APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec 05)

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Expand view Topic review: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec 05)

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by jacksmom60 » Thu Dec 05, 2013 4:06 am

Horus wrote:Hi guys, is it me or do those jets look like they are turning counter clockwise? The jet on the left coming towards us and the right one travelling away.
I agree with you on this....I see the same thing. They do look as though they are turning counter clockwise with the one on the left coming forward and the right moving away.

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by Nitpicker » Wed Dec 04, 2013 11:59 pm

neufer wrote:
Nitpicker wrote:
But with my 6" SCT (1500mm/10) at prime focus on my DSLR, with a high ISO 6400 setting,
I need a good 30 seconds of exposure to convincingly detect a point source of vmag 15.
http://www.universetoday.com/106932/a-naked-eye-nova-erupts-in-centaurus/#more-106932 wrote:
A Naked Eye Nova Erupts in Centaurus
by David Dickinson, Universe Today, December 4, 2013

<<If you live in the southern hemisphere, the southern sky constellation of Centaurus may look a little different to you tonight, as a bright nova has been identified in the region early this week.
Image
An animation showing a comparison between the constellation Centaurus before and after a nova eruption. Credit and copyright: Ernesto Guido, Nick Howes and Martino Nicolini/Remanzacco Observatory. :arrow:

The initial discovery of Nova Centauri 2013 (Nova Cen 2013) was made by observer John Seach based out of Chatsworth Island in New South Wales Australia. The preliminary discovery magnitude for Nova Cen 2013 was magnitude +5.5, just above naked eye visibility from a good dark sky site. Estimates by observers over the past 24 hours place Nova Cen 2013 between magnitudes +4 and +5 “with a bullet,” meaning this one may get brighter still as the week progresses.>>
Thanks neufer. Currently, looks like I'd be able to observe Nova Cen 2013 between about 2 and 4am from here. Hmmm, I might look at the photos I took of Nova Del 2013 earlier this year, and go to bed early instead. :ssmile:

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by Nitpicker » Wed Dec 04, 2013 11:50 pm

Chris Peterson wrote: Okay. I'll note there is a substantial difference between that clarification and your original statement, " I cannot convincingly detect a point source dimmer than vmag 15."
Quite right Chris. I now wish I had never mentioned my own case, as I am limited to subs of ~30s due to field rotation, due to my (poor) choice of alt-az mount for (not very) deep sky photography. Initially, I thought that by setting the ISO so high, I was bringing the image to the limit of sky glow faster. I now know (thanks mainly to the education you've given me over the last couple of months) that while I am detecting more objects this way, I am also increasing the readout noise and reducing the S/N ratio. I'm probably still a fair way from the limit of my sky glow.

My original point -- however poorly expressed originally -- was that very few amateur deep sky photographers, shooting through the atmosphere, seem to produce narrow-field images, no doubt due to the extra time and money it requires. It is hard to compete with technology like the HST.

It would have been better if my original statement said something like "the vast majority of amateurs would struggle to produce a satisfactory narrow-field image of Hercules A (or more interesting targets comparable in apparent size and magnitude)". This is slightly different from Roger's implication (as I perceived it) that amateurs leave objects like this alone because they can only achieve wide-field images.
Chris Peterson wrote: Aesthetically, we tend to like high surface brightness images, which means you'll need a longer exposure time. But the same information is present in the shorter exposure image made at a long focal length.
I take your point, but if my eyes can't detect an object in an image, I would argue (perhaps semantically) it is more than just a lack of aesthetics. I assume you mean that "the same information is present in the shorter exposure image made at a long focal length" [or short focal length].

...

My original point could just as easily have not been made, as it wasn't a particularly important point. But I'm glad I made it, and that I had the opportunity to clarify it, because it opened up a sideline of discussion from which I have learnt a few things. Many thanks.

