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Fraser
2004-Sep-07, 07:33 PM
SUMMARY: The latest image released by the Gemini Observatory shows a group of galaxies tearing each other apart 300 million light-years away. The galaxies are members of Stephan's Quintet, and their shapes are completely warped by gravitational interactions that have been going on for millions of years. This ongoing chaos has spawned huge stellar nurseries - hotspots of furious star formation. They'll keep on interacting for a few more million years before merging into larger objects; the smaller galaxies will be completely torn apart.

What do you think about this story? Post your comments below.

antoniseb
2004-Sep-07, 08:03 PM
An image of Stephan's Quintet was the thing that pulled me outside of just being interested in lunar and planetary astronomy, and made me interested in the galaxies too. I was about seven years old.

TuTone
2004-Sep-07, 08:06 PM
If theres any ETs in any of those galaxies.........God bless them! :)

VanderL
2004-Sep-07, 08:47 PM
Stephan's Quintet is one of the examples from which Halton Arp's argues that there must be intrinsic redshifts. The foreground galaxy (middle top) clearly shows an interaction tail to the right. He argues that the only possible way to get such a tail is interaction with another galaxy. The only candidates are the higher redshift galaxies that are clearly disturbed and interacting. The only problem is that the top galaxy has a lower redshift placing it 8 times closer than the other galaxies.

There is more to this puzzle, here (http://www.gemini.edu/project/announcements/press/2004-7.html) is additional information where molecular hydrogen is shown seemingly overlaying some of these galaxies (including the lower redshift galaxy). Additionally, HII regions are found with comparable redshift as the disturbed galaxies, placing it in the same cluster, although they seem unrelated and are found in an "empty" region.
Also, in my opinion, the lower redshift galaxy shows comparable resolution of details (indicating equal distance) and is of comparable size (instead of 8 times smaller), which should make the solution to the puzzle really simple: redshift is not a distance indicator and some intrinsic redshift mechanism must exist.

Cheers.

antoniseb
2004-Sep-07, 09:13 PM
Originally posted by VanderL@Sep 7 2004, 08:47 PM
in my opinion, the lower redshift galaxy shows comparable resolution of details (indicating equal distance) and is of comparable size (instead of 8 times smaller)
There are interaction streamers coming out of the distant galaxies in lots of directions, and they are all pretty much the same red-shift, except the forground galaxy.

So the question is this: Stephan's quintet has been studied quite a bit. What is the redshift of the supposed bridge to the forground galaxy? Does it slide up the redshift scale, or is it purely the redshift of one or the other?

Halton C. Arp's research is old, and predates the use of modern astronomy equipment. There is no bridge between the forground galaxy and background galaxy. Also, there is no evidence that the forground galaxy has been perturbed in any way recently, whereas the other galaxies are all over the place, and experiencing masive starbirth.

BTW, the closer galaxy should be eight times bigger, not smaller.

John L
2004-Sep-07, 09:31 PM
If redshift is a function of the stars, the material they are made of, their age, or some factor other than distance, then the bridge would not slide along the redshift scale between the value of one galaxy and the other. The bridge would be stars and gas stripped off one galaxy by the other, so, if redshift is not distance related, then its redshift should be the same as the galaxy it was stripped from. It is a shame they are so far away that we can't use something like paralax to determine their true distance.

Guest
2004-Sep-07, 09:41 PM
Hi Antoniseb,


So the question is this: Stephan's quintet has been studied quite a bit. What is the redshift of the supposed bridge to the forground galaxy?

There is no obvious bridge because the space between the galaxies in question shows nor room for it. Maybe some dimming of the higher redshift should be visible from the absorption by the lower redshift galaxy, but I can't see it and I'm not sure those data are available.
Arp's work is very important, while the man is old, his work isn't (he still publishes). You seem to think that this redshift controversy is over, but there are still articles pointing to the same problem. Also the mechanisms for intrinsic redhift are actively researched (see CREIL, plasma redshift and others).

The tail points away from the disturbed galaxies, but tails are always interpreted as caused by gravitational interaction; the only possible candidates to disturb the low redshift galaxy are the higher redshift galaxies. That's the point, they shouldn't be interacting if redshift really is a distance indicator.


