Single vs Double hot spots for BH Jets? (e.g. Pictor A)

[r***@gmail.com]

Example object, Pictor A
http://chandra.harvard.edu/photo/2016/pictora/

in particular, the x ray Chandra image:
Loading Image...

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)?

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.)

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?

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.

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?

Thanks,

rt

[Martin Brown]

Post by r***@gmail.com
Example object, Pictor A
http://chandra.harvard.edu/photo/2016/pictora/
http://chandra.harvard.edu/photo/2016/pictora/pictora_xray.jpg
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.

Post by r***@gmail.com
*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.

Post by r***@gmail.com
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.

Post by r***@gmail.com
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/10.1088/2041-8205/765/1/L11

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

Post by r***@gmail.com
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.

[r***@gmail.com]

Post by Martin Brown

Post by r***@gmail.com
Example object, Pictor A
http://chandra.harvard.edu/photo/2016/pictora/
http://chandra.harvard.edu/photo/2016/pictora/pictora_xray.jpg
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)?

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.
Regards,
Martin Brown

[Moderator's note: Please send non-encoded short lines. Hit RETURN
after 70 characters if your software shows you line breaks but doesn't
send them. -P.H.]

Thanks and good point, time of flight, as the jets are million light year l=
ong, we would see the jet toward us first, and the jet away from us second,=
with perhaps 2 million years to who knows, 10 million years from jet emerg=
ence to our current view which could be anywhere along that entire evolutio=
n. The thing is, I've seen a lot of pictures, but it's always presented th=
at the hot spot is coming toward us.

My point is that there ought to be 50% of these objects where the hot spot =
we observe is the hot spot of the receding jet. I understand beaming and h=
ow we might not observe the receding jet vs the jet coming at us. But, the=
hot spot should be relatively stationary and glowing, so that we see both =
hot spots if there are two to be seen. And if they shut down so, we ought =
to see half of them with the receding hot spot and no observed jet because =
it is receding.

I don't recall seeing a hot spot without a jet feeding it such that the hot=
spot is supposed to be the receding hot spot, and no jet is observed due t=
o alignment. Is there an image of this out there that anyone knows?

rt

[Martin Brown]

Post by r***@gmail.com

Post by Martin Brown

Post by r***@gmail.com
Example object, Pictor A
http://chandra.harvard.edu/photo/2016/pictora/pictora_xray.jpg
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)?

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.

[Moderator's note: Please send non-encoded short lines. Hit RETURN
after 70 characters if your software shows you line breaks but doesn't
send them. -P.H.]

Its sometimes hard to know if your mail client is misbehaving this way.

Post by r***@gmail.com
Thanks and good point, time of flight, as the jets are million light year l=
ong, we would see the jet toward us first, and the jet away from us second,=
with perhaps 2 million years to who knows, 10 million years from jet emerg=
ence to our current view which could be anywhere along that entire evolutio=
n. The thing is, I've seen a lot of pictures, but it's always presented th=
at the hot spot is coming toward us.

The brightest one will be since we get the benefit of it being nearer,
geometrical line of sight into the beam and relativistic beaming. The
near hotspot we are looking directly at the impact shock front of the
relativistic beam into pristine IGM but on the far side we are looking
at the shock front through the backwash of material flowing away.

Post by r***@gmail.com
My point is that there ought to be 50% of these objects where the hot spot =
we observe is the hot spot of the receding jet. I understand beaming and h=
ow we might not observe the receding jet vs the jet coming at us. But, the=
hot spot should be relatively stationary and glowing, so that we see both =
hot spots if there are two to be seen. And if they shut down so, we ought =
to see half of them with the receding hot spot and no observed jet because =
it is receding.

It is fair to point out here that FRII are the most powerful radio
galaxies where the jets are way more potent than the IGM. OTOH FRI radio
galaxies have a puny jet strength compared to the IGM and look more like
terrestrial smoke stacks fighting against wind shear.

3C465 being a canonical nice bright well studied example:
http://www.jb.man.ac.uk/atlas/object/3C465.html

Or for an example 3C83.1 having a really bad hair day:
http://www.jb.man.ac.uk/atlas/object/3C83P1B.html

Post by r***@gmail.com
I don't recall seeing a hot spot without a jet feeding it such that the hot=
spot is supposed to be the receding hot spot, and no jet is observed due t=
o alignment. Is there an image of this out there that anyone knows?

