Dark matter

Dark matter, in astronomy, is any hypothetical matter that is not directly detectable but which astronomers infer when the actual mass of any observed celestial object is not sufficient to account for an observed gravitational effect. It is one of two concepts (the other is dark energy) that conventional astronomers invoke to account for observations that conventional cosmologies, including the Big Bang, cannot explain.

The first dark matter

Main Article: Vulcan

The first recorded instance of the invocation of anything similar to dark matter was the hypothesis of a planet named Vulcan. This planet was supposed to be inside the orbit of Mercury and yet was never observed from Earth, for reasons that no astronomer ever explained. Astronomers inferred the existence of this planet because Mercury precessed in its orbit around the Sun by 43 arc-seconds per century faster than its own mass, and that of the sun, would predict.

Then in 1915, Albert Einstein solved the problem. He showed that Mercury, at perihelion, passes close enough to the Sun for General Relativity to require a second-order correction. He published the correction and accounted exactly for the precession in the orbit of Mercury, without the need for any planet, asteroid belt, or other object or objects inside that orbit.

In solving the orbit of Mercury, Albert Einstein followed Occam's Razor. Future cosmologists would not heed his advice.

Modern conventional concept

The present concept of dark matter dates from the 1930's, when astronomers first found serious differences between the masses they inferred by examining orbital speeds and the masses they inferred by measuring stellar, galactic, and other visual magnitudes.

The mathematical problem

This classic equation, derived from the theory of gravity of Sir Isaac Newton, gives the total dynamical mass in any system that is inside the orbit of any given body (for example, a particular star in its galaxy):

where R is the distance of the body from the barycenter, v is the orbital speed of that body, and G is the gravitational constant.

The luminous mass of any galaxy or other object is the mass that corresponds to the measured light from the object.

Jan Oort first determined that the total mass of our galaxy was insufficient by a factor of at least two to account for the galaxy's rotational speed. The swiss astronomer Fritz Zwicky is also credited with the discovery of the discrepancy between dynamical and luminous mass, in 1933. Zwicky examined the Coma supercluster, and found that its dynamical mass exceeded the luminous mass by a factor of ten.

Image of galactic cluster with ring of alleged dark matter around it

Since that time, astronomers have assumed that some form of matter, which gives off no measurable radiation, is nevertheless present in various galaxies and galactic clusters that clearly spin faster than their measured luminous masses would predict. They acknowledge, however, that the notion of a new, non-luminous form of matter is difficult to accept. Yet many astronomers insist that they have observational evidence for which dark matter remains the only plausible explanation. One such communication comes from the Chandra X-ray Center, whose astronomers stated in 2006 that they had observed two galactic clusters for hundreds of hours, and that each one clearly showed a rotational speed consistent with far more mass than was visible.

Estimated proportion

The Wilkinson Microwave Anisotropy Probe (WMAP) team at NASA has used measurements of cosmic microwave background radiation to determine that the universe is geometrically flat. According to standard cosmology, the universe should then be at a critical mass density of 9.9 * 10^-27kg/m³. The actual mass density of the universe is more than twenty times less than that.

Current theory suggests that the familiar baryonic matter (composed of atoms) constitutes only 4.6% of the total mass-energy in the universe. Dark matter constitutes 23% of the total, while dark energy comprises the remaining 72%.

Candidates for dark matter

Conventional astronomers have generally focused on the following explanations for the discrepancy between dynamical and luminous mass:

1. Brown dwarf stars and similarly massive but relatively non-luminous objects. Astronomers have in fact invented a new name for a class of objects that include brown dwarf stars and other massive objects: Massive Compact Halo Objects, or MACHOs.
2. Supermassive black holes. Astronomers are now attempting to detect these objects by their relativistic effects on light, in which they act as lenses.
3. New, previously unknown forms of matter. Many cosmologists have formed hypotheses that suggest entirely new particles of matter. They call these Weakly Interactive Massive Particle, or WIMPs. Other cosmologists have suggested other types of particles, named axions. The recently sought Higgs boson is another candidate for a dark-matter elementary particle.
4. A new theory of gravity. In 1983, Mordecai Milgrom first suggested that Newtonian dynamics was insufficient to explain the gravitational interactions of massive objects like galaxies and galactic clusters. He therefore suggested a Modified Newtonian Dynamic, or MOND, in which gravitational attraction varied inversely to the first power of the orbital radius, not its square as Newton originally assumed.

Tim Thompson has recently suggested yet another possibility to which most conventional astronomers pay scant attention. He suggests that the major attractive force that allows galaxies and systems of higher mass to rotate with such excessive speed is not gravity at all, but electrostatic forces. He reminds his readers that electrostatic forces are stronger than gravity, and also that the strength of a magnetic field varies inversely as the first power, not the square, of the distance from the center. This is very close to Milgrom's MOND, with the advantage of having an underlying theory to explain it, which Milgrom's system does not have.

Creationist perspectives

In 2000, Don DeYoung, writing in the Creation Research Society Quarterly, challenged the notion of dark matter as a fanciful concept with little justification. He pointed out that none of the conventional explanations popular at the time were satisfactory:

1. Non-luminous stars, the usual candidates for MACHOs, would have to be far more common than they actually are, by several orders of magnitude, for them to account for the mass deficit.
2. Black holes are a theoretical construct that have not thus far been verified.
3. Efforts to detect WIMPs and axions have thus far produced no definitive findings.

DeYoung also challenged the notion that galaxies or galactic clusters were necessarily stable. He did not comment directly on Milgrom's modified dynamic, but he did suggest that gravity was poorly understood.

DeYoung then concluded that the hand of God was responsible for holding rapidly spinning galaxies and larger systems together, despite the observed mass deficits. But John Hartnett has recently produced a solution that requires no continuing miracle, but derives from a new understanding of the creation and expansion of the heavens. Hartnett's system builds on the earlier work of Carmeli, who in 1996 proposed an extension of Einsteinian relativity to the cosmic scale (Cosmological Relativity). The Hartnett system, explained more fully in his work Starlight, Time and the New Physics, predicts that an expanding universe will produce rapidly spinning galaxies and larger systems as a consequence of the expansion and not due to gravity (or any other force) alone.