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William of Ockham meets NGC 5907
Posted: Sat Jun 21, 2008 10:35 am
by henk21cm
Sputnick wrote:
These are what I see the curving wisps as .. and they are curved opposite to each other because they are on opposite sides of the galaxy .. stars being pulled out from their spirals by the tumbling motion.
Ask yourself the question how some stars in a rotating galaxy would jump out of the main rotational plane, perpendicular to their original motion, while the bulk of the stars still rotate in their original plane.
Next, ask yourself the question why not all -or a large percentage of- galaxies show these faint trails like NGC 5907, perpendicular to the main rotational plane.
Posted: Sat Jun 21, 2008 12:48 pm
by Nereid
Four separate threads on the same APOD merged into one.
Re: William of Ockham meets NGC 5907
Posted: Sat Jun 21, 2008 3:54 pm
by Sputnick
henk21cm wrote:Sputnick wrote:
These are what I see the curving wisps as .. and they are curved opposite to each other because they are on opposite sides of the galaxy .. stars being pulled out from their spirals by the tumbling motion.
Ask yourself the question how some stars in a rotating galaxy would jump out of the main rotational plane, perpendicular to their original motion, while the bulk of the stars still rotate in their original plane.
Next, ask yourself the question why not all -or a large percentage of- galaxies show these faint trails like NGC 5907, perpendicular to the main rotational plane.
Henck & y'all -- Of course I admit my theorem of tumbling is not proven fact, just something I believe by instinct and observation to be fact, but if it is fact, the stars in the wispy trail do not jump out .. they are pushed out by resistance to the Dark Matter and/or Dark Energy surrounding the galaxy. That they are pushed out at opposing ends is because the galaxy is tumbling on an axis across the plane at the mid point of the image as we are looking at it. At these opposite ends the speed of the tumble, however slow, and I think it is wonderfully slow, is sufficient to create the necessary resistance. If the speed of the tumble could be determined, the mass of the Dark Matter and/or Dark Energy might be able to be determined by its effect on the stars pushed out. I do not think all galaxies tumble .. the spinning plane of some might be as true as a frisbee, while others might wobble. This one, though, to me, is obviously tumbling. This is fun .. wonderful wonderful speculation. I appreciate you all.
Posted: Sat Jun 21, 2008 4:15 pm
by Sputnick
Bystander, or someone else - please explain to me how to find the url which will stay with the photo after the next (up to date) photo is posted.
Thanks .. and please explain as if to a simple minded person (only so I might be able to properly pass along the information to a simple minded person of course).
Posted: Sat Jun 21, 2008 4:34 pm
by Case
Sputnick wrote:please explain to me how to find the url which will stay with the photo after the next (up to date) photo is posted.
Maybe there's an easier way, but here's how I do it:
Today's APOD is at
http://antwrp.gsfc.nasa.gov/apod/
Near the bottom of the page, between the lines, there are arrows on the left side and on the right side which will navigate to the previous and next day. Go to the previous day's page "<", then back to the next day ">". Now your browser will have the dated URL in the address field.
http://antwrp.gsfc.nasa.gov/apod/ap080619.html
Look how it says ap080619.html at the end, where "080619" is year (08), month (06), day (19).
So the APOD for e.g. January 13th, 2003 (03-01-13) will be on page
ap030113.html. Works for every APOD.
Posted: Sat Jun 21, 2008 4:46 pm
by NoelC
The easy way is to go to yesterday's photo by clicking on the < link, then come back to today's photo by clicking on the > link. The page URL will then be the one containing today's date, as Case pointed out above.
-Noel
Re: William of Ockham meets NGC 5907
Posted: Sat Jun 21, 2008 7:08 pm
by iampete
henk21cm wrote: . . . Next, ask yourself the question why not all -or a large percentage of- galaxies show these faint trails like NGC 5907, perpendicular to the main rotational plane.
While I'm not a proponent of the "tumbling" hypothesis, let me proffer the following (in the spirit of Billy Ockham).
