Black holes could be ideal dark matter labs

The gamma rays produced when dark matter particles collide are rare and difficult to observe. A new NASA simulation shows how the power of black holes could provide conditions for greater detection.

Published: June 24, 2015 at 12:00 pm

An image layering frames from the simulation to increase the number of dark matter particles. Particles are gray spheres attached to trails representing their motion. Redder trails show where particles are more affected by the black hole’s gravitation. The black sphere at the centre is the black hole’s event horizon. The ergosphere is shown in teal. Credit: NASA Goddard Scientific Visualiztion Studio


Black holes could provide a natural, galactic laboratory to help scientists understand more about dark matter.

This is the conclusion drawn from a NASA computer simulation showing dark matter particles colliding within a black hole and producing strong gamma-ray light.

The actual detection of this phenomenon in reality could reveal more about black holes and the nature of the elusive substance known as dark matter.

Credits: NASA's Goddard Space Flight Center

“While we don’t yet know what dark matter is, we do know it interacts with the rest of the Universe through gravity, which means it must accumulate around supermassive black holes,” says Jeremy Schnittman, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

“A black hole not only naturally concentrates dark matter particles, its gravitational force amplifies the energy and number of collisions that may produce gamma rays.”

Schnittman’s simulation follows the orbits of hundreds of millions of dark matter particles and the gamma rays produced when they collide near a black hole.

It represents dark matter as weakly interacting massive particles (WIMPS), which are the current leading candidates in the search for what dark matter actually is.

In the model, these WIMPS smash into each other and are converted to gamma rays, the most energetic form of light.

The rarity of these collisions has led scientists to turn to black holes as a space where WIMPs can be forced together, to increase the likelihood of this process occurring.

The collisions happen just outside the black hole’s event horizon - the point beyond which nothing can escape – in the ergosphere.

Here, the black hole’s rotation forces everything to move in the same direction at nearly speed of light.

This allows high-energy collisions to occur further from the event horizon and increases the chance that any gamma rays produced can escape the black hole.

The simulation builds on previous work by depicting the production of gamma rays with higher energies and a greater chance of escape and detection than thought possible.

Schnittmann has identified previously unrecognised paths and collisions, producing gamma rays with a peak energy 14 times higher than that of the original particles.

Schnittman hopes this research could lead to the detection of an annihilation signal from dark matter around a supermassive black hole.

These annihilation signals occur when WIMPS collide with each other and convert into gamma rays, and could lead to the observable detection of dark matter.

“The simulation tells us there is an astrophysically interesting signal we have the potential of detecting in the not too distant future, as gamma-ray telescopes improve,” Schnittman says.


“The next step is to create a framework where existing and future gamma-ray observations can be used to fine-tune both the particle physics and our models of black holes.”


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