Although the generation of plasma turbulence by the MRI is well understood, still unsolved is how MRI-driven turbulence is dissipated in the hot and diffuse conditions of the plasma around the black hole. The heated plasma then emits this energy as radiation. These fluctuations interact and generate turbulence, which cascades energy in the plasma from large to small scales, where the turbulence dissipates into heat. That motion is unstable, generating fluctuations in both the magnetic field and the flow of the plasma. The mechanism is as follows: A magnetic-field-driven disturbance, called a magnetorotational instability (MRI), causes plasma close to the black hole-and thus faster moving-to fall inward, while plasma further away-and thus slower-moves outward. This finding implies that it should be possible to distinguish observationally the mechanisms that govern this heating, a critical step in developing a more complete understanding of black hole physics.Īstrophysicists have a general idea of how the plasma around a black hole taps energy from a black hole’s gravitational potential. Now, Joonas Nättilä and Andrei Beloborodov of Columbia University identify through simulations that plasma heated by the dissipation of so-called “Alfvénic” turbulence should radiate via a different process than that heated by other routes, giving it different spectral properties. The nature of this emitted radiation depends strongly on the way that energy is generated in the plasma, but those heating mechanisms remain unidentified. A black hole becomes visible to astronomers when its encircling plasma falls inward, causing this ionized gas to heat up and emit radiation. ×īlack holes are some of the most enigmatic objects in the Universe, harboring intense magnetic fields and colossal gravitational forces that even light cannot escape.
Schnittman Figure 1: A simulation showing the turbulent plasma around a black hole.
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