Time to overhaul Newton's theory of gravitation? Galaxy cluster models cast doubt on dark matter
For almost 75 years, astronomers have believed that the Universe has a
large amount of unseen or ‘dark’ matter, thought to make up about
five-sixths of the matter in the cosmos. With the conventional theory
of gravitation, based on Newton’s ideas and refined by Einstein 92
years ago, dark matter helps to explain the motion of galaxies, and
clusters of galaxies, on the largest scales.
Now two Canadian researchers
at the Perimeter Institute for Theoretical Physics suggest that the
motion of galaxies in a distant cluster is more easily explained by a
Modified Gravity (MOG) theory than by the presence of dark matter.
Graduate student Joel Brownstein and his supervisor Professor John
Moffat of the University of Waterloo present their results in a paper
in the 21 November edition of Monthly Notices of the Royal Astronomical Society.
The two scientists analysed images of the ‘Bullet Cluster’ of galaxies made using the Hubble Space Telescope,
Chandra X-ray and Spitzer infrared observatories and the Magellan
telescope in Chile. The Bullet Cluster consists of two merging clusters
of galaxies and lies at a distance of over 3 billion light years in the
direction of the southern constellation of Carina.
This arsenal of instrumentation gave them maps of the 150 million
degree hot gas between the galaxies and show the effect of
gravitational lensing, where the gravity of an intervening object –
here the Bullet Cluster - deflects the path of light emitted by a more
distant galaxy.
Previous studies suggested that the Bullet Cluster clearly
demonstrates the presence of dark matter. But when Brownstein and
Moffat compared the observed gravitational lensing and distribution of
gas with that predicted using MOG theory, they found no evidence for
this. In other words, it is more natural to explain the appearance of
this cluster using a revised theory of gravitation than by including
dark matter.
MOG theory emerges from a
generalization of relativity that eluded even Einstein, has been
developed by Moffat for nearly thirty years and is now yielding
astronomical and cosmological results. The theory has been used to
successfully explain the movement of stars in over 100 galaxies and the
motion of galaxies in more than 100 clusters. MOG theory may also
explain the apparent anomalous deceleration of the Pioneer 10 and 11
space probes, launched in the early 1970s and now more than 12000
million km from the Sun.
The two physicists are
enthusiastic about their findings. Brownstein comments, ‘Using Modified
Gravity (MOG) theory, the ‘normal’ matter in the Bullet Cluster is
enough to account for the observed gravitational lensing effect. In
time, better observations will lead to higher resolution pictures of
the systems we are studying. Continuing the search for and then
analysing other merging clusters of galaxies will help us decide
whether dark matter or MOG theory offers the best explanation for the
large scale structure of the Universe.’
Professor Moffat adds, ‘If the multi-billion dollar laboratory
experiments now underway succeed in directly detecting dark matter,
then I will be happy to see Einsteinian and Newtonian gravity retained.
However, if dark matter is not detected and we have to conclude that it
does not exist, then Einstein and Newtonian gravity must be modified to
fit the extensive amount of astronomical and cosmological data, such as
the bullet cluster, that cannot otherwise be explained.’
Source: Royal Astronomical Society
Via: http://www.physorg.com/news113031879.html