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by neufer » Wed Dec 04, 2013 10:52 pm

Nitpicker wrote:
But with my 6" SCT (1500mm/10) at prime focus on my DSLR, with a high ISO 6400 setting,
I need a good 30 seconds of exposure to convincingly detect a point source of vmag 15.
http://www.universetoday.com/106932/a-naked-eye-nova-erupts-in-centaurus/#more-106932 wrote:
A Naked Eye Nova Erupts in Centaurus
by David Dickinson, Universe Today, December 4, 2013

<<If you live in the southern hemisphere, the southern sky constellation of Centaurus may look a little different to you tonight, as a bright nova has been identified in the region early this week.
Image
An animation showing a comparison between the constellation Centaurus before and after a nova eruption. Credit and copyright: Ernesto Guido, Nick Howes and Martino Nicolini/Remanzacco Observatory. :arrow:

The initial discovery of Nova Centauri 2013 (Nova Cen 2013) was made by observer John Seach based out of Chatsworth Island in New South Wales Australia. The preliminary discovery magnitude for Nova Cen 2013 was magnitude +5.5, just above naked eye visibility from a good dark sky site. Estimates by observers over the past 24 hours place Nova Cen 2013 between magnitudes +4 and +5 “with a bullet,” meaning this one may get brighter still as the week progresses.>>

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by Chris Peterson » Wed Dec 04, 2013 3:00 pm

Nitpicker wrote:But with my 6" SCT (1500mm/10) at prime focus on my DSLR, with a high ISO 6400 setting, I need a good 30 seconds of exposure to convincingly detect a point source of vmag 15. As you say, aperture is what matters.
Okay. I'll note there is a substantial difference between that clarification and your original statement, " I cannot convincingly detect a point source dimmer than vmag 15."
My understanding of slowing down the focal ratio (via eyepiece projection, say) is that you reduce the FOV, thereby spreading the desired target across more pixels, so each pixel gets less photons per unit time. So a slower focal ratio requires a longer exposure.
For a long exposure, the S/N is determined primarily by the number of photons collected, which is a function of the aperture and exposure time. With a slower focal ratio, each pixel sees fewer electrons, and therefore has higher noise, but the object as a whole doesn't have more noise than you'd have if you used the same scope at a shorter focal length. You can test this quite easily by just shrinking the image digitally to what you'd have with the faster scope. Aesthetically, we tend to like high surface brightness images, which means you'll need a longer exposure time. But the same information is present in the shorter exposure image made at a long focal length.

This is why the best imaging strategy is to select your focal length based on the camera you are using, and then go for as much aperture as you can afford.
Also, based only on my experience in the field, I have simply concluded that a diffuse object like a galaxy or nebula is always more difficult to detect than a point source of the same vmag.
Visually, that is certainly true. Our eyes aren't pure photon counters- they respond to surface brightness as well.

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by Nitpicker » Wed Dec 04, 2013 6:27 am

Chris Peterson wrote:
Nitpicker wrote:But at vmag 17.8, which is at least 5 orders dimmer than anything in the Messier and Caldwell catalogues (and spread out over its apparent size) it would definitely be a struggle to detect. Besides, elliptical galaxies aren't the pretty ones anyway. You can take overexposed photos of the Moon or Venus and obtain results that look like elliptical galaxies. Trust me, I know. :ssmile:

I have a modest SCT scope (1500mm FL, f/10) and a DSLR capable at high ISO, and fairly dark, but still suburban skies, and I cannot convincingly detect a point source dimmer than vmag 15. It is even more difficult when I slow down the focal ratio beyond prime focus to reduce the FOV, as I do when imaging planets.
That seems curious. With my 12" SCT here, I can easily image small, mag 18 extended objects with a few minute exposure. Even when I lived in the middle of Southern California light pollution, I only needed 10 seconds to capture the Ring Nebula, including its mag 15 central star, with an 8" SCT.

Certainly, a DSLR isn't ideal for astronomical imaging, but it isn't that bad! Also, aperture is what matters. Focal ratio has no impact on sensitivity except for very short exposures, where readout noise dominates.
I'm certainly not saying my technique is optimised. I'm sure I could squeeze a bit more out of my scope, but the law of diminishing returns tends to make me lazy. I've been reluctant to get into image stacking and processing in any serious way -- I probably need to address that.

But with my 6" SCT (1500mm/10) at prime focus on my DSLR, with a high ISO 6400 setting, I need a good 30 seconds of exposure to convincingly detect a point source of vmag 15. As you say, aperture is what matters.

