Synopsis

Black Hole Tests of Fermionic Dark Matter

Physics 8, s137
Gamma-ray observations of dark matter spikes near supermassive black holes provide a test of fermionic dark matter models.
NASA/JPL-Caltech

One of the principal strategies to indirectly detect dark matter is to search for the photons produced when it annihilates. Such searches look for gamma rays or x rays in regions of the sky where dark matter is known to be abundant. Researchers at the University of Illinois at Urbana–Champaign have proposed to look inside dark matter spikes induced by the gravitational pull of supermassive black holes. Such measurements could test so called p-wave dark matter models.

Most astrophysical dark matter searches rely on the assumption that the annihilation cross section does not depend on particle velocity. However, there are models in which dark matter annihilates via p-wave interactions—that is, the pair of annihilating particles has initial angular momentum one—leading to a cross section proportional to the velocity squared. This happens, for instance, in models where fermionic dark matter annihilates to pairs of spinless bosons. Since the dark matter temperature, and hence its velocity, is believed to be low, p-wave signatures were largely inaccessible by current searches.

However, near a supermassive black hole like the Milky Way's Sagittarius A*, dark matter is expected to cluster into a density spike. Within such a spike, the density and velocities of dark matter particles could be sufficient for thermal p-wave annihilation to produce a detectable gamma-ray signal. Using two prototypical p-wave models and gamma-ray data from NASA’s Fermi Large Area Telescope, the researchers found no evidence for p-wave dark matter and constrained its annihilation cross section for the first time. Their analysis suggests that a dedicated search for sharp gamma-ray lines near Sagittarius A* can improve these constraints.

This research is published in Physical Review Letters.

–Kevin Dusling


Subject Areas

Particles and FieldsAstrophysicsGravitation

Related Articles

Sterile Neutrino Down but Not Completely Out
Particles and Fields

Sterile Neutrino Down but Not Completely Out

Neutrino experiments place the most stringent limits to date on a hypothetical fourth neutrino, but the possibility that such a particle exists remains open. Read More »

Powdering Up for Neutrinos
Particles and Fields

Powdering Up for Neutrinos

The search for neutrinos from past supernovae is getting an upgrade as Japan’s Super-Kamiokande experiment begins adding gadolinium powder to its giant water-based detector. Read More »

Could Planet Nine Be a Black Hole?
Astrophysics

Could Planet Nine Be a Black Hole?

While astronomers look for a ninth planet to explain orbits in the outer solar system, a duo explores the possibility that the mystery object is a primordial black hole. Read More »

More Articles