It does not seem appropriate to me to consider many of the things we see as singular, "one of" type of events. If one accepts the explanation in the caption as credible, is it not reasonable to expect that similar circumstances (i.e., satellite galaxy ingestion) will result in similar manifestations in other galaxies and to consider that "trails" of this type are more-or-less "normal" when smaller galaxies are ingested? It does not seem unreasonable to me that the fact that we don't observe them ubiquitously is related to things like time since ingestion, different ingestion geometries, different galactic mass ratios, different illumination angles, etc., etc. It seems as if that might be a more fruitful approach rather than to consider NGC 5907 as a completely unique, one-of-a-kind galaxy.
Just like the rings of Saturn, which, many years ago, were taught to be a singular and unexplained planetary anomaly, have now been explained and found to be a "normal" characteristic based on our knowledge of physical laws. In fact, every planet has a set of rings, although most are so tenuous that they are difficult to discern, or they have been dissipated by other phenomena. It took until 1979 for the Jovian rings to be found by Voyager, using observational techniques not feasible until that time, and, several years later, the rings of Uranus and Neptune.
Posted: Sat Jun 21, 2008 7:13 pm
by Sputnick
Case - Thou art a genuius. Thanks .. and to you also, Noel, Noel, the angels did say, to a certain poor shepherd in fields as they lay. Poor me, I can't remember if that was 'the angels did say' or 'the angels did sing' - but 'say' rhymes with 'lay, whereas if the word was 'sing' the shepherds would have had to have been on a fling .. like, flinging rocks at wolves. I wonder if there are wolves on Mars which eat the rabbits .. or are Martians vegetarians perhaps?
Posted: Sat Jun 21, 2008 7:28 pm
by Sputnick
Also, Iampete, because the trails/tails are so faint, the direction of the tumble might be critical to detection of the trails .. or, if a spiral is tumbling through Dark Matter/Dark Energy of little mass, friction would not be enough to create trails/tails. Please understand I use the word 'friction' in place of more appropriate terms physicists might use.
Re: Stellar Stream surrounding NGC 5907
Posted: Sat Jun 21, 2008 7:47 pm
by Sputnick
jgabany wrote:Hello danbonnick:
These are good questions- thank you for asking!
The streams seen in this picture represent the remains of a long lost satellite galaxy that was gravitationally torn to shreds and digested by the large spiral, seen edge on in this image. Very little of the former companion remains. Measurements by the team of researchers who studied this galaxy and its rings had difficulty finding any traces of stellar activity. The rings appear to be comprised mostly of dust.
One of the researchers used a powerful computer to prepare an animation that illustrates how the rings were formed. Here's a link that you may find interesting:
http://www.cosmotography.com/images/ngc ... ation.html
As the animation depicts, the small satellite was orbiting the larger companion (not shown) and, over time, was simply stretched by tidal forces originating from the spiral's center. It is interesting to note that the rings are elliptical in shape- the NGC 5907's central region lies at one of the foci.
Dark matter most likely played a part in the events that destroyed the original satellite- to what extent, I can only speculate.
I hope this, at least partially, answers your questions.
Jay
Nice animation .. and the galaxy which is creating the trails appears to be tumbling .. I think a drink to celebrate would be appropriate .. especially as I since watching the animation I've come to believe that the trails were created by this very galaxy, in what is to me at this stage of thought a dizzingly fast tumble.
Re: William of Ockham meets NGC 5907
Posted: Sat Jun 21, 2008 9:46 pm
by henk21cm
iampete wrote:
While I'm not a proponent of the "tumbling" hypothesis, let me proffer the following (in the spirit of Billy Ockham).
IMHO tumbling of the main galaxy is rather unlikely. Conservation of impulse moment of the main galaxy is the main reason. As you eloquently pointed out - and in doing so, taught me several new words- the one of a kind hypothesis: just one trail, just one set of rings, just one atmosphere, is too artificial. Furthermore the explanation the APOD writers have given, is not unlikely. What is harder to grasp is, that the companion galaxy completely has disappeared. So it is more 'astronomical forensics' to find out what might have happened.
I just wonder, whether such a trail of stars is also (faintly) visible around our galaxy, caused by the two Magellanic clouds. As you were proffering, the plane of the orbiting system must be right, the angle of view, etc. These are all parameters we can not influence. Not in the least the abundant presence of stars in our own galaxy, allowing the stars in the trail to hide between these stars.
Posted: Sun Jun 22, 2008 12:54 am
by Sputnick
Do we agree that the 'companion galaxies' are speculation? Here's another idea which I got by watching the simulation .. the trails were created by the one galaxy tumbling in orbits at a fast rate after being captured by a massive and as yet undetected black hole .. the trails being stars ejected from the spiral's core .. this resulting in the galaxy's thin shape. I speculate the trails we can see are bordered by fainter trails of stars from the spirals. The galaxy as it is in the photo appears to have lost most of the momentum of tumbling, and is now tumbling at a greatly reduced speed. (?)
Henk - I do not undertand "Conservation of impulse moment" but I can see the curving trails/tails at either end of the galaxy as evidence for tumbling.
Re: William of Ockham meets NGC 5907
Posted: Sun Jun 22, 2008 2:51 am
by starnut
henk21cm wrote:
I just wonder, whether such a trail of stars is also (faintly) visible around our galaxy, caused by the two Magellanic clouds. As you were proffering, the plane of the orbiting system must be right, the angle of view, etc. These are all parameters we can not influence. Not in the least the abundant presence of stars in our own galaxy, allowing the stars in the trail to hide between these stars.
The Magellanic Stream was detected in the 1970s.
http://apod.nasa.gov/apod/ap980826.html
http://en.wikipedia.org/wiki/Magellanic_Stream
Gary
Re: William of Ockham meets NGC 5907
Posted: Sun Jun 22, 2008 9:58 am
by iampete
henk21cm wrote: . . . the companion galaxy completely has disappeared. So it is more 'astronomical forensics' to find out what might have happened. . .
Disappeared from our view, certainly, but there is an awfully large volume of space in that galaxy that we can't see. Again, things like timing, could be important: had we looked a couple of million years ago or were we to look again a couple of million years from now, we might see the smaller galaxy entering into or exiting from the plane of the larger.
I like your choice of "astronomical forensics" as a descriptor. I would be interested to hear if that could be done in this case, and possibly others, and to learn just what sort of confidence levels could be assumed in the accuracy of such forensics, given that the timescales necessary to actually observe whether such conclusions were correct or not are so large.
Re: William of Ockham meets NGC 5907
Posted: Sun Jun 22, 2008 10:14 am
by iampete
The caption for the APOD indicates that this stream is a gas cloud, while the wiki article could be interpreted to imply, but does not explicitly state, the the stream contains stars/star formation regions. From wiki: "Observations of individual stars gave us the star formation history.", but I can't tell if that's referring to stars in the Magellanic Clouds, or in the stream.
Is this Magellanic stream similar to the streams (which include stars) that you and jgabany mentioned earlier, or is it just gas and dust?
Re: William of Ockham meets NGC 5907
Posted: Sun Jun 22, 2008 11:07 am
by henk21cm
Nice to see that NGC5907 is not one of a kind. Nevertheless two of a kind is not a huge number in astronomical sense. Combined with a slight warping as observed in both galaxies, in our galaxy's case two companion galaxies, and the
simulation jgabany has brought to our attention, a brittle conceptual model emerges.
sputnick wrote:Do we agree that the 'companion galaxies' are speculation?
As
iampete points out, the companion(s) might be temporary hiding in our line of sight, obscured in the plane of the 'main' galaxy. The existence of a companion now or earlier is rather a working hypothesis than speculation. Another threat is that we do not see a lot of these star streams. We are dealing until now with 'isolated observations' and you know what the consequences are: generalization based on a few observations leads to weird conclusions.
(As an example, Jacob Bronovsky told an amusing story that an alien space ship lands in the polar regions of northern Canada. These aliens come to the conclusion that our world is inhabited by polar bears and seals only.)
sputnick wrote:The galaxy as it is in the photo appears to have lost most of the momentum of tumbling, and is now tumbling at a greatly reduced speed.
The only tumbling i see in the simulation is that of the companion galaxy, leaving a trail of stars or matter. I came to that conclusion since the galaxy shown in the animation orbits around a massive center of gravity, which is not shown (and for which i assume it is the main galaxy). As pointed out earlier it is very unlikely that the main galaxy is tumbling, because of the law of conservation of angular momentum.