3C16 is the closest I can think of where there is a huge asymmetry
between the brightness of the lobes and hotspots.

http://www.jb.man.ac.uk/atlas/object/3C16.html

You might want to look through the DRAGN catalogue at Jodrell Bank to
get a feel for what variable morphology of radio galaxies looks like:

http://www.jb.man.ac.uk/atlas/alpha.html

I'll also add the links for 3C84 and 3C303 with hotspots seen inside the
radio lobes that I forgot from a previous post:

http://www.jb.man.ac.uk/atlas/object/3C84.html

http://www.jb.man.ac.uk/atlas/object/3C303.html

Historical note for the OP.

Radio sources named Constellation A/B/C etc date from the birth of radio
astronomy and are big, very bright and well studied at many wavelengths
and resolutions.

Radio sources named 3Cnnn are from the third Cambridge catalogue (the
first truly reliable one that didn't overstate the numbers due to
sidelobe problems) and are again bright and amenable to detailed study
by modern instruments. Radio source numbers was a hot topic in the 60's
since it showed up another flaw in the Steady State theory. Namely that
looking back in time the early universe was a much more exciting place
than it is today (not at all good news for Steady State proponents).

[r***@gmail.com]

Thanks for the links and comments.

Question: Is there evidence that material (gas and or stars) is
"raining" back down onto galaxies where the radio jets appear to
be old and fading?

In other words, suppose FR I galaxies with intense jets observed
near the central engine are "young" and FR II galaxies with wider
opening angles are "older", meaning, it's been longer since the
initial launch of the radio jets.

then, objects with fading radio lobes, and no central jets, are
taken to be older still.

(does this classification fit what people think?.....and)

Is there any evidence for material (gas and or stars) raining back
down onto the galaxies? And if so, does it fit that the above
sequence holds, with the matter raining back down being most
associated with the "oldest" systems, ie, longest time since initial
jet launch?

In other words, if excess angular momentum is what gives rise to
the jets, then, shutting down that angular momentum would kill the
jets. If matter is ejected along the polar axis, and then that
material later rains down onto the galaxy, the angular momentum of
the "rain" would be orthogonal to the angular momentum of the jets,
thus, shutting down the jets.

Is this logic in keeping with consensus thinking?

Thanks,

Ross

[[Mod. note -- I am not an expert in this area, but (following the
standard model of jet production from accretion onto a supermassive
central black hole):
1. The angular momentum which gives rise to the jet would be that of
the accretion disk very close to the central supermassive BH (say
within no more than 100 Schwarzschild radia). The jets would come
out just about radially (along the BH's rotation axis, perpendicular
to the accretion disk), and so carry little net angular momentum.
(Recall that purely radial motion has zero angular momentum.)
2. I think jets usually start out going much faster than a galaxy's
(or even a galaxy cluster's) escape velocity. The jet then plows
into the interstellar medium in the galaxy, but I personally have
no idea of how much mass or linear/angular momentum ever returns
to the vicinity of the central BH. Is there enough to be a significant
influence on the accretion disk, magnetic field, or the BH's mass/spin?
Hopefully someone who knows the relevant modelling can provide
better-informed answers than my educated-guesses.
-- jt]]

[Martin Brown]

Post by r***@gmail.com
Thanks for the links and comments.
Question: Is there evidence that material (gas and or stars) is
"raining" back down onto galaxies where the radio jets appear to
be old and fading?

I shouldn't expect so. The momentum of the jet carries the shocked
material along with it away from the galaxy probably forever. There will
be some backwash but it won't have anything like the velocity to carry
it back to the core. Rough indications from the shapes of radio lobes in
powerful FR II sources are perhaps 1/3 the way back at most.

Post by r***@gmail.com
In other words, suppose FR I galaxies with intense jets observed
near the central engine are "young" and FR II galaxies with wider
opening angles are "older", meaning, it's been longer since the
initial launch of the radio jets.

There is a significant difference between the power of the central
engine in FR I and FR II galaxies with the latter being pretty much the
biggest and most powerful things in the universe. Whilst I would think
it possible that an FR I might sometimes evolve into an FR II by either
excessive feeding or BH merger. I don't think any would go the other
way. A discussion of their characteristics and modern interpretation is
online here:

https://ned.ipac.caltech.edu/level5/Glossary/Essay_fanaroff.html

Post by r***@gmail.com
then, objects with fading radio lobes, and no central jets, are
taken to be older still.
(does this classification fit what people think?.....and)
Is there any evidence for material (gas and or stars) raining back
down onto the galaxies? And if so, does it fit that the above
sequence holds, with the matter raining back down being most
associated with the "oldest" systems, ie, longest time since initial
jet launch?

I get the feeling you are thinking about the jets as fountains rather
than as astrophysical things. The backwash does fill up some of the void
punched out by the jet but I can't see if has much scope for raining
down onto the galaxy. It is way too tenuous for that.

