Infrared Astronomy is the detection and study of the
infrared radiation
(heat energy) emitted from objects in the Universe. Every object that has a
temperature radiates in the infrared. So, Infrared Astronomy
involves the study of just about everything in the Universe.
In the field of astronomy, the infrared region lies within the range of
sensitivity of infrared detectors, which is between
wavelengths of about 1 and 300 microns
(a micron is one millionth of a meter).
The human eye detects only 1% of light at 0.69 microns, and 0.01% at 0.75
microns, and so effectively cannot see wavelengths longer than about 0.75
microns unless the light source is extremely bright.
Viewing the Invisible
{see an example of the
invisible becoming "visible" in the infrared}
The Universe sends us a
tremendous amount of information in the form of
electromagnetic radiation
(or light). Much of this information is in the infrared, which we cannot
see with our eyes or with visible light telescopes. Only a small amount of
this infrared information reaches the Earth's surface, yet by studying this
small range of infrared wavelengths, astronomers have uncovered a wealth of
new information. Only since the early 1980's have we been able to send
infrared telescopes into orbit around the Earth, above the atmosphere which
hides most of the Universe's light from us. The new discoveries made by these
infrared satellite missions has been astounding. The first of these satellites
- IRAS
(Infrared Astronomical Satellite) - detected about 350,000
infrared sources, increasing the number of cataloged astronomical sources by
about 70%.
In space, there are many regions which are hidden from optical telescopes
because they are embedded in dense regions of gas and dust.
However, infrared radiation, having wavelengths which are much longer than
visible light, can pass through dusty regions of space without being
scattered.
This means that we can study objects hidden by gas and dust in
the infrared, which we cannot see in visible light, such as the center of
our galaxy and regions of newly forming stars.
Many objects in the universe which are
much too cool and faint to be detected in visible light, can be detected in
the infrared. These include cool stars, infrared galaxies, clouds of
particles around stars, nebulae, interstellar molecules, brown dwarfs and planets.
For example, the visible light from a planet is hidden by the brightness of the star that
it orbits.
In the infrared, where planets have their peak brightness, the brightness of the star is
reduced, making it possible to detect a planet in the infrared.
Some of the most exciting discoveries in infrared astronomy have been the detection
of disks of material and possible planets around other stars.
Recently, an infrared survey of the Trapezium star cluster in the Orion Nebula
revealed over 100 low mass objects which are brown dwarf candidates.
Click on the image for details.
Exploring 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.
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 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 large redshifts, all of the ultraviolet
and much of the visible light from distant sources is shifted into the infrared part of the
spectrum by the time it reaches our telescopes.
This means that the only way to study this light is in the infrared.
Infrared astronomy will provide a great deal of information on how and when
the universe was formed and on what the early universe was like.
The image to the left is an infrared view of some of the farthest galaxies
ever seen. (Image credit:
R.I. Thompson (U. Arizona), NICMOS, HST, NASA)
Adding To Our Knowledge Of Visible Objects
Objects which can be seen in visible light can also be studied in the infrared.
Infrared astronomy can not only allow us to discover new objects and view
previously unseen areas of the universe, but it can add to what we already
know about visible objects.
To get a complete picture of any object in the Universe we need
to study all of the radiation that it emits. Infrared Astronomy
has, and will continue to, add a great
deal to our knowledge about the Universe and the origins of our Solar System.
Exploring the Hidden Universe
Galactic Center
Cygnus Region