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Last month, a team of scientists led by Stacy McGaugh at Case Western Reserve University determined from observations of 153 galaxies that the dynamics of galaxy rotation seems to depend solely on the normal, visible matter in it (SN coverage here). It was a strong argument that rather than hypothesising dark matter to explain the oddities in galactic rotation, it may instead be necessary to modify the laws of gravity.
However, two scientists from McMaster University, Ben Keller and James Wadsley, have just recently examined the results of a detailed simulation of dark matter in galaxy formation previously done known as the McMaster Unbiased Galaxy Simulations 2 (MUGS2). The simulation was a sophisticated one that took into account various other factors such as gas dynamics, star formation, and stellar feedback, but incorporated no new physics beyond that of the standard Lambda-Cold Dark Matter (ΛCDM) cosmological model. They found that the relation that McGaugh et. al. discovered from observations of real galaxies was reproduced just about exactly by the simulation. Their paper is here. Their abstract states:
Recent analysis (McGaugh et al. 2016) of the SPARC galaxy sample found a surprisingly tight relation between the radial acceleration inferred from the rotation curves, and the acceleration due to the baryonic components of the disc. It has been suggested that this relation may be evidence for new physics, beyond ΛCDM. In this letter we show that the 18 galaxies from the MUGS2 match the SPARC acceleration relation. These cosmological simulations of star forming, rotationally supported discs were simulated with a WMAP3 ΛCDM cosmology, and match the SPARC acceleration relation with less scatter than the observational data. These results show that this acceleration law is a consequence of dissipative collapse of baryons, rather than being evidence for exotic dark-sector physics or new dynamical laws.
So now it seems that the earlier troubles with dark matter were actually the result of too naïve a simulation, and by taking into account additional known, relevant physics, the troubles disappear.
Further coverage and commentary by astrophysicist Ethan Siegel here (archive.is).
Related: Study Casts Doubt on Cosmic Acceleration and Dark Energy
(Score: 0, Flamebait) by andersjm on Saturday October 29 2016, @07:02AM
I'm going to to out on a limb here and say that the kind of pretentious mathematician who would even think to use a greek letter mixed into a latin lettered acronym, probably doesn't have good intuition about the nature of reality.
Based on that and that alone, I'm calling it: There is no such thing as dark matter.
You heard it here first, folks!
(Score: 2) by lgw on Saturday October 29 2016, @08:50AM
It's actually the name of the "standard model" of cosmology. Three theories stuck together with duct tape and bailing wire: big bang + CDM for dark matter + cosmological constant (lambda) for dark energy. Amusingly, it's Lambda-CDM - the big bang is silent.
The CDM part is reasonably uncontroversial at this point, though not yet settled obviously. The cosmological constant is entirely a guess, one of many dark energy theories, but it's the simplest so it's the starting point. The big bang part includes "inflation", but no particular inflationary model is standard, and there's a lot of work around whether inflation and dark energy are two unrelated effects, or one effect that evolved over time.
(Score: 3, Touché) by stormwyrm on Saturday October 29 2016, @09:45AM
Numquam ponenda est pluralitas sine necessitate.