxies.
Galaxies shed light on
the history of the universe
Astronomers hope to look even deeper in space to a time when there were no galaxies. The absence of galaxies means that the universe was so young that galaxies had not had time to form. By looking at galaxies stretching farther and farther back in time, astronomers have learned that galaxies change over time. They are putting together the snapshots of galaxies over many different eras so that they can tell a more complete story of how galaxies form and change. This information will help astronomers understand how the universe began and where it is heading.