Can I see a quasar? (Intermediate)

Can you find quasars with an ordinary telescope from earth? If they are so bright why or why not?

With a mid-sized telescope, you can probably see a quasar. Here is a list of the brightest quasars; as you can see, the brightest is about 13th magnitude (variable).

If you do manage to see one, don't be disappointed if it looks just like a star--keep in mind what an amazing object you are looking at!

By far the most popular theory (see (**) below for other theories) concerning the nature of quasars says that they lie in extremely distant galaxies, so that the high redshifts measured in their spectra are due to the expansion of the universe (redshifts are measured as high as 5.5, corresponding to a distance of about 14 billion lightyears). In this case, to account for even the relatively modest observed brightnesses, the quasars must emit enormous amounts of radiation (even considering gravitational lensing)--thus quasars are extremely luminous (bright if you are standing next to them), but not extremely bright due to high distance. Possible sources for this extraordinary amount of radiation include gas flowing into a very massive black hole, galactic interaction, stimulating intense stellar formation, and a very massive, magnetic spinning object of some sort. Of course there are many other possibilities, but we must bear in mind that the source must somehow be unique to the young universe, since we don't see any nearby (full-grown) quasars and that many quasars vary in dramatically in brightness over days or weeks, which puts a limit on the size of the source.

(**)(The theory outlined above has been strongly supported by the resolution of many host galaxies. Another theory interprets quasars as objects whose redshifts are due to expulsion from local galaxies. Yet another says that the redshifts are not due to velocity at all, but to laser action in the rapidly-expanding atmosphere of a star in our own galaxy. And then there's the theory that says they are interstellar starships, and we only see the ones headed away from us due to relativistic narrowing of the beam angle--needless to say, there are multiple problems with this one...)

This page was last updated June 27, 2015.

About the Author

Sara Slater

Sara is a former Cornell undergraduate and now a physics graduate student at Harvard University, where she works on cosmology and particle physics.

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