My understanding of slowing down the focal ratio (via eyepiece projection, say) is that you reduce the FOV, thereby spreading the desired target across more pixels, so each pixel gets less photons per unit time. So a slower focal ratio requires a longer exposure. Happy to be corrected here. I always appreciate your comments, Chris.

Also, based only on my experience in the field, I have simply concluded that a diffuse object like a galaxy or nebula is always more difficult to detect than a point source of the same vmag.

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by Chris Peterson » Wed Dec 04, 2013 5:46 am

Nitpicker wrote:But at vmag 17.8, which is at least 5 orders dimmer than anything in the Messier and Caldwell catalogues (and spread out over its apparent size) it would definitely be a struggle to detect. Besides, elliptical galaxies aren't the pretty ones anyway. You can take overexposed photos of the Moon or Venus and obtain results that look like elliptical galaxies. Trust me, I know. :ssmile:

I have a modest SCT scope (1500mm FL, f/10) and a DSLR capable at high ISO, and fairly dark, but still suburban skies, and I cannot convincingly detect a point source dimmer than vmag 15. It is even more difficult when I slow down the focal ratio beyond prime focus to reduce the FOV, as I do when imaging planets.
That seems curious. With my 12" SCT here, I can easily image small, mag 18 extended objects with a few minute exposure. Even when I lived in the middle of Southern California light pollution, I only needed 10 seconds to capture the Ring Nebula, including its mag 15 central star, with an 8" SCT.

Certainly, a DSLR isn't ideal for astronomical imaging, but it isn't that bad! Also, aperture is what matters. Focal ratio has no impact on sensitivity except for very short exposures, where readout noise dominates.

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by geckzilla » Wed Dec 04, 2013 3:43 am

Beings in elliptical galaxies probably have a lot clearer view of the cosmos without all that dust, though. I wonder if they are full of planetary nebulas, as well?

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by Nitpicker » Wed Dec 04, 2013 2:53 am

Roger wrote:The galaxy is also known as PGC 59117, and is of visual magnitude 17.8. It appears to be the largest galaxy in a dense cluster. Although this is within reach of amateur astrophotographers, it would be tiny on their CCD chips, so most amateurs leave such distant objects alone. So, the Hubble view is shown. (Of course, the radio jets would not show up in CCD images.)
According to this image: the optical signal of Hercules A would appear with roughly the same angular size as many of the Solar System planets routinely photographed by amateurs. But at vmag 17.8, which is at least 5 orders dimmer than anything in the Messier and Caldwell catalogues (and spread out over its apparent size) it would definitely be a struggle to detect. Besides, elliptical galaxies aren't the pretty ones anyway. You can take overexposed photos of the Moon or Venus and obtain results that look like elliptical galaxies. Trust me, I know. :ssmile:

I have a modest SCT scope (1500mm FL, f/10) and a DSLR capable at high ISO, and fairly dark, but still suburban skies, and I cannot convincingly detect a point source dimmer than vmag 15. It is even more difficult when I slow down the focal ratio beyond prime focus to reduce the FOV, as I do when imaging planets.

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by Roger » Tue Dec 03, 2013 11:15 pm

The galaxy is also known as PGC 59117, and is of visual magnitude 17.8. It appears to be the largest galaxy in a dense cluster. Although this is within reach of amateur astrophotographers, it would be tiny on their CCD chips, so most amateurs leave such distant objects alone. So, the Hubble view is shown. (Of course, the radio jets would not show up in CCD images.)

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by Spif » Thu Dec 06, 2012 11:23 pm

BMAONE23 wrote:It would seem to me that to have a "Wobble" motion to the BH rotation
I've never heard of black holes (really, their magnetic fields) precessing. All of the active nuclei examples I've seen have been stable straight jets with sizes on the order of 1M light years, implying that they are rock steady for long periods of time. But my Astrophysics is undergrad and was from 20 years ago, so take counter point with a grain of salt.
or even a Toroid shape encircling the "Equatorial" region of the BH implies that the beast must have a measurable size to allow for an equatiroal region to exist.
I think references to "equatorial" regions are usually in reference to the zone away from the poles where the jets flow out. The accretion disk (not part of the black hole) tends to align with the equatorial spin I think. And then outside of that there is a ring of dust that usually obscures the fun part of the accretion disk where the black hole ingests matter.

