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Why do quasars have a emission spectra?

If quasars are emitting light should they not have an absorption spectra?

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  • 2 months ago

    Quasars do have absorption lines I'm their spectra. 

    http://www.tapir.caltech.edu/~sperhake/Research/Qu...  

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  • cosmo
    Lv 7
    2 months ago

    If you have a gas at some temperature with multiple elements in it, surrounded by other gas at some other temperature, also with multiple elements, the "radiative transfer" at each particular wavelength is complex.  Lots of electronic transitions are happening, upwards and downwards in the energy ladder of the various atoms and ions and free electrons as a result of magnetic field effects, collisions, spontaneous radiative transitions, and induced radiative transitions.  It is, in fact, even possible to have "LASER" or "MASER" effects, leading to super-thermally bright line emission.

    So, I'm afraid the answer is: it's complicated.  The result of many effects must be considered at each frequency (and that's complicated by the fact that bits of the gas are moving at different velocities and so there are always Doppler shifts).  In quasars, the "nebular lines" which tend to have long timescales for spontaneous emission can be heavily excited and become more optically thick, while the continuum processes of the free electrons are more optically thin, resulting in an emission line that is not absorbed when the line-of-sight does not subsequently pass through a denser, dusty region.  That's just the way it is, the cumulative effect of the parameters of many state transitions.

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  • 2 months ago

    Because the Centre of them are made up of Supermassive Black Holes

    They are the precursors of Galaxies

     Remember how far away thus how far back in time that they are

    Attachment image
    Source(s): A Quazar Yesterday, refused to comment
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  • 2 months ago

    I don't understand the question - if they're emitting light you'd expect an emission spectrum!  But they also produce absorption spectra - mostly from intervening gasses but some produce "intrinsic" absorption lines, caused by local gas.

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