One of the early incorrect models for double radio galaxies were that
the lobes were effectively plumes of less dense hot plasma rising
buoyantly in the intergalactic medium. Like hot air does on Earth.

Post by r***@gmail.com
In other words, if excess angular momentum is what gives rise to
the jets, then, shutting down that angular momentum would kill the
jets. If matter is ejected along the polar axis, and then that
material later rains down onto the galaxy, the angular momentum of
the "rain" would be orthogonal to the angular momentum of the jets,
thus, shutting down the jets.

It isn't excess angular momentum causing the jets it is the very fact
that the BH is spinning and magnetised. This provides a way to extract a
huge amount of rest mass energy out of infalling matter some of which
gets converted to jets escaping at the *poles* like aurora in reverse
but carrying away very little angular momentum compared with what is
being the input by the accretion disk. Arguably it may well be spinning
up a central BH by accretion of gas and stars at the centre of the
galaxy that spins them up to the point where the FRII relativistic jets
kick in. Prior to that FRI's only have jets with a roughly comparable
energy to the IGM and so get blown around more like smoke on Earth.

Post by r***@gmail.com
Is this logic in keeping with consensus thinking?

Not really. You are guessing and still haven't provided us with some
idea of where to pitch explanations.

Post by r***@gmail.com
[[Mod. note -- I am not an expert in this area, but (following the
standard model of jet production from accretion onto a supermassive
1. The angular momentum which gives rise to the jet would be that of
the accretion disk very close to the central supermassive BH (say
within no more than 100 Schwarzschild radia). The jets would come
out just about radially (along the BH's rotation axis, perpendicular
to the accretion disk), and so carry little net angular momentum.
(Recall that purely radial motion has zero angular momentum.)

One of the classic papers on jets is from 1979 Blandford & Konigl
https://ned.ipac.caltech.edu/level5/Glossary/Essay_fanaroff.html
(Blandford and Rees is behind a paywall for non-academic use)

Post by r***@gmail.com
2. I think jets usually start out going much faster than a galaxy's
(or even a galaxy cluster's) escape velocity. The jet then plows
into the interstellar medium in the galaxy, but I personally have
no idea of how much mass or linear/angular momentum ever returns
to the vicinity of the central BH. Is there enough to be a significant
influence on the accretion disk, magnetic field, or the BH's mass/spin?
Hopefully someone who knows the relevant modelling can provide
better-informed answers than my educated-guesses.
-- jt]]

I don't know for certain but my instinct is that once the radiation from
the central source really gets going its radiation pressure will expel
any gas and dust that isn't falling towards it in big chunks and quite
fast. This isn't a bad review for the OP with fewer equations:

https://arxiv.org/pdf/astro-ph/0301309v1.pdf

[r***@gmail.com]

Post by Martin Brown

Post by r***@gmail.com
Thanks for the links and comments.
Question: Is there evidence that material (gas and or stars) is
"raining" back down onto galaxies where the radio jets appear to
be old and fading?

Not really. You are guessing and still haven't provided us with some
idea of where to pitch explanations.

See Malin image at end of this post...........that's the stuff above the
galaxy that's observed for many galaxies. I'm looking for evidence that
stuff falls back inward and reduces the angular momentum of the material
and stars around the central BH system.

I forget the references (could look them up, but....), but I recall that
active galaxies with jets have excess angular momentum compared to
average.

So what I'm exploring and asking about, is the idea that a pair of
galaxies merge, the angular momentum of the stars is over time
communicated to the center. The massive black holes meanwhile move and
themselves merge....my idea I'm exploring is that this creates a bar of
stars, then the black holes slide down the bars and merge........see
wiki: https://en.wikipedia.org/wiki/Barred_spiral_galaxy

A dust lane is easy to see in many barred galaxies, and the dust lanes
are not aligned. They are offset and near center, curve into a circular
geometry. Imagine that's the ~path taken by the black holes which began
at the ends of the bar and created the bar, then after losing some
angular momentum, slid down the bar into the center and merged (or will
merge in cases where there still exists a pair of BH's observed)

(is there any observation where there is a bar in a galaxy, AND, there
are a pair of bright knots mid way to the center? ie, is there any
galaxy where there are perhaps two partial bars that don't connect on
center?)

That then creates excess angular momentum in the core after the BH's
have merged, and that then creates the jets. At least that's the idea
I'm exploring.

If true, then the only galaxies that should have jets are those where
there is excess angular momentum near the central black holes. The
question the n is, do the radio jets carry matter and or stars with
them?

