Lessons Overview : Radio Sources II
Radio galaxies are another area of interest to radio astronomers. While all galaxies emit radio waves, some galaxies emit millions of times more radio energy than others. Typically, a radio galaxy will have a tiny optical component at the center (the actual galaxy), with two enormous radio jets on either side. The jets can extend for millions of light years out into space. Optical astronomy shows no indication of their presence, but the radio jets are often the most interesting features of their galaxies.When the jets of a radio galaxy happen to be pointed towards Earth, they are received here as extremely strong sources of radiation. Radio galaxies in this particular orientation are called quasars (quasi-stellar radio sources, or QSRs). Quasars were originally thought to lie inside our galaxy because they emit so much radiation. With further study, it became apparent that they are actually some of the farthest objects ever observed, some of them lying 15 billion light years away and moving away from us at 90% of the speed of light! Quasars and other radio galaxies are part of a class of objects known as active galaxies that emit a large amount of radiation across the entire electromagnetic spectrum, usually in jets.
It is thought that these jets are fueled by radiation from matter falling into massive black holes at the centers of these galaxies. There is some evidence that black holes may exist at the centers of normal galaxies, like our own Milky Way. Sagittarius A, a strong radio source in the center of our galaxy, is most likely a black hole.
Radio galaxy Cygnus A in optical and radio
We acknowledge the use of NASA's SkyView facility located at NASA Goddard Space Flight Center
Sagittarius A in optical and radio
David Talent / NOAO / AURA / NSF
We acknowledge the use of NASA's SkyView facility located at NASA Goddard Space Flight Center
Sagittarius A in optical and radio
David Talent / NOAO / AURA / NSF