On 19/01/2017 03:53, wrote:
Example object, Pictor A
http://chandra.harvard.edu/photo/2016/pictora/

in particular, the x ray Chandra image:
http://chandra.harvard.edu/photo/201...ctora_xray.jpg

Question 1:

Has anyone proposed any model that describes a mechanism to produce
a single BH jet, or, alternating BH jets (e.g. the jet shoots one
way for a while, then the other way for a while, alternating back
and forth)?

The only way I could see that there might be a significant asymmetry is
when a BH has run out of matter to consume and the last gulp wasn't
evenly distributed so that one pole runs out before the other. This
would be quite rare and only during the transition to quiescence.

Otherwise for an active BH I think the standard model pretty much
requires that the jets are symmetric. See for example:

http://ned.ipac.caltech.edu/level5/Carilli/Car2_1.html

And go back to contents for a nice review of Cygnus A.

However time of flight considerations could mean that there hasn't yet
been time for the light from the more distant hotspot of two to reach us
in the case of a source where the jet is almost pointing at us.

Question 2:

*IF* there are 2 jets active, and both are active for the same
duration, then wouldn't we observe a pair of Hot Spots of the same
size? We clearly see a hot spot on the right side, but there isn't
one on the left side (there are other sources, but they are all
smaller in angular size, and there isn't a source at the location
of the protrusion where the jet recently had been.)

The main reasons for not seeing the other hotspot I can think of are
either relativistic beaming making the one coming towards us appear very
much brighter or something in the way (or a bit of both).

The angle the jet makes with our line of sight affects how they look.

If one is to contend that the jet wanders, and that's why we don't
see the counter hot spot because it recently moved from where the
optical / radio extension is, then the same must be true for the
primary jet coming toward us.............is there an example of a
primary jet coming toward us *without* a hot spot?

I suspect relativistic beaming makes this very unlikely.

Question 3:

If the primary jet on the right side were to turn off at time 0,
how long would it take for the heated x ray gas to cool off so that
we no longer saw a hot spot? tens, thousands, millions of years?
I have no sense on time scale for this intergalactic gas cooling
process so any guesses appreciated.

3C452 sort of answers this slightly in that there are faint relics of
much older radio lobes seen at 325MHz but not at GHz and some distance
far out from the modern hotspots and brighter lobes associated with
them. See for example:

http://iopscience.iop.org/article/10...8205/765/1/L11

As high resolution high dynamic range aperture synthesis images become
available at lower frequencies I expect more of these will be found.

The point is, if the counter jet hot spot has cooled due to motion,
the cooling time is indicative of the jet pointing change velocity
if there is no observable hot spot. But the same must then apply
to all of the many similar objects that do not show counter jet hot
spots.

Am I missing something important here? What is it?

One thing is that the light travel time to us from the furthest hotspot
is significantly longer than for the nearest one. So we are seeing the
two hotspots being illuminated by beams emitted from the BH at two quite
different times. If the beam wasn't steady then it is possible that at
the time we see the more distant spot the beam was quiescent.

I am out of date on some of this stuff but the fundamentals probably
haven't changed. Corrections and refinements welcomed.

BTW to the OP it would help point you at the right material if you gave
some idea of the level of mathematics and physics that you understand.

--
Regards,
Martin Brown