Absorption lines and emission lines in stellar spectra

In summary, the reason why we see more absorption lines in stellar spectra than emission lines is that most stars have a cooler surface than their interior, causing the light to be absorbed by colder gas as it passes through the upper layers of the atmosphere. The emitted lines become bands that are not easily identifiable, while the cooler, lower pressure gas surrounding the star only absorbs narrow band ranges. Emission lines are only likely to be found in low density gases subjected to high levels of energy from nearby stars, resulting in lower power compared to the absorbed power by gases surrounding a star. This is why emission lines are visible against the dark background of deep space.
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Haynes Kwon
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Why do we see more absorption lines in stellar spectra than emission lines?
Why do we see more absorption lines in stellar spectra than emission lines?
 
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The surface of the sun is cooler than the interior.
 
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Likes Orodruin
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Emission lines are present in spectrum of only few types of stars, see
https://en.m.wikipedia.org/wiki/Emission-line_star

Most of the stars exhibits only absorption lines (superimposed on the continuous blackbody radiation). As the light radiated in photosphere propagates through upper layers of stellar atmosphere, some of the wavelengths are absorbed by colder gas.
 
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Haynes Kwon said:
Why do we see more absorption lines in stellar spectra than emission lines?
The light from the very hot interior or near the surface will have a continuous spectrum. The material is very dense and the atoms / ions will be moving very fast. Those factors cause the emitted lines to become bands, which are not easy to identify.
Otoh, the cooler, lower pressure gas which surrounds a star will absorb only narrow band ranges (lines) of the spectrum.
I think you would only be likely to find emission lines from low density gases (say, on nebulae) that are subjected to high enough levels of high energy particles and photons from 'nearby' stars. They can produce line emission spectra as they are under more like 'lab' conditions.
The power of emission lines will be low, too, because of the circumstances (very distant from their energy source) - much lower than the absorbed power by gases which surround a star. They will be visible against the Dark background of deep space.
I think that makes some logical sense.
PS Those conditions can happen where the star is of the kind described in the above link where there is a high level of UV energy from a very hot star and that causes excitation of the nearby gases to emit optical energy photons against a relatively low optical background from the star itself.
 

1. What are absorption lines and emission lines in stellar spectra?

Absorption lines and emission lines are features observed in the spectra of stars, which are produced by the interaction of light with the atoms and molecules in the star's atmosphere. Absorption lines are dark lines in the spectrum, indicating that certain wavelengths of light have been absorbed by the atoms in the star's atmosphere. Emission lines, on the other hand, are bright lines in the spectrum, indicating that certain wavelengths of light have been emitted by the atoms in the star's atmosphere.

2. How are absorption lines and emission lines used in studying stars?

Absorption lines and emission lines are used to study the chemical composition, temperature, and motion of stars. By analyzing the wavelengths and intensities of these lines, scientists can determine which elements are present in the star's atmosphere, as well as their abundance. The width and shape of the lines can also provide information about the temperature and motion of the star.

3. What causes absorption lines and emission lines in stellar spectra?

The absorption and emission lines in stellar spectra are caused by the absorption and emission of light by the atoms and molecules in the star's atmosphere. When light passes through the atmosphere, certain wavelengths are absorbed by the atoms, causing dark lines to appear in the spectrum. Other wavelengths are emitted by the atoms, resulting in bright lines in the spectrum.

4. How do absorption lines and emission lines differ from each other?

The main difference between absorption lines and emission lines is the direction of the light. Absorption lines occur when light is absorbed by the atoms in the star's atmosphere, while emission lines occur when light is emitted by the atoms. Additionally, absorption lines appear as dark lines in the spectrum, while emission lines appear as bright lines.

5. Can absorption lines and emission lines be used to identify different types of stars?

Yes, absorption lines and emission lines can be used to identify different types of stars. Each element in a star's atmosphere produces a unique set of absorption and emission lines, allowing scientists to determine the chemical composition of the star. Additionally, the presence or absence of certain lines can indicate the temperature and motion of the star, providing further information about its type and characteristics.

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