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The Question

(Submitted February 16, 1998)

Most known "naked" quasars have no nebulosity. This poses an obvious threat to some prominent theories about quasars. Do you have any ideas about the lack of host galaxies?

The Answer

Thank you very much for the question regarding quasars. It certainly is a puzzle: why in some cases, we do not see the nebulosities that we would expect to see surrounding quasars in the context of the current hypothesis of quasars being nuclei of galaxies. Most astronomers believe that those "naked quasars" are simply nuclei of relatively faint galaxies, and we simply haven't detected them with the most sensitive currently available instruments such as the cameras onboard of the Hubble Space Telescope. This is an area of intense study, and no consensus has been reached as yet. Needless to say, the discovery of an alternative answer would have an enormous payoff: abolishing the current theory of nature of quasars would lead to fame (but perhaps not fortune, as astronomers generally are not paid very high salaries...). Of course it is possible that the central region of the host galaxy formed stars first, and the more remote regions have much lower star formation rate... (the nebulosities we see are due to stars).

Greg Madejski and Damian Audley
for Ask an Astrophysicist.

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