Dark Matter Mass: Evidence of Low-Mass?

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Discussion Overview

The discussion revolves around the mass of dark matter and whether there is evidence, particularly through gravitational lensing, that suggests it has a low mass compared to visible matter. The scope includes theoretical implications and observational evidence related to dark matter's properties.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants inquire whether the discussion pertains to the mass of dark matter particles or the total mass of dark matter in the universe.
  • It is noted that the total mass of dark matter is approximately five times that of normal matter.
  • Gravitational lensing is discussed as a potential indicator of dark matter mass, with micro-lensing ruling out certain mass ranges for massive objects like primordial black holes, but not for fundamental particle candidates.
  • One participant suggests the need for clarification regarding the comparison of masses, questioning the practical feasibility of comparing volumes of visible and dark matter.
  • Another participant states that in the galaxy, dark matter is more prevalent, while baryonic matter is more abundant on Earth.
  • The absence of low-angle scattering in microlensing is mentioned as evidence against the existence of dense lumps of dark matter, implying that dark matter may be distributed in larger, smoother densities.

Areas of Agreement / Disagreement

Participants express differing views on the implications of gravitational lensing for dark matter mass, and there is no consensus on whether dark matter is low-mass compared to visible matter. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

There are limitations regarding the definitions of mass being discussed, as well as the assumptions about the nature of dark matter and its distribution. The feasibility of comparing volumes of dark and visible matter is also questioned.

Ranku
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Is there any indication, such as through gravitational lensing, that dark matter has a low-mass compared to visible matter?
 
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Are you referring to the dark matter particle mass or the total mass of dark matter?

In the first case no, you have viable dark matter candidates in a very large span of masses. In the second, the total mass of dark matter in the Universe is about five times that of normal matter.
 
Orodruin said:
Are you referring to the dark matter particle mass or the total mass of dark matter?
I meant in the first case. Does gravitational lensing indicate anything, one way or another?
 
Ranku said:
I meant in the first case. Does gravitational lensing indicate anything, one way or another?
Micro-lensing rules out some range of masses for quite massive objects such as primordial black holes. When it comes to fundamental particle candidates, it does not.
 
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Ranku said:
Is there any indication, such as through gravitational lensing, that dark matter has a low-mass compared to visible matter?

I think you need to clarify this question. How much are we talking about? A kilogram of each weighs the same, no?
 
Vanadium 50 said:
I think you need to clarify this question. How much are we talking about? A kilogram of each weighs the same, no?
I mean in terms of comparable volumes of visible and dark matter - although not sure how practically feasible it is to compare between volumes.
 
In the galaxy as a whole, there is more dark matter. In the earth, there is more baryonic matter.
 
If there were dense lumps of dark matter then microlensing of light by such dense lumps of dark matter would show up as low angle scattering.
Absence of such low angle scattering suggests lack of lumps of certain sizes, and that dark matter is divided into big but low and smooth density lumps.
 
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