# Can someone explain how to determine density using absorbption spectrum? (1 Viewer)

#### SB257426

##### Very Important User
So basically I was watching a vid and this dude said when there is high density there is more collisions (which i understand why) but he also said they change the energy of the electrons' orbitals which I dont get how that relates to density........

This is my explanation to it but im unsure if it is correct or not:

As EMR interacts with a star with lower density there will be less collisions with particles so the electrons will not be able to absorb as much light so stars with lower density have finer spectral lines. But when EMR reacts with stars that have high density the number of collisions will increase significantly thus the amount of light that the electrons can absorb will be more so we will see broader spectral lines for the element that is absorbing light.

#### wizzkids

##### Active Member
It sounds like you are doing Module 7 The Nature of Light and you are up to the dot point about :
"Investigate how the spectra of stars can provide information on:
- surface temperature
- rotational and translational velocity
- density
- chemical composition"

The syllabus does not require students to explain the mechanism of spectral line broadening due to density (gas pressure). All you are required to know is that spectral line broadening is an indicator of gas pressure. Broader lines indicate higher pressure, and narrow lines are an indication of lower pressure. High pressure is found in white dwarf stars and low pressure is found in large inflated stars like red giants.
Mechanism
If spectral lines are broader, it means that the outer electron energy levels must be less well defined. The effect is not due to any variation in the amount of light that the ionised electron absorbs. Each electron always absorbs one quantum of energy. It is the difference between the initial potential energy and final potential energy of the electron that determines the quantum of energy that is emitted or absorbed when electron recapture occurs. Gas pressure subtly alters the electron wave function of these outer electrons. They become a bit more random as pressure increases. Hence the energies of the emitted quanta are spread across a wider range.

Last edited: