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The Question

(Submitted January 16, 1998)

I don't know very much about astronomy but I have to do I paper on it for school. I was very confused at your info on Blazars. I would like a simple answer to: What are blazers? Thanks!

The Answer

This is a good question, and it might be good to divide it up into 2 parts: first, what does a blazar look like to astronomers, and second, what is actually going on in a blazar? It turns out that astronomers themselves can't even answer the first question with certainty. I would say that in order to be called a blazar, an object must have the following characteristics:

1) It must appear point-like on the sky, i.e. not appear fuzzy like a galaxy or a nebula. Some blazars have nebulae around them, but most of the light comes from a point source.

2) Their spectra appear to be smooth (i.e. no strong absorption lines that a star might have) and flatter than a star. These 2 properties by themselves would make them a quasar.

3) Their visible light is often partially polarized.

4) Their output in all wavelength bands varies more rapidly and by a larger amount than a quasar.

Now, what is going on? As the website says, possibly a jet of material coming from near a black hole, with the gas in the jet moving very nearly the speed of light and coming nearly straight toward us.

I hope this helps,

Tim Kallman
for the Ask an Astrophysicist team

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