Do Black Hole Masses Grow as the Universe Does?

Relativists - those physicists who study General Relativity - often report their work more like Mathematicians than typical scientists. Astrophysicists and Astronomers often apply their work to put these solutions into a realistic context.

For example, black holes are fine, but what would they look like if we actually found them in space?

These kind of contextual studies have the potential to expose problems with our knowledge of the fundamentals. One big issues that has plagued astrophysicists lately has been the distribution of black hole masses.

Given the known and studied production mechanisms - as well as the known evolution of the universe - black holes were expected to fall into two categories: small, “stellar-mass” black holes from recent Supernovae and “supermassive” black holes at the center of galaxies. Despite this prediction, current astronomical evidence suggests that so-called “intermediate mass black holes” are prevalent in the universe. The problem? We don’t know how such black holes might form, at least not at the observed rate.

Physicists at the University of Hawai`i, together with colleagues from Chicago and Michigan have proposed a resolution that would augment the fundamentals: the masses of black holes could grow as the universe does.

Despite reeking of Hoyle’s “steady state” model for the universe, it does have curious implications for the geometric nature of space time. The physical size of black holes - their surface area - are known to scale with their mass. Typically we assume that mass is independent of cosmological expansion. In particular, we assume that the expansion of the universe has nothing to do with individual objects.

Yet, if the surface area of the black hole’s event horizon was some how coupled to the expansion of the universe, this would suggest that the effective mass of those black holes would also have to increase.

For now, the cosmological coupling idea is both a speculative and toy model. The model studied by the authors involves a small, anomalous scaling, suggestive of some quantum or an otherwise collective effect. It’s a very interesting proposition to the least.