By Robert H. Sanders
ISBN-10: 0511776152
ISBN-13: 9780511776151
ISBN-10: 0521113016
ISBN-13: 9780521113014
So much astronomers and physicists now think that the problem content material of the Universe is ruled through darkish topic: hypothetical debris which have interaction with basic topic basically throughout the strength of gravity. although invisible to present direct detection equipment, darkish topic can clarify various astronomical observations. This booklet describes how this concept has constructed during the last seventy five years, and why it's now a vital function of extragalactic astronomy and cosmology. present makes an attempt to without delay notice darkish topic in the community are mentioned, including the results for particle physics. the writer reviews at the sociology of those advancements, demonstrating how and why scientists paintings and engage. transformed Newtonian Dynamics (MOND), the best replacement to this concept, can be offered. This interesting evaluation will curiosity cosmologists, astronomers and particle physicists. arithmetic is stored to a minimal, so the ebook will be understood by way of non-specialists.
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Extra resources for The Dark Matter Problem: A Historical Perspective
Sample text
3. Because most of the emission is near the maximum (projected) rotation velocity, this produces the characteristic “double-horn” 21-cm line profile of spiral galaxies. Although we can estimate the rotation velocity from such a single-dish profile, the detailed rotation curve mapped using an interferometer is clearly preferable in determining the run of circular velocity with radius and, hence, the radial distribution of force (or mass with an assumed law of gravity). From Begeman (1989). a maximum velocity of 200 km/s but because of the 30-degree inclination the component of maximum rotation along the line-of-sight (the radial velocity) will be 100 km/s, approaching on one side and receding on the other.
Except for the closest galaxies, a single-dish telescope “sees” the entire galaxy in its beam, so the entire range of velocities is present within the 21-cm line. The resulting line profile (the shape of the line as a function of frequency or radial velocity) is similar to that shown in Fig. 4 – the characteristic “double-horn” profile. An interferometer has a higher spatial resolution and, for many galaxies, produces such a map of the entire two-dimensional velocity field. From Roberts (1975b).
The suggestion that visible galaxies are immersed in enormous dark halos has originated largely from theoretical considerations. Of course, there is a history of phenomenological hints in this direction – observations of “missing mass” in clusters of galaxies reported by Zwicky; an undetected contributor to the force perpendicular to the galactic plane reported by Oort; a need for extra mass in order to understand the approach of M31 to the Milky Way considered by Kahn and Woltjer. Moreover, as I discuss in the next chapter, observations of the extended rotation curves of spiral galaxies were just beginning to appear in the literature – observations which implied that the mass-to-light ratio was certainly increasing in the outer regions.
The Dark Matter Problem: A Historical Perspective by Robert H. Sanders
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