Necessity of Dark Matter in Modified Newtonian Dynamics within Galactic Scales

It has long been known that Newtonian dynamics applied to the visible matter in galaxies and clusters does not correctly describe the dynamics of those systems. While this is generally taken as evidence for dark matter it is in principle possible that instead Newtonian dynamics (and with it General Relativity) breaks down in these systems. Indeed there have been a number of proposals as to how standard gravitational dynamics might be modified so as to correctly explain galactic dynamics without dark matter. I will review this general idea (but focus on “MOdified Newtonian Dynamics”, or “MOND”), and discuss a number of ways alternatives to dark matter can be tested and, in many cases, ruled out.

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The Modified Newtonian Dynamics as an Alternative to Hidden Matter

Symposium - International Astronomical Union ◽

10.1017/s0074180900150442 ◽

1987 ◽

Vol 117 ◽

pp. 319-333

Author(s):

Mordehai Milgrom ◽

Jacob Bekenstein

Keyword(s):

Dark Matter ◽

Main Body ◽

Modified Newtonian Dynamics ◽

Newtonian Dynamics ◽

Nonrelativistic Theory ◽

The Masses ◽

Modified Dynamics

The mass discrepancy, which has led to the notion of dark matter may, in fact, be due to a breakdown of the Newtonian laws which are used to determine the masses of galactic systems. We describe a nonrelativistic theory which departs from Newton's in the limit of small accelerations. When one uses the modified dynamics to deduce gravitational masses, the need to invoke large quantities of dark matter disappears. We outline the theory and give criteria for deciding which systems are expected to exhibit marked departures from Newtonian behaviour. The main body of the talk is a succinct description of the major predictions of the theory regarding dynamics within galaxies.

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An alternative to dark matter: modified Newtonian dynamics

The Dark Matter Problem ◽

10.1017/cbo9781139192309.010 ◽

2014 ◽

pp. 132-149

Author(s):

Robert H. Sanders

Keyword(s):

Dark Matter ◽

Modified Newtonian Dynamics ◽

Newtonian Dynamics

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The total mass of the early-type galaxy NGC 4649 (M60)

Serbian Astronomical Journal ◽

10.2298/saj0877001s ◽

2008 ◽

pp. 1-7

Author(s):

S. Samurovic ◽

M.M. Cirkovic

Keyword(s):

Dark Matter ◽

Total Mass ◽

Globular Clusters ◽

X Rays ◽

Early Type ◽

X Ray ◽

Modified Newtonian Dynamics ◽

Newtonian Dynamics ◽

Early Type Galaxy

In this paper the problem of the total mass and the total mass-to-light ratio of the early-type galaxy NGC 4649 (M60) is analyzed. Use is made of two independent techniques: the X-ray methodology which is based on the temperature of the X-ray halo of NGC 4649 and the tracer mass estimator (TME) which uses globular clusters (GCs) observed in this galaxy. The mass is calculated in Newtonian and Modified Newtonian Dynamics (MOND) approaches and it is found that inside 3 effective radii (Re ) there is no need for large amounts of dark matter. Beyond 3Re the dark matter starts to play important dynamical role. The possible reasons for the discrepancy between the estimates of the total mass based on X-rays and TME in the outer regions of NGC 4649 are also discussed.

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