Spectroscopy of Stars: Electrons in Plasma

[Sophrosyne]

Astronomers can determine the presence various elements in a star through spectroscopy of the incoming light from that star. The characteristic spectral lines of each element are formed by electrons transitioning between the various orbital energy levels around the nucleus of their atom.

But stars are in a plasma state. The electrons and nuclei are moving around too fast for stable electron orbits to develop. So how can you do spectroscopy on a star if you don't have electrons in orbits around nuclei?

 

[Bandersnatch]

Stars are not all plasma. The outer layers of stars are cool enough for the plasma to recombine into atoms. Spectroscopy tells you about the composition of those upper layers only.

 

[Chronos]

A star produces two kinds of spectral lines, emission and absorption. See https://imagine.gsfc.nasa.gov/science/toolbox/spectra1.html for further discussion.

 

[Sophrosyne]

Stars are not all plasma. The outer layers of stars are cool enough for the plasma to recombine into atoms. Spectroscopy tells you about the composition of those upper layers only.

This makes sense. Thanks.

 

[Ken G]

What's more, you can get spectral lines even if the electrons are only bound to the nuclei for very short times. Even a highly ionized gas will always have a tiny fraction of its atoms in a state that can absorb light for a short time. Also, many types of nuclei have a large positive charge, so it is very difficult to strip all their electrons, even if the hydrogen are largely stripped.