Dark matter solution: not receiving all the light?

Hypothetically, if we weren't receiving all the light from a galaxy, is it possible that this would reconcile the gravitational shortfall we perceive?

Would it not also explain the gravitational lenses that we attribute to dark matter (since we are not receiving all the light to represent the appropriate amount of matter that causes the lens)?

Let me know if I'm not being clear enough I will try to elaborate. I look forward to your input.

But isn't light the only 'tool' that astronomers have to study objects outside our solar system? If we weren't getting all the light then our calculations would be off no?

EDIT:

If we weren't getting all the light from the galaxy, then our calculations of how much mass is present would be less. If this is less, then so would our calculations of the gravity required to hold to galaxy together.

The rotational speed of the outer solar systems in the galaxy is utterly independent of how many photons reach Earth and it is that rotational speed that leads to conclusions about total mass.

I thought that the problem was missing mass, ie dark matter. Is this not correct?

And I thought that astronomers determined the mass by the luminosity of the galaxy. Perhaps this is where I err?

In addition to the numerical discrepancy between the Orbital and Brightness methods, the overall pattern of the orbital speeds of the stars within galaxies (constant orbital speed with increasing distance) is fundamentally different from the expected pattern (orbital speed declining with increasing distance). Thus, even if the actual masses of stars in distant galaxies were higher than current estimates, this would only have the effect of moving the plot for expected orbital speed in Figure 6 (chapter 1) upwards. It would not alter the plot's overall pattern so that it matched the observed plot. Thus, the stars and gas alone cannot explain the observed speeds of stars, no matter how large their combined mass is.

Hypothetically, if we weren't receiving all the light from a galaxy, is it possible that this would reconcile the gravitational shortfall we perceive?

Would it not also explain the gravitational lenses that we attribute to dark matter (since we are not receiving all the light to represent the appropriate amount of matter that causes the lens)?

Let me know if I'm not being clear enough I will try to elaborate. I look forward to your input.

From https://www.perimeterinstitute.ca/Pe...htness_Method:

I don't understand this statement. Wouldn't adding dark matter to the equation (in the stead of apparently absent luminous matter) have the same effect of pushing the expected orbital speed upwards as well? Or is it the way that the dark matter is supposedly distributed differ from that which the absent luminous matter would be distributed. If so -- ie if dark matter is distributed differently -- what is this unique pattern and how does it vary with r?

Thank you in advance for your careful consideration and explanation.

Hypothetically, if we weren't receiving all the light from a galaxy, is it possible that this would reconcile the gravitational shortfall we perceive?