3 ms·

The key part: As it happens, the disk that formed around the black hole was face-on to us, so one of those beams was essentially aimed directly at us. Anyone

by iwwr 16y ago

The key part: As it happens, the disk that formed around the black hole was face-on to us, so one of those beams was essentially aimed directly at us. Anyone know just how focused these beams are?

teamonkey 16y ago
IIRC it depends on the black hole. Right now there isn't a precise formula for it. The breakup of the star would form an accretion disc, the jets would form at the axis of rotation. The formation of the jets are classically mechanical (conservation of angular momentum by various means) and so the focus of the jet depends on the speed of the matter being ejected, the amount of matter being ejected and the mass of the black hole. Moreover, the matter falling into the black hole is heated to plasma level and so there is very strong magnetic activity. As the accretion disc spins, the magnetic field lines twist along the axis of rotation - the same axis as the ejected matter. This has the upshot of focusing the jets very tightly. http://en.wikipedia.org/wiki/Black_hole#Accretion_of_matter http://en.wikipedia.org/wiki/Black_hole#Accretion_of_matter
lutorm 16y ago
I'm not sure about these beams, but at least GRBs from collapsing stars come from a relativistic shock wave with gamma of ~1000, IIRC. Such high gamma gives a very collimated beam of radiation, of order 1/gamma, due to relativistic beaming. So taking 1/1000 radians as a ballpark value, 1mrad is about the divergence of a typical laser. (Laser pointers have slightly higher divergence due to the short cavity, but things like He-Ne lasers are typically 1mrad.)
fhars 16y ago
Somebody on one of the blogs mentioned about 5 degrees, make that 3.6 degrees, which is a hundredth of the full circle or 0.06 rad, and since for such values x is approximately tan(x), it would be about 4 billion times 0.06 or 240 million lightyears narrow at our distance.

by iwwr 16y ago

The key part: As it happens, the disk that formed around the black hole was face-on to us, so one of those beams was essentially aimed directly at us. Anyone know just how focused these beams are?

teamonkey 16y ago

IIRC it depends on the black hole. Right now there isn't a precise formula for it. The breakup of the star would form an accretion disc, the jets would form at the axis of rotation. The formation of the jets are classically mechanical (conservation of angular momentum by various means) and so the focus of the jet depends on the speed of the matter being ejected, the amount of matter being ejected and the mass of the black hole. Moreover, the matter falling into the black hole is heated to plasma level and so there is very strong magnetic activity. As the accretion disc spins, the magnetic field lines twist along the axis of rotation - the same axis as the ejected matter. This has the upshot of focusing the jets very tightly. http://en.wikipedia.org/wiki/Black_hole#Accretion_of_matter http://en.wikipedia.org/wiki/Black_hole#Accretion_of_matter

lutorm 16y ago

I'm not sure about these beams, but at least GRBs from collapsing stars come from a relativistic shock wave with gamma of ~1000, IIRC. Such high gamma gives a very collimated beam of radiation, of order 1/gamma, due to relativistic beaming. So taking 1/1000 radians as a ballpark value, 1mrad is about the divergence of a typical laser. (Laser pointers have slightly higher divergence due to the short cavity, but things like He-Ne lasers are typically 1mrad.)

fhars 16y ago

Somebody on one of the blogs mentioned about 5 degrees, make that 3.6 degrees, which is a hundredth of the full circle or 0.06 rad, and since for such values x is approximately tan(x), it would be about 4 billion times 0.06 or 240 million lightyears narrow at our distance.