Cores Jets and Lobes Radio Galaxy Anatomy

Another kind of active galaxy is called a radio galaxy. While Seyferts are an active subclass of spiral galaxies, what we call radio galaxies are an active subclass of elliptical galaxies.

There are many types of radio galaxies, often classified by their shapes. Some radio sources have emission only in their nucleus. In others, two narrow streams— or jets—of oppositely directed radio emission emerge from the galaxy nucleus. The jets in these so-called double radio sources often end in wispy, complex puffs of radio emission much larger than the central elliptical galaxy. These are called radio lobes. In some radio galaxies the lobe emission dominates, and in others the jet emission dominates.

One remarkable aspect of the jets of radio emission is that they are observed over such a huge range of scales. The jets in some galaxies are linear for hundreds of thousands of light-years, and yet are observable down to the smallest scales that we can see—a few light-years. Radio jets are thought to be beams of ionized material that have been ejected from near the galactic center. The jets eventually become unstable and disperse into lobes.

The radio galaxy 3C31 is shown superimposed on an optical image of the same region. In the inset to the right, the VLA image (jets) is superimposed on a Hubble Space Telescope image of the region. World-class telescopes need to improve their resolutions in sync so that overlays like these are possible.

(Image from NASA)

Star Words

Radio galaxies are an active galaxy subclass of elliptical galaxies. They are characterized by strong radio emission, and in some cases, narrow jets and wispy lobes of emission located hundreds of thousands of light-years from the nucleus.

Star Words

Radio galaxies are an active galaxy subclass of elliptical galaxies. They are characterized by strong radio emission, and in some cases, narrow jets and wispy lobes of emission located hundreds of thousands of light-years from the nucleus.

Close Encounter

Many differences in astronomy come down to a question of perspective. Astronomers are not entirely certain that core-halo radio galaxies (with a bright center and a diffuse envelope of emission) and lobe radio galaxies (with a distinct bright center and diffuse lobes) are unique objects. That is, a core-halo galaxy may be nothing more than a foreshortened view of a lobe radio galaxy. If the galaxy happens to be oriented so that we view it through the end of one of its lobes, it will look like a core-halo galaxy. If we happen to see the galaxy from its side, two widely spaced radio lobes will be detected on either side of a central core.

Material in radio jets is being accelerated to enormous velocity. In some radio jets, bright blobs of radio emission appear to be moving faster than light. And that's not allowed!

What's going on? The apparent superluminal motion (speed faster than light) results from jets that are moving toward us. It does not defy any laws of physics.

What is this mysterious radio emission we have been comes in two basic flavors. One is rather bland, and bland radio emission is thermal emission, which arises most commonly in regions of hot, ionized gas—like the HII ("H-two") regions around young, massive stars. This type of radio emission comes from free electrons that are zipping around in the hot gas.

The spicy variety is synchrotron emission, sometimes called non-thermal emission. This type of radiation arises from charged particles that are being accelerated by strong magnetic fields. (James Clark Maxwell first discussed the effects of magnetic fields on charged particles.) The intensity of synchrotron radiation is not tied to the temperature of the source, but to the strength of the magnetic fields that are there. Radio jets, filled with charged particles and laced with strong magnetic fields, are intense sources of synchrotron radiation.

discussing? Well, radio emission the other a bit more spicy. The

Superluminal motion is a term for the apparent "faster than light" motion of the blobs in some radio jets. This effect results from radio-emitting blobs that are moving at high velocity toward us.

Star Words

Superluminal motion is a term for the apparent "faster than light" motion of the blobs in some radio jets. This effect results from radio-emitting blobs that are moving at high velocity toward us.

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