The Problem of Missing Mass
Given our assumption that the universe is exactly flat, the missing mass problem is that there is not enough observable material so that in Newtonian cosmology the gravitational binding energy can exactly balance the kinetic energy, to give total energy zero, as required for a flat universe. Some physicists argue that in general relativity, the gravitational potential energy is just represented by the curvature term. But it is not clear that curvature can balance the much larger rest energy term E = mc2. The visible (luminous mass) accounts for only about 4-5 percent of the needed mass. Studying the rotation curves of galaxies and galaxy clusters reveals an invisible mass (called dark matter) contained inside the galaxies and clusters that amounts to perhaps 5-6 times the visible matter. Current cosmological theory accounts for the balance of missing mass by dark energy, also known as vacuum energy or the cosmological constant. An alternative source for the missing mass is that there may be more dark matter between the galaxies and clusters, in the intergalactic medium. This cannot be detected by rotation curve analysis. Matter distributed outside a sphere enclosing a galaxy cannot affect its interior motions. The intergalactic medium is assumed to be made of visible filamentary structures made of ionized hydrogen plasma surrounding large empty volumes called voids. If the voids contained dark matter, they would still appear to be empty. We find it plausible that the intergalactic medium contains about 3 times the density of visible and dark matter in galaxies and clusters. This amount of dark material can close the universe and explain its flatness. But it does not explain the apparent expansion acceleration seen in Type 1a supernovae. This may be an artifact of the assumption they are perfect "standard candles." Recent evidence suggests that the distant Type 1a supernovae are in a different population than those nearby.Normal | Teacher | Scholar
Calculating Missing Mass in the Intergalactic MediumGiven that there is invisible dark matter inside gravitationally bound galaxies and galaxy clusters, amounting to between 5 and 6 times the visible luminous matter, it seems clear there is some of the same dark matter in the intergalactic medium. There are a number of ways we can estimate the intergalactic dark matter.