Infrared astronomy involves the use of telescopes that detect electromagnetic radiation (radiation that transmits energy through the interaction of electricity and magnetism) at infrared wavelengths. Infrared astronomy has led to the discovery of many new stars, galaxies, asteroids, and quasars.
Light is a form of electromagnetic radiation. The different colors of light that human eyes can detect correspond to different wavelengths of light. Red light has the longest wavelength; violet has the shortest. Orange, yellow, green, blue, and indigo have wavelengths in between. Infrared light, ultraviolet light, radio waves, microwaves, and gamma rays are all forms of electromagnetic radiation, but they differ in wavelength and frequency.
Infrared light has slightly longer wavelengths than red light. Human eyes cannot detect infrared light, but people can feel it as heat.
Infrared telescopes can operate on the ground or from space. The use of ground-based telescopes is somewhat limited because carbon dioxide and water in the atmosphere absorb much of the incoming infrared radiation. The best observations are made at high altitudes in areas with dry climates. Since infrared telescopes are not affected by light, they can be used during the day as well as at night.
Space-based infrared telescopes pick up much of the infrared radiation that is blocked by Earth’s atmosphere. In the early 1980s, an international group made up of the United States, United Kingdom, and The Netherlands launched the Infrared Astronomical Satellite (IRAS). Before running out of the liquid helium that the satellite used to cool its infrared detectors in 1983, IRAS uncovered never-before-seen parts of the Milky Way, the galaxy that is home to our solar system.
In 1995, the European Space Agency launched the Infrared Space Observatory (ISO), anastronomical satellite. Before it ran out of liquid helium in 1998, the ISO discovered protostars, planet-forming nebulae around dying stars, and water throughout the universe, including in gas giants such as the planets Saturn and Uranus.
On August 25, 2003, the National Aeronautics and Space Administration (NASA) launched the Spitzer Space Telescope (formerly known as the Space Infrared Telescope Facility, or SIRTF), designed to search for infrared radiation that is otherwise blocked by Earth's atmosphere. It ran out of liquid helium in 2009. It found light from extrasolar planets, discovered some very new stars, and found the Double Helix Nebula at the center of the Milky Way.
In 2010 NASA and the German Aerospace Center launched the Stratospheric Observatory for Infrared Astronomy. This telescope is housed inside a Boeing 747 airplane. It has been used to study the formation of stars and planets such as Jupiter.
Discoveries with Infrared Telescopes
Infrared telescopes have helped astronomers find regions of the universe where new stars are forming, clouds of gas and dust called nebulae, or sometimes stellar nurseries. Forming and newly formed stars are still enshrouded by a cocoon of dust that blocks visible light. Infrared astronomers can more easily probe these stellar nurseries than optical astronomers can. The view of the center of our galaxy is also blocked by large clouds of interstellar dust. The galactic center is more easily seen by infrared than by optical telescopes.
With the aid of infrared telescopes, astronomers have also located a number of new galaxies, many too far away to be seen by visible light. Some of these are dwarf galaxies, which are more plentiful but contain fewer stars than visible galaxies. The discovery of these infrared dwarf galaxies has led to the theory that they once dominated the universe and then came together over time to form visible galaxies, such as the Milky Way.
With the growing use of infrared astronomy, scientists have learned that galaxies contain many more stars than had ever been imagined. Infrared telescopes can detect radiation from relatively cool stars, which give off no visible light. Many of these stars are the size of the Sun. These discoveries have drastically changed scientists’ calculations of the total mass in the universe.
Infrared detectors have also been used to observe far-away objects such as quasars. Quasars have large redshifts, which indicate that they are moving away from Earth at high speeds. In a redshifted object, the waves of radiation are lengthened and shifted toward the red end of the spectrum. Since the redshift of quasars is so great, their visible light gets stretched into infrared wavelengths. While these infrared wavelengths are undetectable with optical telescopes, they are easily viewed with infrared telescopes.
In May 2008, an international team of infrared astronomers showed that because of dust drifting between the stars, galaxies are actually about twice as bright as they seem when viewed through telescopes. The dust absorbs about half of all the visible light emitted from stars and reradiates that energy as infrared light.