Is Dark Matter Going Out of Style?
Dark matter has been a staple in cosmological theories for decades. One of the initial reasons was that galaxy rotation curves could not be explained without it. Another was that galaxy clusters, to be held together over long ages, needed more “stuff” to bind them. Finally, Big Bang cosmologists invoke copious amounts of dark matter and (more recently) dark energy to make their models work. What the dark matter is has remained an unanswered question. If it were normal “baryonic” matter we would see it, and it would not be “dark” (i.e., undetectable by current methods).
On the scale of galaxies, a paper in the Astrophysical Journal has undermined some of the justification for dark matter. Brownstein and Moffat found a way to account for galaxy rotation curves without it1 (see also summary on EurekAlert).
On the cosmological scale, two other papers show that dark matter and dark energy are not simple parameters to model. An American-Israeli team writing in Astrophysical Journal2 put constraints on cosmological simulations of dark matter halos and showed the picture is complex: “the clear separation of the evolution of an individual halo into series of quiescent and violent phases explains the inability to fit its entire evolution by simple scaling relations, in agreement with previous studies,” they wrote. A news story in Science3 described some of the ruckus over dark energy’s role in the cosmos. Specifically, astronomers are arguing about using gamma-ray bursts as a “standard candle” to infer the history of dark energy in cosmological theories. See also the reprint on EurekAlert of a report from New Scientist that said, “the result stressed how little we know about dark energy and the need for different approaches.”
1J. R. Brownstein and J. W. Moffat, “Galaxy Rotation Curves without Nonbaryonic Dark Matter,” Astrophysical Journal 636:721-741, 2006 January 10, 2006.
2Romano-Diaz et al., “Constrained Cosmological Simulations of Dark Matter Halos,” Astrophysical Journal 637:L000, 2006 February 1, 2006.
3Robert Irion, “Astronomers Push and Pull Over Dark Energy’s Role in Cosmos,” Science 20 January 2006: Vol. 311. no. 5759, p. 316, DOI: 10.1126/science.311.5759.316.
In the history of science, practitioners sometimes invoked “imponderable substances” in their theories. These included phlogiston, caloric, wound salve, ether, electricity, magnetism, and animal magnetism. Some of these substances went the way of the dodo, others became staples of science. So far, it appears that cosmologists are in the dark about dark matter (put “dark matter” in the search box above and see). It will be interesting to see how future astronomers look back on this period. Till established, theories built on dark matter should be treated like phlogiston theory or The Force. Duct tape is like The Force. It has a dark side, a light side, and it holds the universe together – at least as well as dark matter.