Finally: the law of conservation of inpulse moment. That is my error, due to a wrong translation. In English it is called 'angular momentum'. See
(if needed).
Conservation of angular momentum is responsible for Keplers second law. Similarly it prevents e.g. gyroscopes and cyclists from tumbling.
Re: William of Ockham meets NGC 5907
Posted: Sun Jun 22, 2008 4:22 pm
by Sputnick
henk21cm wrote:
Nice to see that NGC5907 is not one of a kind. Nevertheless two of a kind is not a huge number in astronomical sense.
My response: Two of a kind is rare, and I think it signifigant that the trails are also rare .. and when you have the rare, thin galaxy occuring with the rare trails, I see as probable that the two are connected .. that the trails contain the bulk of what was a normal galaxy, thinned by the process of trail extraction.
sputnick wrote:Do we agree that the 'companion galaxies' are speculation?
Henck: As
iampete points out, the companion(s) might be temporary hiding in our line of sight, obscured in the plane of the 'main' galaxy. The existence of a companion now or earlier is rather a working hypothesis than speculation.
My response: In my understanding of the English language 'Hypothesis' is connected in meaning with 'hypothetical' - 'speculation' is another word for both.
sputnick wrote:The galaxy as it is in the photo appears to have lost most of the momentum of tumbling, and is now tumbling at a greatly reduced speed.
The only tumbling i see in the simulation is that of the companion galaxy, leaving a trail of stars or matter.
My response: I apologize for wording my post in a way in which someone could misunderstand my meaning. I did not mean I saw the large galaxy in the simulation, I understood that the simulation was of a companion galaxy; however, as I do not believe there were compaion galaxies, I think the large galaxy could be substituted as the galaxy in the simulation. I will repeat that while the favoured view of the trails are from small galaxies orbiting the large galaxy, my opinion is that the large galaxy was captured by and is orbiting an invisible mass, perhaps a huge black hole.
Henck: Finally: the law of conservation of inpulse moment. That is my error, due to a wrong translation. In English it is called 'angular momentum'. See
(if needed).
Conservation of angular momentum is responsible for Keplers second law. Similarly it prevents e.g. gyroscopes and cyclists from tumbling.
My response: I played with a small but substantial, steel gyroscope as a boy .. and while the spin prevented the gyroscope from tipping off it's pointed pedestal, if the gyroscope were set spinning and then thrown through the air it certainly would tumble.
Posted: Sun Jun 22, 2008 4:25 pm
by Sputnick
Would a scientist here please explain the scientific meaning of "working hypothesis"? Please and thank you.
Re: William of Ockham meets NGC 5907
Posted: Sun Jun 22, 2008 5:55 pm
by Qev
henk21cm wrote:I just wonder, whether such a trail of stars is also (faintly) visible around our galaxy, caused by the two Magellanic clouds. As you were proffering, the plane of the orbiting system must be right, the angle of view, etc. These are all parameters we can not influence. Not in the least the abundant presence of stars in our own galaxy, allowing the stars in the trail to hide between these stars.
There's also the
Sagittarius Dwarf Tidal Stream...
Sputnick wrote:My response: I played with a small but substantial, steel gyroscope as a boy .. and while the spin prevented the gyroscope from tipping off it's pointed pedestal, if the gyroscope were set spinning and then thrown through the air it certainly would tumble.
I'm pretty certain a free-falling gyroscope isn't going to tumble, unless an outside force is acting on it.
Re: William of Ockham meets NGC 5907
Posted: Sun Jun 22, 2008 6:42 pm
by Sputnick
Sputnick wrote:My response: I played with a small but substantial, steel gyroscope as a boy .. and while the spin prevented the gyroscope from tipping off it's pointed pedestal, if the gyroscope were set spinning and then thrown through the air it certainly would tumble.
Qev - I'm pretty certain a free-falling gyroscope isn't going to tumble, unless an outside force is acting on it.[/quote]
You're right, Qev, with the point being 'an outside force acting on it'. If generally accepted theorem is correct, something outside of the galaxies set them in motion. If I were in space, and hurled a spinnng gyroscope in such a way that I caused it to tumble as it flew, I make a guess that it's anybody's guess as to when it becomes "free falling". In the case of this galaxy, I think that outside force is a Black Hole which captured the galaxy so suddenly, that as its forward direction was altered suddenly and drastically, it began to tumble, as it shows in the simulation.