Black holes and their event horizons I think are always very close to spherical. But I've seen an animation of a model of merging black holes where they were expected to become squat ellisoids. Perhaps that squishing of the shape might be a function of space time distortions around the extreme gravity between the black holes and perhaps the model does not necessarily require there to be a finite shape or structure within the event horizon?

-s

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by Spif » Thu Dec 06, 2012 11:08 pm

Alfred wrote: There is a factor 1000 mentioned with regards to the size of the central black hole and the size of the Galaxy... Is there any evidence to suggest that big black holes reside in big galaxies, and vice versa? I assume Our sun would be racing at great speeds becauce of the gravity from the black hole monster?
Yes, up until recently, it has been generally found that there is an apparent correlation between galaxy mass and the mass of the central black hole. However, a paper just came out that found an extreme distance (very early) small galaxy with a disproportionately large central black hole. This surprises and disturbs galactic evolution astronomers... is it a weird anomaly or is there something very wrong with our assumptions of how galaxies and central black holes evolve? We don't know yet... so now they're on the hunt for more of these cases.

But as I understand it, in terms of recent (nearby) galaxies, there is generally a correlation.

-s

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by Greg Hilton » Thu Dec 06, 2012 9:20 pm

If each jet is 1M light years in size, then the whole structure is roughly 2M light years across. It would seem like this makes it one of the largest coherent structures in the universe. Is this true? (Even though they are gravitationally bound, I would not classify galactic clusters or superclusters as coherent structures. Colliding/merging galaxies, yes.)

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by BMAONE23 » Thu Dec 06, 2012 8:21 pm

It would seem to me that to have a "Wobble" motion to the BH rotation, or even a Toroid shape encircling the "Equatorial" region of the BH implies that the beast must have a measurable size to allow for an equatiroal region to exist. Then to have Polar jet features might further imply the existance of dipolar magnetism. If this were a true singularity it would almost certainly need to be monopolar. This would suggest that BH's, within the Event Horizon, have both mass and measurable size and aren't singularities.

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by neufer » Thu Dec 06, 2012 6:44 pm

Alfred wrote:
What sort of motion would /
could make the massive black hole "wobble"?
http://en.wikipedia.org/wiki/Spin-flip wrote:
<<A black hole spin-flip occurs when the spin axis of a rotating black hole undergoes a sudden change in orientation due to absorption of a second (smaller) black hole. Spin-flips are believed to be a consequence of galaxy mergers, when two supermassive black holes form a bound pair at the center of the merged galaxy and coalesce after emitting gravitational waves. Spin-flips are significant astrophysically since a number of physical processes are associated with black hole spins; for instance, jets in active galaxies are believed to be launched parallel to the spin axes of supermassive black holes. A change in the rotation axis of a black hole due to a spin-flip would therefore result in a change in the direction of the jet.

Black hole spin-flips were first discussed in the context of a particular class of radio galaxy, the X-shaped radio sources. The X-shaped galaxies exhibit two, misaligned pairs of radio lobes: the "active" lobes and the "wings". It is believed that the wings are oriented in the direction of the jet prior to the spin-flip, and that the active lobes point in the current jet direction. The spin-flip could have been caused by absorption of a second black hole during a galaxy merger.>>

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by Alfred » Thu Dec 06, 2012 6:27 pm

Ann wrote:
Alfred wrote:"Detailed analyses indicate that the central galaxy, also known as 3C 348, is actually over 1,000 times more massive than our Milky Way Galaxy, and the central black hole is nearly 1,000 times more massive than the black hole at our Milky Way's center."

Can anyone please try and describe the concequences of such a massive Central black hole in our Milky Way galaxy? Would it be possible to live on Earth?
My gut feeling is that such a titanic black hole would indeed be dangerous, mostly because of the incredible jets it spews out. And if the black hole is rotating or the jets are precessing, then maybe very large parts of that galaxy regularly get showered by whatever nasty radiation or energetic particles or the like are found in those jets. I wouldn't like being on the receiving end of such a jet in the Milky Way. All things considered, I believe that huge black holes are dangerous, mostly because they have such cosmic outbursts when they eat.

