Globular Clusters and Gravity

Using globular clusters to test gravity in the weak acceleration regime

We report on the results from an ongoing program aimed at testing Newton's law of gravity in the low acceleration regime using globular clusters. It is shown that all clusters studied so far do behave like galaxies, that is, their velocity dispersion profile flattens out at large radii where the acceleration of gravity goes below 1e-8 cm/s/s, instead of following the expected Keplerian fall off. In galaxies this behavior is ascribed to the existence of a dark matter halo. Globular clusters, however, do not contain dark matter, hence this result might indicate that our present understanding of gravity in the weak regime of accelerations is incomplete and somehow incorrect.

Dark Matter in Galaxies

Dark Matter in Galaxies: Conference Summary

Abstract. The competition between CDM and MOND to account for
the ‘missing mass’ phenomena is asymmetric. MOND has clearly demonstrated that a characteristic acceleration a0 underlies the data and understanding what gives rise to a0 is an important task. The reason for MOND’s success may lie in either the details of galaxy formation, or an advance in fundamental physics that reduces to MOND in a suitable limit. CDM has enjoyed great success on large scales. The theory cannot be definitively tested on small scales until galaxy formation has been understood because baryons either are, or possibly have been, dominant in all small-scale objects. MOND’s predictive power is seriously undermined by its isolation from the rest of physics. In view of this isolation, the way forward is probably to treat CDM as an established theory to be used alongside relativity and electromagnetism in efforts to understand the formation and evolution of galaxies.

Reionization Review

The Frontier of Reionization: Theory and Forthcoming Observations

The cosmic microwave background provides an image of the Universe 0.4 million years after the big bang, when atomic hydrogen formed out of free electrons and protons. One of the primary goals of observational cosmology is to obtain follow-up images of the Universe during the epoch of reionization, hundreds of millions of years later, when cosmic hydrogen was ionized once again by the UV photons emitted from the first galaxies

Under the assumption that general relativity describes the evolution of the Universe, the measured CMB anisotropies indicate conclusively that most of the matter in the Universe must be very weakly coupled to electromagnetism and hence cannot be the matter that we are made of (baryons). This follows from the fact that prior to hydrogen recombination, the cosmic plasma was coupled to the radiation through Thomson scattering. Small-scale fluctuations were then damped in the radiation-baryon fluid by photon diffusion. The damping is apparent in the observed suppression of the CMB anisotropies on angular scales well below a degree on the sky, corresponding to spatial scales much smaller than 200 comoving Mpc. To put this scale in context, the matter that makes up galaxies was assembled from scales of < 2Mpc. In order to preserve the primordial inhomogeneities that seeded the formation of galaxies, it is necessary to have a dominant matter component that does not couple to the radiation fluid

Empathy, Gender, Fantasy and Fiction

High Empathy (Mostly Women), Low Empathy (Mostly Men) and the Movies in the New York Times.

To test empathy levels and the subjects’ reactions to various melodramas, the researchers turned to several classic short stories, like “The Last Leaf” by O. Henry, that include struggles against adversity and melancholy plot twists.

People with low empathy (mostly men) who believed the stories to be fantasies liked them much better than those who were told the stories were factual. The reverse held true for people with high empathy, who were mostly women.

Another surprising observation from the study: not one of the 492 students tested reported having read or heard any of the stories, even though some are quite prominent. “I was appalled,” Professor Argo said.