By Craig J. Hogan (auth.), D. Lynden-Bell, G. Gilmore (eds.)

The seen universe is a small perturbation at the fabric universe. Zwicky and Sinclair Smith within the Thirties gave proof of invisible mass within the Coma and Virgo Clusters of Galaxies. larger optical facts has in simple terms served to confound their critics and the X-ray info confirms that the gravitational potentials are time and again greater than these envisioned at the foundation of the saw stars. Dynamical analyses of person galaxies have discovered that major additional mass is required to give an explanation for their rotational velocities. On a lot higher scales, tens of megaparsecs, there's suggestive facts that there's much more mass according to unit luminosity. what's this non-luminous stuff of which the universe is made'? How a lot of it's there? want there be just one type of stuff? There are 3 uncomplicated possi bili ties:- it all is usual (baryonic) topic, it all is a few different form of (non-baryonic) topic, or a few of it truly is baryonic and a few is non-baryonic.

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Dark Matter in the Planetary System Dark matter located between the planets can be detected by its gravitational influence on planetary orbits. The best limits come from Kepler's law, which states that in the absence of dark matter the period P and semi-major axis a of a planet of negligible mass are related by (1) The perturbing effects of the planetary masses are straightforward to account for and will not be discussed here. Distances are measured in terms of the astronomical unit (AU), which is defined by the relation (2) The constant in the brackets is approximately 271" divided by the number of days in a year, so that the Earth's semi-major axis a$ is very nearly 1 AU.

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5H (see Figure 4). et brighter than Ho = 7 is insensitive to the assumed upper and lower limits of the mass distribution. 1 X 10 15 kg if the rough fit to the mass-magnitude relation shown in Figure 4 is adopted. With the latter normalization, the mass of the dynamically active Oort cloud is almost 60 M$, while the total mass of the model is nearly 500 M$! From the normalization adopted in Figure 4, these . 05/A)3/2(Pc/500kg m- 3 ), where A is the mean albedo for long-period comets. Such a high mass for the Oort cloud would, of course, virtually rule out a simple planetesimal hypothesis for cometary origin: the original mass of the Oort cloud could hardly have been less than twice its present value, while the initial cometary mass in the protoplanetary disc, allowing for the placement efficiency to the Oort cloud, must have been even larger - far greater, therefore, than the total mass of the observed planets.

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