Welcome to the World of Multiwavelength Astronomy!
The Multiwavelength Universe
The night sky has always served as a source of wonder and mystery to
people. However, it has only been in the past few decades that we have
truly begun to 'see' the Universe in all its glory. This is because we
have only recently been able to look at the Universe over the entire
electromagnetic spectrum. Our Universe contains objects
which produce a vast range of radiation with wavelengths either too short
or too long for our eyes to see.
Instruments which examine all parts of the electromagnetic (EM) spectrum
have been available to us only in the 20th century, since the rocket age
was required to get instruments sensitive to the infrared, ultraviolet,
X-rays, and gamma-ray wavelengths above the Earth. (This "view from
space" is extremely important since radiation in these wavelengths is
absorbed by the Earth's atmosphere).
Some astronomical objects emit mostly infrared radiation,
others mostly visible light, and still others mostly ultraviolet
radiation. What determines the type of electromagnetic radiation
emitted by astronomical objects? The simple answer is TEMPERATURE!
A solid contains molecules and atoms that are in continuous vibration.
Inside a gas are molecules that are flying about freely at high
rates, continually bumping into each other and surrounding matter. That
energy of motion is called HEAT. The hotter the solid or gas, the more
rapid the motion of the molecules. And temperature is just a measure of
the average energy of those particles.
The optical image of the cosmos seen on the left (top) is courtesy of
the Lund Observatory; the radio image (at 408 MHz; center) is courtesy
of The Max Planck Institute for Radio Astronomy (generated by Glyn
Haslam); the gamma-ray image (bottom) is from the EGRET experiment
on-board the Compton Gamma-Ray Observatory.
What Kinds of Objects Typically Emit What Kinds of Radiation?
Do you want to understand in more detail the relationship between
temperature and electromagnetic radiation (and typical sources that emit
both)? Look at the chart below.
| Type Of Radiation |
Radiated By Objects At This Temperature |
Typical Sources |
|---|
| Gamma-rays |
more than 108 Kelvin (K) | accretion disks around black holes |
| X-rays |
106-108 K |
gas in clusters of galaxies; supernova remnants; stellar corona |
| Ultraviolet |
104-106 K |
supernova remnants; very hot stars |
| Visible |
103-104 K |
planets, stars, some satellites |
| Infrared |
10-103 K |
cool clouds of dust and gas; planets |
| Radio |
less than 10 K |
radio emission produced by electrons moving in magnetic fields |
| 
