New test may provide 'smoking gun' for modified gravity

New test may provide 'smoking gun' for modified gravity: Now in a new paper published in Physical Review Letters, Wojciech A. Hellwing, et al., have proposed a new test of modified gravity that is based on measuring the tendency of well-separated galaxies to approach each other. This movement is called the galaxy pairwise velocity.
The physicists show that the galaxy pairwise velocity distribution of many galaxies with a wide range of masses is expected to deviate from the predictions of general relativity by significant amounts: between 5 and 10 standard deviations or higher, depending on the model. Due to these large deviations, this proposed test could potentially offer the strongest evidence in support of modified gravity to date.

Nearby dark-matter-free zone poses cosmic conundrum

Nearby dark-matter-free zone poses cosmic conundrum: ...until now most velocity measurements considered only stars zipping around the Milky Way radially, like an ant sitting on a vinyl record. By contrast, Moni Bidin's team looked outward from the plane of the galaxy, perpendicular to the galactic disc. Using historical survey data and new observations from telescopes at the La Silla Observatory and the Las Campanas Observatory, both in Chile, the researchers mapped the motions of more than 400 stars up to 13,000 light-years from the sun.

They used those measurements to calculate the mass of matter in a volume four times larger than had been considered before at this level of precision. Under the standard dark matter theory, there should be at least as much dark matter as visible matter in this region. "Contrary to our expectations, there is none," Moni Bidin says. "The result matches the visible mass strongly."

Dark matter may be an illusion caused by the quantum vacuum

Dark matter may be an illusion caused by the quantum vacuum: “I suggest a third way, without introducing dark matter and without modification of the law of gravity.”
His ideas (like those in the previous paper) rest on the key hypothesis that matter and antimatter are gravitationally repulsive, which is due to the fact that particles and antiparticles have gravitational charge of opposite sign...
“Concerning gravity, mainstream physics assumes that there is only one gravitational charge (identified with the inertial mass) while I have assumed that, as in the case of electromagnetic interactions, there are two gravitational charges: positive gravitational charge for matter and negative gravitational charge for antimatter,” Hajdukovic explained...
He also derives the famous Tully-Fisher relation as a consequence of the gravitational repulsion between matter and antimatter. This relation is an empirical law based on numerical data collected by numerous observations of galaxies and clusters of galaxies, and is still unexplained in the framework of dark matter hypotheses.

[1104.3654] Cosmological extrapolation of MOND

[1104.3654] Cosmological extrapolation of MOND: "Regime of MOND, which is used in astronomy to describe the gravitating systems of island type without the need to postulate the existence of a hypothetical dark matter, is generalized to the case of homogeneous distribution of usual matter by introducing a linear dependence of the critical acceleration on the size of region under consideration. We show that such the extrapolation of MOND in cosmology is consistent with both the observed dependence of brightness on the redshift for type Ia supernovae and the parameters of large-scale structure of Universe in the evolution, that is determined by the presence of a cosmological constant, the ordinary matter of baryons and electrons as well as the photon and neutrino radiation without any dark matter."

More Evidence Against Dark Matter? - ScienceNOW

More Evidence Against Dark Matter? - ScienceNOW: McGaugh gathered data from various sources on 47 galaxies that contain more hydrogen gas than stars. The mass of the gas can then be estimated directly. McGaugh made a plot of visible mass versus rotation speed for the galaxies. He then plotted the prediction that comes straight out of MOND in a few lines of algebra. The MOND line went right through the data. "You draw the line and the data fall right on it," McGaugh says...
 "The real strength of Stacy's paper is that it points to something that can't be explained in cold dark matter, irrespective of whether MOND is right."

Black Holes Not Affected by Dark Matter, Say Astrophysicists - Technology Review

Black Holes Not Affected by Dark Matter, Say Astrophysicists - Technology Review: "But in the fine tradition of science, this clears up one mystery only to reveal another. If dark matter has this powerful gravitational influence, why doesn't it form into black holes?

Nobody knows. But there is another group of astronomers who will be studying this result with interest. These guys think dark matter is an unnecessary invention. Instead, they say, the rotation of galaxies can be explained if the force of gravity is stronger over these galactic distances.

So according to them there is a simpler explanation for the absence of a link between dark matter and black holes: it's that dark matter doesn't exist."