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. 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.

Infrared view of some of the farthest galaxies ever seen. Some of the galaxies shown here were previously unknown. (Credit: R.I. Thompson (U. Arizona), NICMOS, HST, NASA)

As a result of the Big Bang (the tremendous explosion which is thought to have 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 wavelengths get longer and thereby 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 very large redshifts, ultraviolet and 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 ultraviolet and visible spectra of very young, distant galaxies.

In 1965, the remnant radiation from the Big Bang was discovered by radio astronomers Arno Penzias and Robert Wilson. This radiation, which peaks at 3 K (-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.

Astronomers using the Spitzer Space Telescope will study dusty protogalaxies being born in the young and distant Universe. By learning about a galaxy's properties at different distances, Spitzer scientists will trace the history of star formation as a function of environment and will try to discover why the rate of star formation was much higher in the past. Spitzer will also be used to confirm the recent detections of the cosmic background radiation and will characterize the source(s) of this radiation.