Bureau Of Missing Masses

One of the most intriguing mysteries of astrophysics is the so-called "missing mass" problem: the mass of heavenly bodies as estimated on the basis of how much light they emit is vastly smaller than their mass as calculated through Newton's laws of gravity and motion.

A standard explanation for this conundrum is the supposed existence of invisible or "dark" matter that does not emit light or other radiation and therefore has so far escaped detection. Prof. Mordechai Milgrom of the Weizmann Institute's Condensed Matter Physics Department has proposed a radically different explanation.

According to Milgrom, the mystery disappears if we modify Newton's laws when dealing with gigantic galactic systems. In a study reported in the Astrophysical Journal (March 20, 1997, Vol. 478, No. 1), Milgrom provides new evidence for this theory, and applies it to the largest definable bodies of mass known to exist - galaxy superclusters having the form of long threads and referred to as large-scale filaments.

Milgrom maintains that Newtonian physics works fine for celestial bodies such as planets and stars, but not for more complex groupings of these bodies. For example, according to Newton's law of inertia, the force (F) required to produce any level of acceleration (a) of a body of mass (m) is equal to m times a , or F = ma . Milgrom claims that for very small accelerations - like those in complex heavenly configurations such as galaxies - force is proportional to the square of the acceleration and not to just the acceleration itself.

These and other proposed modifications of Newtonian physics would have a major impact on inquiries into the origin and composition of the universe.

In previous studies Milgrom's calculations were applied to galaxies (measuring tens of thousands of light years across), galaxy clusters (a few million light years in diameter) and galaxy superclusters (some 10 million light years in diameter). In the latest study, his calculations are extended to the large-scale filaments, which are tightly packed bunches of galaxy superclusters with a length of some 200 million light years each. If the mass of such bodies is determined in accordance with Milgrom's theory, referred to as MOdified Nonrelativistic Dynamics, then it is possible to account for all the matter estimated on the basis of the light they emit.

The Weizmann Institute of Science is a major center of scientific research and graduate study located in Rehovot, Israel