Infrared astronomy

Difference between visible and infrared light in the Hat Galaxy or Messier 104.

Infrared astronomy is the study of astronomical sources based on the infrared radiation they emit. For this, infrared spectroscopy is used.

Although in general, infrared is called electromagnetic radiation with a wavelength longer than that of visible light (400-700 nm) and shorter than that of terahertz radiation (100-1000 μm) or microwaves (1-1000 mm), in astronomy the range between 1 and 1000 micrometers is usually considered as infrared. This range is further subdivided into 3 or 4 intervals:

• Nearly 1 to 5 μm infrared
• Average infrared from 5 to 25-40 μm
• Infrared from 25-40 to 200-350 μm
• Submillimeter 200-350 μm to 1 mm (some include in the range of radio waves)

This subdivision has its raison d'être in the different physical phenomena that are observable in each of these ranges, as well as in the different observation techniques and detector technology used in each of them.

The Earth's atmosphere absorbs radiation from astronomical sources in almost the entire infrared spectrum (from 1 to 1000 μm), except for a few atmospheric transmission windows in which it partially transmits, and also emits strongly in the infrared, therefore that infrared observation from the ground requires techniques that allow the elimination of the contribution of the atmosphere. For this reason, the largest infrared radiation telescopes are built on top of very high mountains, installed in special high-altitude airplanes, in balloons, or better still, in Earth-orbiting satellites.

Because infrared radiation is less absorbed or deflected by cosmic dust than shorter-wavelength radiation, regions obscured by dust in visible or ultraviolet light can be seen in infrared. Among the regions that are most effectively studied in the infrared are the galactic center and the star-forming regions.

Infrared observations reveal cold states of matter

Solid objects in space—from the size of an interstellar dust grain, less than a micron, to giant planets—have temperatures ranging from 3 to 3,000 kelvins (K). Most of the energy radiated by objects in this temperature range is in the infrared. Infrared observations are therefore of particular importance in the study of low-temperature media, such as dusty interstellar clouds where stars are forming, as well as the icy surfaces of planetary satellites and asteroids.

Infrared observations explore the hidden universe

Cosmic dust grains obscure parts of the Universe, blocking light from critical regions. This dust becomes transparent in the near infrared, where observers can study optically invisible regions such as the center of our Galaxy (and other galaxies) and dense clouds where stars and planets are being born. For many objects, including stars in dusty regions, active galactic nuclei, and even entire galaxies, the visible radiation absorbed by dust and re-emitted in the infrared constitutes the majority of their luminosity.

Infrared observations provide access to many spectroscopic lines

The emission and absorption bands of virtually all molecules and solids lie in the infrared, where they can be used to study the physical and chemical conditions of relatively cold environments. Many atoms and ions have spectral lines in the infrared, which can be used to study stellar atmospheres and interstellar gas, exploring regions that are too cold or too dusty to be studied in visible light.

Infrared observations study the young universe

The cosmic redshift, which results from the general expansion of the Universe, shifts energy inexorably towards long wavelengths, the shift being proportional to the distance from the object. Due to the finite speed of light, objects with a large redshift are observed as they were when the Universe was much younger. As a result of the expansion of the Universe, most of the optical and ultraviolet radiation emitted by stars, galaxies, and quasars since the beginning of time is now in the infrared. How and when the first objects in the Universe formed will be largely explained by infrared observations.

Space observatories

Because the transmission of the atmosphere in the infrared is limited to some windows, and even in them, the transparency depends on the amount of water vapor through which the light has to pass, telescopes to observe in the infrared must be located in dry places and at high altitude.

Among the places where these conditions are met are Mauna Kea, in Hawaii, United States, where there are a large number of telescopes, and Paranal in the Antofagasta region, Chile, site of the VLT, Very Large Telescope of the ESO, European Southern Observatory.

Even better is to use space-based observatories, which can see into regions where Earth's atmosphere is completely opaque. Among the most important past missions are IRAS and the Infrared Space Observatory. Today, highlights include the NICMOS camera on the Hubble Space Telescope, the Spitzer Space Telescope, launched in 2003, and the James Webb Space Telescope. In the coming years, it is planned to launch the Herschel Space Observatory, focused on the study of infrared.

Most of the article was obtained from https://web.archive.org/web/20030829072815/http://sirtf.caltech.edu/espanol/ciencia/porque.shtml, public domain