Easy answer, no, but, see:

David Malin ultra deep image of Centaurus A showing faint stellar
extension s aligned with galactic radio jets (google search images,
"david malin, deep image, centaurus A" if link doesn't work:

https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd
=&cad=rja&uact=8&ved
hUKEwie4q-Ro5_SAhUCyWMKHRfuClkQjRwIBw&url=
http%3A%2F%2Fwww.pbase.com%2Fimage%2F110608746&psigQjCNHhArY_rn55WQOZp
Sdxzgu6_6ah0g&ust=1487700691719675

There is something that is out along the line of the jets (gas, stars,
both?). And IF matter were to rain back down onto a system with
increased angular momentum, the "rain" would be perpendicular to the
angular momentum of the initial system, thus reducing the angular
momentum............transforming a spiral into an elliptical (or
increasing the size of a central bulge).

Thoughts?

rt

[Martin Brown]

Post by r***@gmail.com

Post by Martin Brown

Post by r***@gmail.com
Thanks for the links and comments.
Question: Is there evidence that material (gas and or stars) is
"raining" back down onto galaxies where the radio jets appear to
be old and fading?

Not really. You are guessing and still haven't provided us with some
idea of where to pitch explanations.

See Malin image at end of this post...........that's the stuff above the
galaxy that's observed for many galaxies. I'm looking for evidence that
stuff falls back inward and reduces the angular momentum of the material
and stars around the central BH system.
I forget the references (could look them up, but....), but I recall that
active galaxies with jets have excess angular momentum compared to
average.

The reason that a black hole spins up is that it is very compact just
like a ballet dancer spins up when they bring their arms in. The stars
and other infalling matter in the accretion disk brings in ever more
angular momentum with it and that has to be conserved.

It would be as well to study the standard explanation of how Centaurus A
looks like it does before concocting a new explanation.

http://chandra.harvard.edu/photo/2002/0157/

Fairly serious shockwave through it around 10My ago is the favourite.

Post by r***@gmail.com
So what I'm exploring and asking about, is the idea that a pair of
galaxies merge, the angular momentum of the stars is over time
communicated to the center. The massive black holes meanwhile move and
themselves merge....my idea I'm exploring is that this creates a bar of
stars, then the black holes slide down the bars and merge........see
wiki: https://en.wikipedia.org/wiki/Barred_spiral_galaxy
A dust lane is easy to see in many barred galaxies, and the dust lanes
are not aligned. They are offset and near center, curve into a circular
geometry. Imagine that's the ~path taken by the black holes which began
at the ends of the bar and created the bar, then after losing some
angular momentum, slid down the bar into the center and merged (or will
merge in cases where there still exists a pair of BH's observed)

The general theory is that as galaxies age they mature towards having a
barred spiral structure through perturbations of the stellar orbits in
the galactic gravitational potential. See for example:

https://www.nasa.gov/mission_pages/hubble/science/bar_galaxies.html
http://hubblesite.org/hubble_discoveries/science_year_in_review/pdf/2008/barred_spiral_galaxies_and_galactic_evolution.pdf

The same happens in numerical simulations of stars in galaxies.

Post by r***@gmail.com
(is there any observation where there is a bar in a galaxy, AND, there
are a pair of bright knots mid way to the center? ie, is there any
galaxy where there are perhaps two partial bars that don't connect on
center?)
That then creates excess angular momentum in the core after the BH's
have merged, and that then creates the jets. At least that's the idea
I'm exploring.
If true, then the only galaxies that should have jets are those where
there is excess angular momentum near the central black holes. The
question the n is, do the radio jets carry matter and or stars with
them?

The jets will surely entrain a small cylinder of material with them but
they won't do much to a star or gas cloud beyond a quick bright flash
(and slowing it down for a while) - especially since the motion of a
star would not leave it in the jet for very long. Scheuer's denist's
drill model of jets still fits the observations pretty well.

http://mnras.oxfordjournals.org/content/370/3/1513.full.pdf

Post by r***@gmail.com
David Malin ultra deep image of Centaurus A showing faint stellar
extension s aligned with galactic radio jets (google search images,
https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd
=&cad=rja&uact=8&ved
hUKEwie4q-Ro5_SAhUCyWMKHRfuClkQjRwIBw&url=
http%3A%2F%2Fwww.pbase.com%2Fimage%2F110608746&psigQjCNHhArY_rn55WQOZp
Sdxzgu6_6ah0g&ust=1487700691719675
There is something that is out along the line of the jets (gas, stars,
both?). And IF matter were to rain back down onto a system with
increased angular momentum, the "rain" would be perpendicular to the
angular momentum of the initial system, thus reducing the angular
momentum............transforming a spiral into an elliptical (or
increasing the size of a central bulge).