Tumbling Galaxies
Posted: Sun Jun 22, 2008 7:09 pm
by astrolabe
Hello All,
I'm assuming, of course, that tumbling is being used as an additional possible motion characteristic of a galaxy (or anything else for that matter), something other than just rotation. My first thought is, yes, galaxies rotate and tumble, but only with outside influence. A bicycle spinning in a vertical plane could be considered tumbling but I think the spirit of the word is to mean motion that is perhaps not inherently natural for an object.
If a galaxy was to be tumbling one would think that the trail would have more of a modulated appearance like waves and troughs as the object tumbled from face on to flat, again and again, until an outside influence or eventually dark matter slowed or stopped it. Is dark matter considered static or fluid? That being said, maybe they all started out tumbling!
One last comment: nothing says tumbling would be perfect in it's geometry were it to happen. The axis could be anywhere across the galactic plane for example with two thirds of the object on one side of the axis and a third on the other with the galaxy sort of "lobing" along with what would look like a hop in the trajectory followed by a kind of hi/lo alternating tail behind it. Ya' THINK
P.S. Welcome to the new members
![Very Happy :D](./images/smilies/icon_biggrin.gif)
Tumbling thoughts
Posted: Sun Jun 22, 2008 9:22 pm
by iampete
My thoughts from a layman's perspective:
The shape of the galaxy under discussion in this thread suggests that the angular momentum (AM) vector is pretty much perpendicular to the galactic plane. Since the galaxy is not a single solid object, for it to be "tumbling" (i.e., a non-trivial component of this vector being parallel to the galactic plane), should result (over time) in the change of the galaxy's shape such that the vector is again perpendicular to the galactic plane. Therefore, any "tumble" would not persist unless a constant torque were to continually change the net AM vector.
In my opinion, the very slight "S"-shape of the galaxy in the edge-on view may be the result of a long-ago change in the original angular momentum vector, with the structures at the greatest distance from the galactic center having not quite finished with their re-alignment (although I'd prefer someone with a better feel for the physics to comment on that). The change in direction of the AM vector is likely to have been the result of the combination of the AMs of the original (massive) galaxy and the apparently ingested small galaxy. However, this change in direction of the AM vector is a "single" small change ("single" but of mega- or giga-year duration), not a continuous change which would cause a "tumble".
Bottom line: galaxies with a persistent "tumble" should not be possible.
Does this make sense, or am I missing something?
Re: Tumbling thoughts
Posted: Mon Jun 23, 2008 12:08 am
by Sputnick
iampete wrote:My thoughts from a layman's perspective:
..... The change in direction of the AM vector is likely to have been the result of the combination of the AMs of the original (massive) galaxy and the apparently ingested small galaxy. However, this change in direction of the AM vector is a "single" small change ("single" but of mega- or giga-year duration), not a continuous change which would cause a "tumble".
Bottom line: galaxies with a persistent "tumble" should not be possible.
Does this make sense, or am I missing something?
What's missing is why the 'missing' companion galaxies are so accepted as having been there in the first place. The 'evidence' is pure speculation,
but I am disappointed that the 'missing' galaxies are so present in the minds of most of you as to disallow any real speculation of the possiblility that the existing galaxy created the trails. However, I am satisfied that my initial observation of the possibility of a tumbling galaxy has been credited as being at least possible .. although I am certain it is a fact.
Posted: Mon Jun 23, 2008 1:46 am
by Qev
Sputnick wrote:If I were in space, and hurled a spinnng gyroscope in such a way that I caused it to tumble as it flew, I make a guess that it's anybody's guess as to when it becomes "free falling".
I don't think it quite works like that. You can't "set a gyroscope tumbling" without applying a constant torque, unless I've completely forgotten how angular momentum works...
Posted: Mon Jun 23, 2008 12:50 pm
by Alietr
Does anyone know what the blurred object in the upper right-hand corner is? It could be "just" another galaxy, but it doesn't look like it would be one.