Ann
What sort of motion would / could make the massive black hole "wobble"?

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by Alfred » Thu Dec 06, 2012 6:20 pm

Spif wrote:
Alfred wrote:"Detailed analyses indicate that the central galaxy, also known as 3C 348, is actually over 1,000 times more massive than our Milky Way Galaxy, and the central black hole is nearly 1,000 times more massive than the black hole at our Milky Way's center."

Can anyone please try and describe the concequences of such a massive Central black hole in our Milky Way galaxy? Would it be possible to live on Earth?
We have a large central black hole in our galaxy but it is only on the order of 1 million solar masses rather than the billion solar masses of the galaxy in the APOD picture above. Also, our black hole is relatively quiet while the one in Hercules A is busy actively ingesting lots of material that is falling into it. Ours was presumably active in the past but is apparently mostly done eating.

I believe active massive black holes emit most of their dangerous radiation in jets out the poles. There may be heightened cosmic ray radiation around the center of such a galaxy too, but I think not enough to be dangerous to the mid to outer reaches where life is most likely to evolve in a galaxy. Active black holes also emit a lot of X-ray light from their accretion disks but that is only dangerous when close and much of that I believe gets attenuated by a ring cloud of dust that snuggles up close to the black hole. So the central black holes are pretty much only dangerous up close and at any distance along the polar axes.

A misconception that some people have is that black hole gravity is somehow dangerous or far reaching. In fact that is not true. Black hole gravity is only dangerous around the event horizon. If our sun were a black hole, we could orbit it and get along just fine (aside from the lack of luminous emission).
There is a factor 1000 mentioned with regards to the size of the central black hole and the size of the Galaxy... Is there any evidence to suggest that big black holes reside in big galaxies, and vice versa? I assume Our sun would be racing at great speeds becauce of the gravity from the black hole monster?

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by BMAONE23 » Thu Dec 06, 2012 6:01 pm

I would think that IF the jets were Polar and IF the poles pointed perpendicular to the galaxy disk and IF the host galaxy were a disk with a planar stellar galactic orbit, then the odds of life being there are far greater than in the chaotic orbits within an elliptical galaxy. Orbits within elliptical galaxies would tend to have a far greater chance of encountering the radiation from the jets

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by muffin » Thu Dec 06, 2012 5:54 pm

a bit late to the debate -

question from a non-astronomer: the 2 jets look a lot like cigarette smoke, especially the left one. does that mean that the same laws [or descriptions?] of turbulence are going on here? it seems pretty remarkable to find the similarity.. it doesnt look like there's self-similar patterning inside the puffs..

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by Ann » Thu Dec 06, 2012 5:33 pm

Alfred wrote:"Detailed analyses indicate that the central galaxy, also known as 3C 348, is actually over 1,000 times more massive than our Milky Way Galaxy, and the central black hole is nearly 1,000 times more massive than the black hole at our Milky Way's center."

Can anyone please try and describe the concequences of such a massive Central black hole in our Milky Way galaxy? Would it be possible to live on Earth?
My gut feeling is that such a titanic black hole would indeed be dangerous, mostly because of the incredible jets it spews out. And if the black hole is rotating or the jets are precessing, then maybe very large parts of that galaxy regularly get showered by whatever nasty radiation or energetic particles or the like are found in those jets. I wouldn't like being on the receiving end of such a jet in the Milky Way. All things considered, I believe that huge black holes are dangerous, mostly because they have such cosmic outbursts when they eat.

Ann

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by Spif » Thu Dec 06, 2012 4:58 pm

Alfred wrote:"Detailed analyses indicate that the central galaxy, also known as 3C 348, is actually over 1,000 times more massive than our Milky Way Galaxy, and the central black hole is nearly 1,000 times more massive than the black hole at our Milky Way's center."

