For many years, astrophysicists and cosmologists have been searching for “Dark Matter”, an elusive source of matter needed to explain orbital velocities in stars, galaxies and galactic clusters.
At present, “Dark Matter” is only a theoretical concept. Attempts to locate it experimentally have so far been unfruitful. Theoretical suggestions for its location have included that it exists as “WIMPS” (Weakly Interactive Massive particles) that interact only through gravity and the weak force — not through electromagnetic radiation.
But now the likely nature of Dark Matter has emerged unexpectedly through an analysis of how solar systems form. Australian researcher David Noel had assembled evidence on the orbits of planets, planetoids, comets, and dwarf planets in our solar system.
He noticed that all the true planets, out as far as Neptune, some 30 AU from the Sun, orbited in a rough plane — the plane of the ecliptic. Maximum inclination of planetary orbits is only about 7 degrees. But beyond Neptune, orbits of objects became more and more inclined to the ecliptic.
Objects closer to the Sun orbit closer to the ecliptic.
By the time the Oort Cloud is reached, orbits are essentially random.
Immediately beyond Neptune and out to about 50 AU lies the inner Kuiper Belt, home of dwarf planets Pluto (orbit inclined at 17 degrees to the ecliptic) and Makemake (29 degrees). Out further, from 50 to 100 AU from the Sun, lies the Outer Kuiper Belt or Scattered Disc, including the most massive known dwarf planet, Eris, with an orbit inclined at 44 degrees to the ecliptic.
Beyond about 100 AU lies the Oort Cloud, source of long-period comets. Orbits of these comets are random with respect to the ecliptic. The conclusion drawn from the analysis is that the Sun’s gravitational influence essentially ends at the edge of a sphere 100 AU in radius.
Inside this sphere, the Sun has flattened the orbits of objects to conform with the ecliptic, closer objects very much so, more distant ones to a lesser extent. The analysis concludes that our solar system formed by reworking existing matter within this 100 AU radius sphere.
The unexpected identification of Dark Matter was a logical consequence of assuming that the Oort Cloud out beyond 100 AU has a similar mass per unit volume as the solar system. In the model, called the Cosmic Smog Model, planets and stars are assumed to have formed from a galaxy-wide fog of dust and gases.
Within the Smog, matter will aggregate into planetesimals of every size. A solar system is formed when aggregation in a given volume has taken place such that one of the planetesimals has built up to stellar mass. The new star then slowly clears and regularizes the area within its gravitational influence, leaving some larger planetesimals as orbiting planets.
The Oort Cloud can be treated as a sphere extending out to 100,000 AU, almost half-way to the nearest star. With a radius 1000 times that of the Solar System, its volume is a billion times greater. If the Solar System is the result of a local aggregation of a part of the Oort Cloud, then the mass of the Oort Cloud sphere must be a billion times that of the Solar System.
This previously-unidentified mass is the obvious candidate for Dark Matter. It then consists of ordinary-matter planetesimals lying between the stars, reacting normally with gravity and light, but distant enough to lie beyond the resolution of today’s telescopes, and not massive enough to reach the stellar limit at which it would shine by its own light.
The source article is at: The Cosmic Smog model for solar system formation, and the nature of ‘Dark Matter’.