Black Holes May be Perfect Dark Matter Labs

Black holes may actually be ideal labs for studying dark matter. A new NASA computer simulation reveals that dark matter particles colliding in the extreme gravity of a black hole can produce strong, potentially observable gamma-ray light. Detecting this emission would provide astronomers with a new tool for understanding black holes and the nature of dark matter.

"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," said Jeremy Schnittman, one of the researchers, in a news release. "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."

In this latest study, the researchers created a computer simulation to follow the orbits of hundreds of millions of dark matter particles, as well as the gamma ray produced when they collide, in the vicinity of a black hole. The scientists found that some gamma rays escaped with energies far exceeding what had previously been thought to be the theoretical limits.

In the simulation, dark matter took the form of Weakly Interacting Massive Particles (WIMPS), which are the leading candidate of what dark matter could be. In this model, WIMPs that crash into other WIMPs mutually annihilate and convert into gamma rays, the most energetic form of light. But these collisions are extremely rare under normal circumstances.

Over the past few years, researchers have turned to black holes as dark matter concentrators, where WIMPs can be forced together in a way that increases both the rate and energies of collisions. The concept is a variant of the Penrose process, which is a mechanism for extracting energy from a spinning black hole. The faster the black hole spins, the greater the potential energy gain.

"Previous work indicated that the maximum output energy from the collisional version of the Penrose process was only about 30 percent higher than what you start with," said Schnittman. This suggested that the Penrose process might never be seen from a supermassive black hole.

In the latest model, though, the researchers tracked the positions and properties of hundreds of millions of randomly distributed particles as they collided and annihilated each other near a black hole.

"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," said Schnittman. "The next step is to create a framework where existing and future gamma-ray observations canbe used to fine-tune both the particle physics and our models of black holes."

The findings are published in the journal Physical Review Letters.

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