The radio to X-ray continuum shape of quasars (gif), (Elvis et al., 1994, ApJS, 1. Plotted in log nufnu vs log nu (nu=frequency) space. Solid line = radio-quiet; dashed line = radio-loud.
X-axis (bottom): log frequency in Hertz (cycles/second).
X-axis (top): frequency in centimeters (cm), millimeters (mm), microns (mu), Angstroms (A) and kilovolts (keV). [Mixed units are normal, if annoying, in astronomy, as we strive to keep the numbers comprehensible in each waveband.]
Horizontal line: shows equal power per decade [or octave, or any equal sized division in log(nu)]. A quasar keeps its power output almost constant from the far-infrared (100mu) to X-rays (10keV), with excursions of only a factor of a few.
Observing bands in Green: Radio= radio; IR=infrared; Opt-UV = optical and ultraviolet; EUV = extreme ultraviolet; X-ray = X-ray.
Radio-loud, Radio-quiet: quasars that look virtually identical at all other wavelengths can differ by a 1000 in their radio emission. Radio-loud quasars have a powerful jet moving at relativistic speeds (i.e. close to the speed of light) made up of energetic particles, themselves moving near the speed of light in a magnetic field. This causes them to radiate light by the synchrotron process.
Big Blue Bump: This feature dominates the quasar emission by a modest factor. It is likely due to emission from an accretion disk around the central supermassive black hole that has a range of temperatures from ~100,000K to ~1000K.