Purdue researchers uncover what makes black holes shine

2017-08-11

WEST LAFAYETTE, Ind. — Researchers at Purdue University have successfully simulated powerful flows of plasma leaving a black hole, bringing us one step closer to understanding the complicated relationship between supermassive black holes and their host galaxies.

These outflows of plasma are called jets, and they convert up to half of their energy into radiation. Jets are extremely variable and poorly understood; they flare erratically and their bright glow can last anywhere from hours to months. When they point toward us, they can be observed by any satellite or detector on Earth.

A snapshot is shown from simulations of jets in 3 dimensions following the jet over three orders of magnitude in distance (from Barniol Duran, Tchekhovskoy & Giannios 2017). The location at which the external medium density changes induces instabilities in the jet and triggers extensive dissipation of magnetic energy.

"The reason that jets shine visible electromagnetic radiation remains a mystery," said Dimitrios Giannios, a professor of physics and astronomy at Purdue. "Scientists have long speculated that processes like shockwaves or instabilities in the magnetic field may cause the observed emission."

Jets are prone to various instabilities, but the magnetic kink instability is the most likely cause of dissipation. Here, the researchers compared the instabilities experienced by two different kinds of jets: headed and headless.

In a headed jet, the black hole is surrounded by gas everywhere, but in a headless jet, there is little gas along the polar region of the black hole. Headed jets were much more likely to be impacted by the magnetic kink instability because the jet has to drill a hole to make it through the gas, slowing it down and strongly winding up its magnetic field.

"These are prime locations for the jets to shine," Giannios said.

Black holes eject large amounts of light and gas, which affects how the whole galaxy forms stars. However, a process still seems to regulate how the galaxy and black hole grow together. Understanding how jets shine and interact with the gas in the galaxy is essential to deciphering this relationship, said Giannios. 

The study is available here. 

Writer: Kayla Zacharias, 765-494-9318, kzachar@purdue.edu

Source: Dimitrios Giannios, 765-494-5194, dgiannio@purdue.edu