Why do galaxies have emission spectrum and not absorption spectrum?
Stars have absorption spectra and an emission if you look at the gas cloud. But I don’t understand the galaxies.
It is only logical that both must exist.
{{{Direct quotation from source}}}
Thus, emission spectra are produced by thin gases in which the atoms do not experience many collisions (because of the low density). The emission lines correspond to photons of discrete energies that are emitted when excited atomic states in the gas make transitions back to lower-lying levels.
A continuum spectrum results when the gas pressures are higher. Generally, solids, liquids, or dense gases emit light at all wavelengths when heated.
An absorption spectrum occurs when light passes through a cold, dilute gas and atoms in the gas absorb at characteristic frequencies; since the re-emitted light is unlikely to be emitted in the same direction as the absorbed photon, this gives rise to dark lines (absence of light) in the spectrum.
You will also find images that help show this phenomena. t
Galaxies are putting out energy so they have emission spectra. Absorption Spectra is for things like gas clouds that are between us and the emitter
References :
Hi. Galaxies have both. Stars and ionized gas clouds are the emission source and cool gas and dust are the absorption features.
Edit. Dude is right, but both emission and absorption features can be located within a galaxy. Look at the Milky Way or the Sombrero Galaxy. http://www.google.com/search?ie=UTF-8&oe=UTF-8&sourceid=deskbar&q=Sombrero+Galaxy
References :
It is only logical that both must exist.
{{{Direct quotation from source}}}
Thus, emission spectra are produced by thin gases in which the atoms do not experience many collisions (because of the low density). The emission lines correspond to photons of discrete energies that are emitted when excited atomic states in the gas make transitions back to lower-lying levels.
A continuum spectrum results when the gas pressures are higher. Generally, solids, liquids, or dense gases emit light at all wavelengths when heated.
An absorption spectrum occurs when light passes through a cold, dilute gas and atoms in the gas absorb at characteristic frequencies; since the re-emitted light is unlikely to be emitted in the same direction as the absorbed photon, this gives rise to dark lines (absence of light) in the spectrum.
You will also find images that help show this phenomena. t
References :
http://csep10.phys.utk.edu/astr162/lect/light/absorption.html
Poet, Writer, Editor, Artist, Critic (freelance)