You clearly don't understand angular momentum so this is going nowhere.

You would have to drop serious amounts of matter in a retrograde orbit
into a black hole to appreciably alter its huge angular momentum. Whilst
I am inclined to never say never I am pretty sure that it would require
incredibly exceptional circumstances for this to happen in a real galaxy
system.

A retrograde orbit BH merger would be about the only thing that might.

[r***@foothillelectric.net]

On Thursday, February 23, 2017 at 7:47:09 AM UTC-8, Martin Brown

Post by Martin Brown
The general theory is that as galaxies age they mature towards having a
barred spiral structure through perturbations of the stellar orbits in
https://www.nasa.gov/mission_pages/hubble/science/bar_galaxies.html
http://hubblesite.org/hubble_discoveries/science_year_in_review/pdf/2008/barred_spiral_galaxies_and_galactic_evolution.pdf
The same happens in numerical simulations of stars in galaxies.

Nice images, some of my favorite galaxies.

The sequence for bar evolution seems backwards to me (counter to
entropy which wants to randomize things....globular clusters and
ellipticals seem to me to be the end stage of evolution).

The formation of a bar also seems counter to Rubin observation that
the circular velocity is constant with radius.......the larger
circular orbit would inevitably sweep the arms into a spiral.

This is more the sequence that I'm studying / seeking evidence for:



1) Mice Loading Image...

2) Fornax Loading Image...


3) ngc1097 https://en.wikipedia.org/wiki/NGC_1097

4) ngc1232 Loading Image...

This is about opposite the sequence at the Hubblesite link you sent.

Basics:

The net angular momentum of a globular cluster of stars is zero,
right?

Same for an elliptical (generally and ignoring the possible small
rotation component some have).

In contrast, spirals have large angular momentum in their outer
disk stars, vs (much? near zero) smaller angular momentum in their
central bulges of stars.

As suggested, To merge a counter rotating galaxy is a way to zero
out the angular momentum. That's not what I'm suggesting.

If you instead add angular momentum that is orthogonal, then you
randomize the stellar orbits. This is what we see in ellipticals
and globulars.

The angular momentum of matter raining down along an approximately
axial line (ie, in a highly elliptical orbital geometry, with the
long axis of the ellipse being the rotation axis of the galaxy.
Then, the axis of rotation for the galaxy is orthogonal to the axis
of rotation for the ellipse of in falling material.

As this "rain" component becomes "thermalized" by interacting with
the mass of the galaxy, some of the disk stars orbits are transformed
into elliptical orbits. In this way, a spiral galaxy could evolve
to become an elliptical galaxy.

And it all began from the BH that ejected matter along the axis of
too much angular momentum. Each episode of activity, increasing
the size of the bulge, until eventually the galaxy is an elliptical
and the stars can age from there............(ellipticals have older
stars)

I'm not talking (primarily) about BH angular momentum here, I'm
talking about galactic angular momentum.

BUT, over time, whatever angular momentum the galaxy has winds up
being communicated throughout the system and right into the center
where it then tells the BH what angular momentum it must adopt
because it's angular momentum results from the stuff falling into
it, and not the other way round..............

In this model, an active BH happens when an excess of angular
momentum is communicated into the BH environment. It ejects material,
the material rains down, interacts and randomizes angular momentum
of the galaxy, the BH goes dormant and the spiral nature evolves
toward elliptical.

Post by Martin Brown
You would have to drop serious amounts of matter in a retrograde orbit

Serious amounts of matter............yes

retrograde orbit.............no.

It needs to cancel out or randomize, the existing angular momentum.
See above.


rt

[r***@gmail.com]

I should mention, regarding the rain idea I'm studying, that if matter is s=
hot out of a galaxy along the axis of rotation by BH jet activity, and it s=
ubsequenty "rain's" back down onto the galaxy, the NET angular momentum of=
the "rain" would also be zero. It would also be orthogonal to (have angul=
ar momentum vector orthogonal to) the angular momentum of the galaxy.

Thus, rain if it exists, will reduce net angular momentum of a galaxy, shut=
ting down rotation and evolving the galaxy from spiral forms toward EO.

This is possible if the individual particles, stars, gas, dust, rain back d=
own along highly elliptical geometries with long axis coincident with galac=
tic rotation vector, AND, the rain is random with regards to which side of =
the central black hole it falls on. This way, the momentum vectors for eac=
h "particle" are roughly within the disk of the galaxy's rotation, ~normal =
to it's angular rotation vector. But the vector for each particle is diffe=
rent so that there is no net rotation axis.

