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These accretion discs are always described as emitting extreme amounts of energy, but it is never clear what makes them do this. We know stars convert mass to e

These accretion discs are always described as emitting extreme amounts of energy, but it is never clear what makes them do this. We know stars convert mass to energy by fusion under extreme pressure and temperature in their cores. Does this accretion disc have extreme pressure domains where fusion happens? Or is it more like streams of matter being accelerated to collide like a synchrotron, with no pressure and only massed velocity driving nuclei to fuse, a beam striking a target? Or are we getting extreme pressure via confinement in twisted magnetic fields, like what is attempted in Tokamaks? And, is the energy coming from fusion at all? Could gravitation alone account for the energy released, without fusion occurring in the disc?

nh23423fefe 4y ago
from Foundations of Black Hole Accretion Disk Theory https://link.springer.com/article/10.12942/lrr-2013-1 https://link.springer.com/article/10.12942/lrr-2013-1 > The radiation we receive from quasars and microquasars comes not from the black holes themselves, but instead originates in the accretion disks which surround themFootnote6 (see Figure 1). In these accretion disks, angular momentum is gradually removed by some presumably (although not necessarily [48]) dissipative process, causing matter to spiral down into the black hole, converting its gravitational energy into heat, and then, by various processes, radiating this energy.Footnote7 The radiation subsequently leaks through the disk, escapes from its surface, and travels along trajectories curved (in space) by the strong gravity of the black hole, eventually reaching our telescopes. So not fusion, the energy is gravitational potential.
- moloch-hai 4y ago
  It seems implausible, on its face, that the by-far most energetic processes in the universe are driven by the by-far weakest force in the universe. We know that electromagnetic fields are deeply involved in focusing the jet -- beam, really -- coming out. It beggars imagination to insist they can have no further role. Do we have any reason to believe no fusion is occurring in the process?

nh23423fefe 4y ago

from Foundations of Black Hole Accretion Disk Theory https://link.springer.com/article/10.12942/lrr-2013-1 https://link.springer.com/article/10.12942/lrr-2013-1 > The radiation we receive from quasars and microquasars comes not from the black holes themselves, but instead originates in the accretion disks which surround themFootnote6 (see Figure 1). In these accretion disks, angular momentum is gradually removed by some presumably (although not necessarily [48]) dissipative process, causing matter to spiral down into the black hole, converting its gravitational energy into heat, and then, by various processes, radiating this energy.Footnote7 The radiation subsequently leaks through the disk, escapes from its surface, and travels along trajectories curved (in space) by the strong gravity of the black hole, eventually reaching our telescopes. So not fusion, the energy is gravitational potential.

moloch-hai 4y ago
It seems implausible, on its face, that the by-far most energetic processes in the universe are driven by the by-far weakest force in the universe. We know that electromagnetic fields are deeply involved in focusing the jet -- beam, really -- coming out. It beggars imagination to insist they can have no further role. Do we have any reason to believe no fusion is occurring in the process?