Can anyone please try and describe the concequences of such a massive Central black hole in our Milky Way galaxy? Would it be possible to live on Earth?
We have a large central black hole in our galaxy but it is only on the order of 1 million solar masses rather than the billion solar masses of the galaxy in the APOD picture above. Also, our black hole is relatively quiet while the one in Hercules A is busy actively ingesting lots of material that is falling into it. Ours was presumably active in the past but is apparently mostly done eating.

I believe active massive black holes emit most of their dangerous radiation in jets out the poles. There may be heightened cosmic ray radiation around the center of such a galaxy too, but I think not enough to be dangerous to the mid to outer reaches where life is most likely to evolve in a galaxy. Active black holes also emit a lot of X-ray light from their accretion disks but that is only dangerous when close and much of that I believe gets attenuated by a ring cloud of dust that snuggles up close to the black hole. So the central black holes are pretty much only dangerous up close and at any distance along the polar axes.

A misconception that some people have is that black hole gravity is somehow dangerous or far reaching. In fact that is not true. Black hole gravity is only dangerous around the event horizon. If our sun were a black hole, we could orbit it and get along just fine (aside from the lack of luminous emission).

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by Alfred » Thu Dec 06, 2012 4:37 pm

"Detailed analyses indicate that the central galaxy, also known as 3C 348, is actually over 1,000 times more massive than our Milky Way Galaxy, and the central black hole is nearly 1,000 times more massive than the black hole at our Milky Way's center."

Can anyone please try and describe the concequences of such a massive Central black hole in our Milky Way galaxy? Would it be possible to live on Earth?

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by Spif » Thu Dec 06, 2012 2:43 pm

starsurfer wrote:
Horus wrote: Hi guys, is it me or do those jets look like they are turning counter clockwise?
The jet on the left coming towards us and the right one travelling away.
No I think that is an illusion. If that was the case, the left jet would appear blueshifted and the right one redshifted and if that was the case, then that would definitely have been mentioned in the article. However, I might be wrong as I haven't read the related paper (assuming there is a corresponding paper).

What you may be seeing is there could likely be a prevailing wind that is blowing the slowed ends of the jets back. Both the ambient gas and the galaxy are moving relative to the local cluster and that can induce a drift once the gas in the jets slows through multiple collisions.

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by starsurfer » Thu Dec 06, 2012 7:22 am

neufer wrote:
starsurfer wrote:
Horus wrote:
Hi guys, is it me or do those jets look like they are turning counter clockwise?
The jet on the left coming towards us and the right one travelling away.
No I think that is an illusion. If that was the case, the left jet would appear blueshifted and the right one redshifted and if that was the case, then that would definitely have been mentioned in the article. However, I might be wrong as I haven't read the related paper (assuming there is a corresponding paper).
The radio jet structure is simply a monochrome black & white radio wave intensity map that is color coded magenta to distinguish it from the Hubble background.

Besides which, there are no spectral lines to blue-shift or red-shift since the continuous synchrotron radiation comes from "relativistic electrons spiraling through magnetic fields."

The source black hole could well be slowly precessing so as to cause the slow moving jet exit regions to have the sort of "water spray" slow turning features that Horus suggests (or it could be simply an illusion as starsurfer suggests).
Thanks for the informative reply! I know hardly anything about radio galaxy jets, so I wish to apologise for misleading anyone with my rare episode of assuming a fact rather than actually reading it up and giving a reply based on genuine truth.

Re: APOD: Plasma Jets from Radio Galaxy Hercules A (2012 Dec

by rstevenson » Thu Dec 06, 2012 3:07 am

Strangerbarry wrote:...
Consider then a couple of scenarios about the probability of successful abiogenesis and what the universe might look like under those scenarios. ...
Two things you might want to have a look at which bear on this issue: the Drake Equation, which is a tool for estimating "the number of detectable extraterrestrial civilizations in the Milky Way galaxy," and the Fermi Paradox, which isn't really a paradox; it's just the question, "Where is everybody?".

Depending on how optimistic I'm feeling (which in turn depends on what I had for breakfast) I get an answer that can range from 10 to 100,000 using the Drake Equation, an answer which just brings me back to Fermi's question. Perhaps all we can conclude is that we're the first civilization that may (if we're very, very smart about fixing our current problems) eventually fill up the Milky Way galaxy. Or not.

Rob

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