# How can a black hole eject plasma? [duplicate]

This image from an online Italian newspaper shows photographs of one of the most powerful phenomena in the cosmos.

Nothing, not even at the speed of light $$c$$, can escape a black hole one it has been caught. So how is it possible mathematically that a black hole, which "swallows" the stars and gas approaching its powerful accretion disk, can then eject some of the gas into two thin jets of plasma at speeds $$V_{pl}$$ close to the speed of light?

• Proposed in 1977, not yet verified. But whatever the answer is, it is not $v_{pl}>c$: en.wikipedia.org/wiki/Blandford–Znajek_process
– JEB
Apr 7, 2020 at 15:04
• @JEB Thank you for your comment. Mine was just a hypothesis to be tempted to say that $v_{\text{pl}}>c$. I have not understood your link. Apr 7, 2020 at 15:09
• I think the "dash" was some non-standard dash that wiki-P uses, that this little comment box refused to interpret. – vs -.
– JEB
Apr 7, 2020 at 15:12
• BTW: My relativistic magneto hydrodynamics class was taught by Blanford in '88, and I didn't understand it then, and haven't made progress in the meantime.
– JEB
Apr 7, 2020 at 15:21
• How does it differ from asking how jets originate from a black hole? Apr 7, 2020 at 15:34

The black hole is defined by its event horizon. This is the point at which the escape velocity reaches $$c$$. But the accretion disc forms outside the event horizon, so stuff can still escape from it. It is this outer stuff that finds its way into the jets, super-accelerated beyond escape velocity by magnetic fields being dragged round the hole.
If the escape velocity at the point of acceleration outside the black hole is $$V_s$$ then $$c > V_{pl} > V_s$$.