Proof of dark matter papers – Problems in Big Bang Cosmology
1. Who’s right? Douglas Clowe’s
4. Andreas Albrecht, a cosmologist at the
Despite the provocative claims, “dark matter” particles (e.g. Wimps or axions) were not directly observed here on earth. Rather there was some weak circumstantial evidence which died not eliminate competitive explanations.
The following email explains some of the issues.
From: Eric Lerner [email@example.com]
Sent: Monday, August 28, 2006 10:42 PM
Subject: No proof of dark matter
I’m responding to many inquiries about the “proof of dark matter” papers, astro-ph0608407 and 0608408 by Clowe et al. and Bradac et al. Data in the second paper is needed to understand fully the first one.
The first paper is very inappropriately titled and does not at all prove what it claims--the existence of dark matter. The term “dark matter” is used in the scientific literature, and in this paper, as a synonym for non-baryonic matter, matter which is different from the ordinary matter observed anywhere on earth, including in particle accelerators. This paper does nothing to prove the existence of such matter.
What this paper actually provides evidence for is something very different: that in the case of this particular pair of colliding clusters of galaxies, the greater part of the mass is spatially associated with the galaxies and not with the hot intracluster gas. This evidence is that gravitational-lensing measures of total mass outline the concentrations of galaxies, which are physically separate from the main hot gas concentrations.
How do Clowe et al get from what was actually indicated to what they claimed? Only though a big assumption, which is in no way supported by their data.
The major assumption is that all of the baryonic, ordinary, matter is in the form of hot plasma or bright stars in galaxies. The paper shows that the total amount of gravitating matter, as measured by gravitational lensing, does not correlate with the amount of hot plasma, as measured by x-rays. Therefore, the authors argue, the gravitating matter is instead associated with the galaxies. Since the gravitating mass is much greater than the mass in easily-visible stars, and by assumption, there is no other baryonic matter, the mass must be non-baryonic or dark matter.
The flaw in this argument is this assumption that all the ordinary matter in galaxies is in easily-visible, bright, stars. Instead, most of the mass of galaxies may well be in the form of dwarf stars, which produce very little light per unit mass—in other words have a very high mass-to-light ratio. Several studies of galaxies using very long exposures have shown that they have ”red halos”, halos of stars that are mostly red dwarfs. Other studies have indicated that the halos may be filled with white dwarfs, the dead remains of burnt-out stars. In addition, there is evidence that a huge amount of mass may be tied up in relatively cool clouds of plasma that do not radiate much x-ray radiation, and would be in closer proximity to the galaxies than the hot plasma.
The Clowe paper in no way contradict these possibilities, so in no way prove the existence of dark, or non-baryonic matter. Instead, they assume that any mass associated with the galaxies that is not in bright stars is non-baryonic, dark matter. They assume what they seek to prove.
Clowe et al also argues that their results refute the idea that there could be a modified gravitational law such as MOND. Yet if the measurements of gravitating mass are accurate, the clusters are all in the non-MOND regime, where the gravitational acceleration is more than 10^-8 cm/sec^2, so the clusters don’t provide a test of MOND.
In short, this paper really adds almost nothing to the debate about dark matter. It was already well known that hot plasma and bright stars in galaxies do not contain most of the mass in most clusters.