The Infrared Universe
THE EARLY UNIVERSE
In the infrared, astronomers can gather information about the universe as it was a very long time ago and study the early evolution of galaxies. Although light travels extremely fast (186,000 miles per second) the universe is so incredibly vast that it can take up to billions of years for light to reach us. The farther away an object is, the farther in the past we see it. For example, it takes light about 8 minutes to reach us from our Sun, so solar astronomers see the Sun as it was 8 minutes ago. If a large flare started this second, they would not see it for another 8 minutes. Light from the nearest star takes about 4.3 years to reach us, and light from the center of our own galaxy takes about 25,000 years to reach us. The billions of galaxies outside our own galaxy range in distance from hundreds of thousands to billions of light years away. For the most distant galaxies, we see them as they were billions of years ago.
As a result of the Big Bang (the tremendous explosion which marked the
beginning of our Universe), the universe is expanding and most of the
galaxies within it are moving away from each other. Astronomers have
discovered that all distant galaxies are moving away from us and that the
farther away they are, the faster they are moving. This recession of galaxies
away from us has an interesting effect on the light emitted from these
galaxies. When an object is moving away from us, the light that it emits is
"redshifted". This means that the
of light get longer and are
shifted towards the red part of the spectrum.
This effect, called the Doppler effect, is similar to what happens to sound
waves emitted from a moving object. For example, if you are standing
next to a railroad track and a train passes you while blowing its horn,
you will hear the sound change from a higher to a lower frequency as
the train passes you by.
As a result of this Doppler effect, at large redshifts,
visible light from distant sources is shifted into the infrared part of the
spectrum. This means that infrared studies can give us much information about
the visible spectra of very young, distant galaxies.
The image on the left is an infrared view of some of the farthest galaxies
ever seen. It was taken by the Hubble Space Telescope's NICMOS camera.
Some of the galaxies shown here were previously unknown.
In 1965, the radiation left over from the Big Bang was discovered by radio astronomers Arno Penzias and Robert Wilson. This radiation, which peaks at 3 degrees Kelvin (-454 degrees Fahrenheit) can be found in all directions in space. Astronomers believe that this radiation was much hotter in the past and that it should behave like a "blackbody" (an object that is perfectly black because it absorbs all of the electromagnetic radiation that reaches it). To prove this, additional data were needed. In 1975, infrared observations made from a balloon flight proved that the Cosmic Background Radiation follows a blackbody curve. Additional studies of the Cosmic Background Radiation were done using the COBE satellite which was launched in 1989. COBE discovered that the background radiation is not entirely smooth and shows extremely small variations in temperature. These small temperature differences may be due to variations in the density of the early universe which may have led to the formation of galaxies.
Infrared studies have also found a potential protogalaxy
(a galaxy in the process of formation) more than 15 billion light years from
Earth. This object, named IRAS 10214+4724, may be a huge, contracting
hydrogen cloud just beginning to shine with newborn stars. This is close to
the edge of the observable universe and its light has taken since nearly the
beginning of the universe to reach us. Protogalaxies provide us with a look
at the era when galaxies were first coming to life.