Andromeda M31 Spectrum
When calculating the velocity of M31 relative to Earth NASA uses the shift in two absorption lines for Calcium.
Is that really telling us the motion of the entire galaxy?
An absorption line results from a particular element or compound absorbing that specific wavelength because an electron can move to a higher energy state.
An emission line occurs when an electron drops to a lower energy state and that energy is released in the specific wavelength for that state change.
When we view the light from M31 it is the summation of the electromagnetic radiation from all 1 trillion (or so) stars in our view. I expect in that mix any variations in emission lines and absorption lines probably get washed out.
Somewhere betwen the stars in M31 and us on Earth there is Calcium absorbing its two wavelengths.
There are two possibilities:
1) it is possible that all the stars in M31 have the Calcium in their atmosphere and the summation never finds a star with no calcium, to fill in that wavelength.
2) the calcium is closer to Earth than M31 so the light from all the stars passes through it.
The 2nd seems much more likely than the first. The fact blue shift objects are usually close to Earth also indicates this conclusion. That also means with analysis of many spectra the calcium cloud could be delineated.
I cannot find online whether all the blue shift objects are using the same Calcium absorption lines as M31. M33 distance is similar to that to M31; they also have similar blue shifts; but their declination is different by about 11 degrees. I find no spectrum data for it.
Regardless, any absorption lines are not necessarily absorbed only by elements in the star's atmosphere.
I posted about this blue shift in the nearby galaxies on 04/04.
If we are using the motion of Calcium atoms in the space within our local group to calculate the motions of objects behind the calcium then this is clearly a mistake.
On 4/6 I posted about quasars being measured by hydrogen emission lines, allowing superluminal velocities.
On 4/10 I posted about the possibility intergalactic hydrogen might cause a red shift.
Cosmology absolutely relies on its assumption a shift of a line in a spectrum is always the velocity of that large object.
If that critical assumption is shown to be invalid in many cases the consequences are catastrophic.
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