Black Holes are the new Dark Matter Laboratories

Asymmetric black hole glow from high-energy gamma rays being flung towards earth. Jeremy Schnittman/NASA.

The hunt for dark matter has still left us very much in the dark about the elusive substance. However, an astrophysicist from NASA has thought up a new idea for a dark matter laboratory... and it's not your conventional lab. In fact, it's situated around one of the most massive objects in the universe: a black hole.

Astrophysicist Jeremy Schnittman came to this conclusion after creating a computer model that simulates how dark matter particles might interact with the extreme gravity around a black hole. Based on this simulation, he is hopeful that there is a way to detect these particles. The study is published in The Astrophysical Journal

In Schnittman's experiment, the dark matter particles were modeled on WIMPs (Weakly Interacting Massive Particles). As the name suggests, these are particles with mass that zoom through the universe without interacting with anything else. It is possible for WIMPs to interact with other WIMPs and annihilate to form gamma rays. However, the probability of this happening is like two bullets hitting each other straight on in a crossfire and decimating each other. So that's quite small.

One place that Schnittman predicts we will see many WIMPs close together – thus increasing the chance of a collision – is around black holes. WIMPs interact with the force of gravity, and there is a lot of gravitational attraction humming around black holes.

For example, to escape the Earth's gravitational pull, you have to exit at a speed of 6.8 miles per second (11 kps). However, even light, which travels at the universal speed limit of roughly 186,000 mps (300,000 kps), can't escape a black hole. 

Schnittman thinks that this powerful gravitational attraction will make black holes a hotspot for WIMPs and make the probability of a collision much higher. There are a few other features that make collisions more likely around black holes, too. Black holes rotate in space, forming a region around them called an ergosphere. Any particle that enters this region is forced to rotate in the same direction as the black hole at nearly the speed of light. The faster the black hole spins, the larger the ergosphere can be, which means that collisions can occur further away from the black hole's event horizon: the point where nothing can escape. 

Any collisions that occur in this ergosphere will produce gamma rays that can escape the black hole, which we can then possibly detect. Supermassive black holes, with the fastest rotation and therefore the largest ergospheres, seem like the most likely candidates for spotting these fleeing particles.

 

 

Video explaining Schnittman's research. NASA.

Schnittman's model shows that due to the rotation of the black hole, we are more likely to see the gamma rays from one side. In the model, this is the left side of the black hole, which is spinning towards us and flinging the gamma rays produced towards Earth. The result is an asymmetric glow around the black hole in the gamma spectrum that we could possibly detect with the right equipment.

This model may help scientists create experiments that allow mankind to confirm the existence of dark matter: a challenge that has rattled the brains of many a physicist. To spot the products of dark matter, collisions would be the first step towards maybe even discovering another chapter in the origins of the universe. It is thought that dark matter formed the first clumps of matter in the universe. The gravitational pull from these dark matter clumps is what caused the first visible matter dust clouds to form, which in turn formed stars, planets and galaxies. And us!

[Via NASA]

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