Starts With A Bang

Black Holes As Dark Matter? Here’s Why The Idea Falls Apart (Synopsis)

A massive black hole accreting matter off of a nearby star. Image credit: NASA/JPL-Caltech.

“[The black hole] teaches us that space can be crumpled like a piece of paper into an infinitesimal dot, that time can be extinguished like a blown-out flame, and that the laws of physics that we regard as ‘sacred,’ as immutable, are anything but.” -John Wheeler

Dark matter is one of the biggest mysteries in the Universe. We can feel its gravitation, we can see its effects on galaxies, clusters and the large-scale structure of the Universe. But when it comes to very small scales, we haven’t been able to detect dark matter, either directly or indirectly, leading us to wonder at what it’s mysterious nature might be.

Illustration of a clumpy dark matter halo around the baryons in a galaxy. Image credit: NASA, ESA, and T. Brown and J. Tumlinson (STScI).

While the notion that primordial black holes could be the dark matter has been disfavored by a large suite of observations, the LIGO detection of two merging black holes — of a particular, unusual mass — has rekindled interest in that nearly-abandoned idea. Could the fluctuations in the cosmic infrared background actually be due to these primordial black holes, and could they make up 100% of the dark matter?

Left: An infrared view of the sky in Ursa Major. Right: an enhanced view with known sources masked, showing fluctuations of the infrared background. Credits: NASA/JPL-Caltech/A. Kashlinsky (Goddard).

The answer is almost definitely “no,” and I’ve got the scoop as to why!