In a sense, the rain would probably be a bit like a faint bar of stuff that=
thermalization would randomize......the rain would become random like orbi=
ts in a GC, and, the matter of the galaxy with which the interaction took p=
lace would also become more random, more like an elliptical.

So, BH jets, are observed to eject matter. **IF** that matter rains back d=
own, then it should act to evolve the galaxy toward elliptical by some degr=
ee. More rain, more evolution.

Question is, can any observation detect such a rain IF it exists? We see f=
aint extensions. But finding their velocity is harder still and I don't kn=
ow of any observation for the velocity of the faint extended material along=
BH jet axis'.

This mechanism is why the EO to Bar evolution path makes no sense to me. T=
here are only old stars in ellipticals. Barred spirals have newborn stars.=
And most galaxies observed are ellipticals, and they have only old stars.=
EO ought to be the end game it seems to me.

Is it the general expectation that all elliptical galaxies will evolve to b=
arred spirals eventually?

rt

[Steve Willner]

Post by r***@gmail.com
Is it the general expectation that all elliptical galaxies will
evolve to barred spirals eventually?

No. Most, maybe all, galaxies evolve to ellipticals. There is great
debate about the mechanism and the timing of this evolution, but
observations show greater fractions of ellipticals at later cosmic
times. One paper I happen to be familiar with is at
http://adsabs.harvard.edu/abs/2015ApJ...803...26P

I especially like Figs 12 and 13 (and had nothing at all to do with
making them other than helping provide some of the data).

[Martin Brown]

Post by r***@foothillelectric.net
On Thursday, February 23, 2017 at 7:47:09 AM UTC-8, Martin Brown

Post by Martin Brown
The general theory is that as galaxies age they mature towards having a
barred spiral structure through perturbations of the stellar orbits in
https://www.nasa.gov/mission_pages/hubble/science/bar_galaxies.html
http://hubblesite.org/hubble_discoveries/science_year_in_review/pdf/2008/barred_spiral_galaxies_and_galactic_evolution.pdf
The same happens in numerical simulations of stars in galaxies.

Nice images, some of my favorite galaxies.
The sequence for bar evolution seems backwards to me (counter to
entropy which wants to randomize things....globular clusters and
ellipticals seem to me to be the end stage of evolution).

Entropy doesn't mean what you think it means.

When a galaxy is formed the original conditions determine how much total
angular momentum it inherits from the gas cloud that it formed from. The
ratio of mass to angular momentum influences what it looks like and at a
certain amount of angular momentum spontaneous symmetry breaking occurs
and the whole thing looks much more complicated.

Q Is it known at what ratio of mass to angular momentum a forming galaxy
necessarily becomes a spiral rather than elliptical?

Here is one paper I found which tries to address the problem
semianalytically. I found another but lost the link. Perhaps someone can
suggest a better review of the morphology and secular of galaxies in
relation to their instrinsic angular momentum.

https://arxiv.org/pdf/1605.00647.pdf

Post by r***@foothillelectric.net
The formation of a bar also seems counter to Rubin observation that
the circular velocity is constant with radius.......the larger
circular orbit would inevitably sweep the arms into a spiral.

ISTR that in the early days of large scale galactic simulations they had
to work very hard to prevent bars from falling. I suspect bars and
ellipticals represent a galactic manifestation of Ovenden's conjecture
that stellar systems evolve towards configurations where the stars keep
their distance from each other as far is possible.

Post by r***@foothillelectric.net
1) Mice https://en.wikipedia.org/wiki/Mice_Galaxies#/media/File:Merging_galaxies_NGC_4676_(captured_by_the_Hubble_Space_Telescope).jpg
2) Fornax https://en.wikipedia.org/wiki/Barred_spiral_galaxy#/media/File:Phot-08a-99-hires.jpg
3) ngc1097 https://en.wikipedia.org/wiki/NGC_1097
4) ngc1232 https://en.wikipedia.org/wiki/NGC_1232#/media/File:NGC1232B.jpg
This is about opposite the sequence at the Hubblesite link you sent.
The net angular momentum of a globular cluster of stars is zero,
right?

Certainly small angular momentum.

And slowly getting smaller by expelling the odd star to infinity and the
remainder becoming ever more tightly gravitationally bound.

Post by r***@foothillelectric.net
Same for an elliptical (generally and ignoring the possible small
rotation component some have).
In contrast, spirals have large angular momentum in their outer
disk stars, vs (much? near zero) smaller angular momentum in their
central bulges of stars.

That is because angular momentum scales as Mr^2

Post by r***@foothillelectric.net
As suggested, To merge a counter rotating galaxy is a way to zero
out the angular momentum. That's not what I'm suggesting.

