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Radio Galaxies

Radio Emission Radio galaxies are so named because they are powerful sources of radio emission that radiate much more strongly at radio wavelengths than do conventional galaxies as shown in the upper diagram of Figure 05-04. Whereas normal galaxies emit blackbody radiation, the radio emission is generated by a mechanism called synchrotron radiation. Cygnus A was the first radio galaxy identified in 1951. It is shown in the lower diagram of Figure 05-04. In a typical radio galaxy, most of the emission comes from two huge lobes located far beyond and on either side of the visible galaxy. The radio-emitting lobes are believed to be clouds of energetic charged particles that have been expelled from the nucleus of the central galaxy, the jets are streams of additional energetic particles, which have been accelerated in the nucleus and are surging outward toward the lobes, producing "hot spots" (represented by red colour) where they plow into the leading edges of the lobes.
Radio Emission This material typically spans a region of space five to ten times larger than the visible galaxy, and sometimes far larger than that. The overall luminosities can be up to several thousand times that of the Milky Way. Strong radio emissions are usually associated with elliptical galaxies - such as M87 (Virgo A) - or disturbed galaxies such as Centaurus A. This kind of objects is sometimes referred to as AGN for Active Galaxy Nucleus. By superimposing the radio images taken by the Very Long Baseline Array (VLBA) to the gamma-ray sky map produced by the Large Area Telescope (LAT), astronomers are able to confirm that the gamma-ray emission from the core of AGN is associated with the radio jet.

Figure 05-04 Radio Galaxy

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