4 ms·

I want to know if the jets are made up of material that is swirling towards the black hole from the accretion disk but get caught up in the magnetic helix (a) b

by hcrisp 5y ago

I want to know if the jets are made up of material that is swirling towards the black hole from the accretion disk but get caught up in the magnetic helix (a) before it reaches the event horizon, or (b) after it passes the event horizon. If the former, then it's not as impressive since then nothing can escape a black hole except via Hawking radiation. If the latter, then this seems like quite a novel mechanism to prevent infinite black hole growth. The illustrations in the article don't provide an answer, though, since the details ends right where it ought to provide insight. The article does mention that the new paper puts doubt on the idea that nothing can escape a black hole, but I still didn't see any direct mention of the event horizon question.

db48x 5y ago
Nothing can return after having crossed the event horizon. Gravity bends space and time, and in particular it changes which direction the time axis points. In a black hole, the time axis is bent all the way over so that it points directly at the singularity. All paths that enter the black hole must end at the singularity, because to do otherwise would require going backwards in time or faster than the speed of light.
- hcrisp 5y ago
  Can you then explain what the author means when she says, "a voltage that draws energy up and out of the hole and along the helix. This, they claimed, is the jet — and a big asterisk on the naive notion that nothing escapes black holes"?
  - wumpus 5y ago
    Black holes have spin, and this process is expected to slow the black hole spin, which takes energy out of it. It's not the only known way to slow black hole spin.
  - db48x 5y ago
    The statement doesn’t mean anything because it was written by a reporter and reporters generally don’t understand what they are writing about, especially in the modern era, and especially in regards to scientific concepts. The magnetic fields can accelerate matter from the accretion disk and turn it into a jet headed away from the black hole, there’s nothing wrong with that. Maybe matter can be created by photon–photon interactions in the photon ring, and that matter can be accelerated into a jet by the magnetic field. Either way, no matter has exited the black hole; the jet is made of matter that avoided entering the event horizon. Black holes have only three macroscopic quantities which are observable from the outside: mass, rotational kinetic energy, and electric charge. Since it would be pretty hard to arrange for matter of only one electric charge to fall into a black hole, the charge of the average black hole is believed to be pretty much neutral at all times. The mass of the black hole is inaccessible, because it is concentrated at the singularity. Or possibly in the firewall, if black holes have firewalls. That leaves the rotational kinetic energy as the source of the energy that powers the jets. The jets would last until the rotation of the black hole slows enough that the magnetic fields aren’t twisted enough to maintain them.

by hcrisp 5y ago

db48x 5y ago

Nothing can return after having crossed the event horizon. Gravity bends space and time, and in particular it changes which direction the time axis points. In a black hole, the time axis is bent all the way over so that it points directly at the singularity. All paths that enter the black hole must end at the singularity, because to do otherwise would require going backwards in time or faster than the speed of light.

hcrisp 5y ago
Can you then explain what the author means when she says, "a voltage that draws energy up and out of the hole and along the helix. This, they claimed, is the jet — and a big asterisk on the naive notion that nothing escapes black holes"?
- wumpus 5y ago
  Black holes have spin, and this process is expected to slow the black hole spin, which takes energy out of it. It's not the only known way to slow black hole spin.
- db48x 5y ago
  The statement doesn’t mean anything because it was written by a reporter and reporters generally don’t understand what they are writing about, especially in the modern era, and especially in regards to scientific concepts. The magnetic fields can accelerate matter from the accretion disk and turn it into a jet headed away from the black hole, there’s nothing wrong with that. Maybe matter can be created by photon–photon interactions in the photon ring, and that matter can be accelerated into a jet by the magnetic field. Either way, no matter has exited the black hole; the jet is made of matter that avoided entering the event horizon. Black holes have only three macroscopic quantities which are observable from the outside: mass, rotational kinetic energy, and electric charge. Since it would be pretty hard to arrange for matter of only one electric charge to fall into a black hole, the charge of the average black hole is believed to be pretty much neutral at all times. The mass of the black hole is inaccessible, because it is concentrated at the singularity. Or possibly in the firewall, if black holes have firewalls. That leaves the rotational kinetic energy as the source of the energy that powers the jets. The jets would last until the rotation of the black hole slows enough that the magnetic fields aren’t twisted enough to maintain them.