But that is the only thing that will work (or a galaxy with same spin
whose orbit is retrograde to the first and with goldilocks conditions to
null out the total angular momentum). Angular momentum is a *vector*
quantity you have to add an equal and opposite amount to null it out.

Post by r***@foothillelectric.net
If you instead add angular momentum that is orthogonal, then you
randomize the stellar orbits. This is what we see in ellipticals
and globulars.

Nonsense. If you added an orthogonal amount of angular momentum to
original galaxy one with W1 = (I, 0, 0) and add W2 = (0, I, 0)

You get a new merged galaxy with WTot = (I, I, 0)

In other words sqrt(2).I and at 45 degrees to the original spin axis.

Post by r***@foothillelectric.net
The angular momentum of matter raining down along an approximately
axial line (ie, in a highly elliptical orbital geometry, with the
long axis of the ellipse being the rotation axis of the galaxy.
Then, the axis of rotation for the galaxy is orthogonal to the axis
of rotation for the ellipse of in falling material.

You really do not understand the basics of Newtonian dynamics.

Post by r***@foothillelectric.net
As this "rain" component becomes "thermalized" by interacting with
the mass of the galaxy, some of the disk stars orbits are transformed
into elliptical orbits. In this way, a spiral galaxy could evolve
to become an elliptical galaxy.

Angular moment is one of the key invariants that is conserved in an
isolated system - and that remains true even in the full GR treatment.

Post by r***@foothillelectric.net
And it all began from the BH that ejected matter along the axis of
too much angular momentum. Each episode of activity, increasing
the size of the bulge, until eventually the galaxy is an elliptical
and the stars can age from there............(ellipticals have older
stars)

It doesn't work like that.

Post by r***@foothillelectric.net

Post by Martin Brown
You would have to drop serious amounts of matter in a retrograde orbit

Serious amounts of matter............yes

But the angular momentum would remain the *same* the galaxy might spin
more slowly as it became more massive since the same angular momentum
would be shared by a larger total mass

Post by r***@foothillelectric.net
retrograde orbit.............no.
It needs to cancel out or randomize, the existing angular momentum.
See above.

Sorry but you do not have a clue.

[r***@gmail.com]

Post by r***@foothillelectric.net
On Thursday, February 23, 2017 at 7:47:09 AM UTC-8, Martin Brown
If you instead add angular momentum that is orthogonal, then you
randomize the stellar orbits. This is what we see in ellipticals
and globulars.

Nonsense. If you added an orthogonal amount of angular momentum to=20
original galaxy one with W1 = (I, 0, 0) and add W2 = (0, I, 0)
You get a new merged galaxy with WTot = (I, I, 0)
In other words sqrt(2).I and at 45 degrees to the original spin axis.
Regards,
Martin Brown

OK, fine, yes I understand and see that result. But you are
considering just one infalling object and it's single interaction
with a single entity of the original galaxy.

Suppose I have a spiral galaxy, disk with central bulge. We can
find the net angular momentum.

Now, thought experiment, I take a bunch of mass, call it a bunch
of stars and I place them far above the spiral galaxy, say 100,000
to 200,000 light years from the black hole, in a clump along the
axis of rotation of the spiral galaxy. Then, I allow all of these
stars to rain down onto the spiral galaxy. They fall on random
sides of the black hole, and have random elliptical motions with a
very large eccentricity..........long axis parallel to the spiral
axis of rotation.

Suppose the total mass of this infalling material is significant
in comparison to, but smaller than, the mass of the spiral galaxy.

For each in falling thought experiment star, that interacts with a
star of the spiral, the net angular momentum will become as you
say, at a 45 degree angle. =20

HOWEVER, some of the in falling stars have a 45 degree angle one
way, and others have a 45 degree angle in another orientation. And,
as the falling stars manage to fall all around the black hole like
rain drops, the net angular momentum for each of these infalling
stars is in a different direction. Further, some are falling from
North pole down onto the galaxy, others are falling from the South
pole up into the galaxy, further increasing the random nature of
the resultant stellar motions.

Take those, and then secondary and tertiary further interactions
with the spiral galaxy stars, and the total motions become randomized
and the galactic net angular momentum will be reduced..........right?

Now I don't know that it is known what the faint extensions of
active galaxies are (gas, dust, stars, ????.........e.g. David
Malin's unsharp masking method for bringing out faint details for
these objects, showing extensions coincident with radio jet directions
for several active galaxies....

So I don't know that the extensions are stars (does anyone?)

