Selections from 2016: Primordial Black Holes as Dark Matter

Editor’s note: In these last two weeks of 2016, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded papers published in AAS journals this year. The usual posting schedule will resume after the AAS winter meeting.

LIGO Gravitational Wave Detection, Primordial Black Holes, and the Near-IR Cosmic Infrared Background Anisotropies

Published May 2016


Main takeaway:

A study by Alexander Kashlinsky (NASA Goddard SFC) proposes that the cold dark matter that makes up the majority of the universe’s matter may be made of black holes. These black holes, Kashlinsky suggests, are primordial: they collapsed directly from dense regions of the universe soon after the Big Bang.

Why it’s interesting:

This model would simultaneously explain several observations. In particular, we see similarities in patterns between the cosmic infrared and X-ray backgrounds. This would make sense if accretion onto primordial black holes in halos produced the X-ray background in the same regions where the first stars also formed, producing the infrared background.

What this means for current events:

In Kashlinsky’s model, primordial black holes would occasionally form binary pairs and eventually spiral in and merge. The release of energy from such an event would then be observable by gravitational-wave detectors. Could the gravitational-wave signal that LIGO detected last year have been two primordial black holes merging? More observations will be needed to find out.


A. Kashlinsky 2016 ApJL 823 L25. doi:10.3847/2041-8205/823/2/L25