But no matter what, if the total mass is significant and if that
mass rains back down, it still seems to me that it should reduce
the net angular momentum of the spiral.

rt

[Martin Brown]

Post by r***@gmail.com

Post by Martin Brown

Post by r***@foothillelectric.net
On Thursday, February 23, 2017 at 7:47:09 AM UTC-8, Martin Brown
If you instead add angular momentum that is orthogonal, then you
randomize the stellar orbits. This is what we see in ellipticals
and globulars.

Nonsense. If you added an orthogonal amount of angular momentum to
original galaxy one with W1 = (I, 0, 0) and add W2 = (0, I, 0)
You get a new merged galaxy with WTot = (I, I, 0)
In other words sqrt(2).I and at 45 degrees to the original spin axis.

OK, fine, yes I understand and see that result. But you are
considering just one infalling object and it's single interaction
with a single entity of the original galaxy.

It works just the same for many infalling objects too. Angular momentum
is conserved in an isolated dynamical system if there is no friction.

Post by r***@gmail.com
Suppose I have a spiral galaxy, disk with central bulge. We can
find the net angular momentum.
Now, thought experiment, I take a bunch of mass, call it a bunch
of stars and I place them far above the spiral galaxy, say 100,000
to 200,000 light years from the black hole, in a clump along the
axis of rotation of the spiral galaxy. Then, I allow all of these
stars to rain down onto the spiral galaxy. They fall on random
sides of the black hole, and have random elliptical motions with a
very large eccentricity..........long axis parallel to the spiral
axis of rotation.
Suppose the total mass of this infalling material is significant
in comparison to, but smaller than, the mass of the spiral galaxy.

OK. Simple example to try and make the distinction between angular
momentum and angular velocity. Lets say we have a slab of material with
zero angular momentum that we somehow stitch onto the original galaxy
instantly and that they have the same mass M1 = M2 = M.

W1 = (I, 0, 0) and W2 = (0, 0, 0) Wtot = W1= (I, 0, 0) Mtot = 2M

The angular velocity has been halved by this process since the new
galaxy has the same angular momentum as before but is now mass 2M.

Post by r***@gmail.com
But no matter what, if the total mass is significant and if that
mass rains back down, it still seems to me that it should reduce
the net angular momentum of the spiral.

Only because you don't understand basic Newtonian physics.

[r***@gmail.com]

OK, decades since I've crunched some of these equations, so thanks for
the refresher.

How about this example:

at (0,0,0) I have a SMBH at the center of a galaxy.

The galaxy is purely a disk of stars in the XY plane, with rotation
about the Z axis. Right hand rule, thumb North, fingers show stellar
rotation direction. Disk is thin, call it 1pc compared to 50kpc radius
for the disk.

Now, I drop a bunch of stars from N and S of the SMBH. They fall onto
different sides of the SMBH, AND, they thermalize with the disk stars.

Seems to me I will form a central bulge where initially none existed.

From your comments (which make sense), the net angular momentum of the
system will not change. But where I'm still confused, is how the sum of
angular momentum of the in falling material, adds to the disk rotation
angular momentum.

for the disk material, the angular momentum vector is in the north Z
direction. For the infalling material, the angular momentum vector for
each in falling star is in the XY plane, orthogonal to the disk
material.

As the infalling material "thermalizes" with the disk stars, a central
bulge will form with random motions..........but I am not sure how the
Net becomes changed or if it does.

If the infalling material falls in equally on all sides of the central
SMBH, then, it must have zero angular momentum. Therefore by your
comments, (which make sense) the resultant bulge must have a net angular
momentum that's still along the Z axis north.

right?

rt

[j***@gmail.com]

@ross.t: there's a citizen science (crowd sourcing) project which
is very much related to your questions, in a general sense, Radio
Galaxy Zoo.
Main page: https://radio.galaxyzoo.org/#/
Discussion forum: https://radiotalk.galaxyzoo.org/

To repeat what's already been said, to be visible as radio
lobes/hotspots/jets/etc, the back-to-back relativistic jets created
near the SMBH in the nucleus have to get through, and be seen
through, first the ISM of the galaxy, then the IGM between galaxies.
It's nice if both are homogeneous, but often they aren't. And there's
relative motion too, producing such things as 'narrow angle tails'
and 'wide angle tails'.

On timescales: there's a class of radio sources called "giants",
lobe-to-lobe distances as great as 5 Mpc. There are also some which
are "restarted", in at least one case, at least three times.=20

On single vs double jets, there's a rare class of object called
"hybrid" or "HyMoRS" (Hybrid Morphology Radio Sources), where the
radio morphology of one side (jet/lobe) is extremely different from
that of the other.