BTW, the closer galaxy should be eight times bigger, not smaller.

For galaxies to appear the same size while at different distances, shouldn't that make the closer galaxy smaller?

Cheers.

RenwickW
2004-Sep-08, 03:14 AM
If you were living on a planet in a galaxy being 'torn apart', as recently observed by the Gemini observatory, would you be aware it was happening? Would your planet /solar system be destroyed? Or is it all happening so slowly (over millins of years) that you would be unconcerned about it?

antoniseb
2004-Sep-08, 12:17 PM
Originally posted by RenwickW@Sep 8 2004, 03:14 AM
would you be aware it was happening? Would your planet /solar system be destroyed? Or is it all happening so slowly (over millins of years) that you would be unconcerned about it?
If two similar sized spiral galaxies were merging or pasing through each other's centers, you'd know about it, since there would be some very high speed asteroid and comet hits to your planet. These would not be an every day occurence, but all it would take would be one.

If two galaxies were passing by each other close enough to distort each other's spiral arms, you might know because there would be an era of intense star formation and there would be a small chance that you'd be affected by a nearby supernova.

antoniseb
2004-Sep-08, 12:26 PM
Originally posted by Guest@Sep 7 2004, 09:41 PM
For galaxies to appear the same size while at different distances, shouldn't that make the closer galaxy smaller?
Oh I see, You wre talking about actual size, and I was talking about how it appeared in the photograph. Yes, the forground galaxy [NGC 7320] must be a small one compared to the more distant interacting ones. It is, in fact, an undisturbed small elliptical galaxy, whereas the others are large spirals.

Maybe some dimming of the higher redshift should be visible from the absorption by the lower redshift galaxy, but I can't see it
Since NGC 7320 is an elliptical, it doesn't have a halo of gas and dust to obscure the background galaxies. No dimming should be observed.

You seem to think that this redshift controversy is over
I don't think it's over, but Stephan's Quintet is not a counter-example. There is no bridge to the forground galaxy.

Travis Rector
2004-Sep-08, 09:48 PM
Originally posted by RenwickW@Sep 8 2004, 03:14 AM
If you were living on a planet in a galaxy being 'torn apart', as recently observed by the Gemini observatory, would you be aware it was happening? Would your planet /solar system be destroyed? Or is it all happening so slowly (over millins of years) that you would be unconcerned about it?
Hi-

I'm the astronomer who made the Gemini image of Stephan's Quintet. If you were living on a planet in a galaxy that is gravitationally interacting you probably wouldn't be affected much.
These interactions take place over millions of years, but presumably your sun and planet were
formed billions of years prior (like our sun). You could be affected adverseley if your sun had a
close interaction with a star from another galaxy- close enough that it affected the orbits of the
planets around your sun, possibly ejecting your planet from its orbit. This is very unlikely. Another possibility is that, when galaxies undergo these interactions, it triggers rapid star formation in clouds of gas inside the galaxies. If you were near one of these clumps of star formation, your planet may be affected by massive stars that go supernova at the end of their
lives. Overall though I would image it'd be pretty spectacular to see- like giant orion nebulas.

-Travis

Guest
2004-Sep-08, 10:24 PM
Originally posted by antoniseb+Sep 8 2004, 12:26 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (antoniseb @ Sep 8 2004, 12:26 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-Guest@Sep 7 2004, 09:41 PM
For galaxies to appear the same size while at different distances, shouldn&#39;t that make the closer galaxy smaller?
Oh I see, You wre talking about actual size, and I was talking about how it appeared in the photograph. Yes, the forground galaxy [NGC 7320] must be a small one compared to the more distant interacting ones. It is, in fact, an undisturbed small elliptical galaxy, whereas the others are large spirals.

Maybe some dimming of the higher redshift should be visible from the absorption by the lower redshift galaxy, but I can&#39;t see it
Since NGC 7320 is an elliptical, it doesn&#39;t have a halo of gas and dust to obscure the background galaxies. No dimming should be observed.

You seem to think that this redshift controversy is over
I don&#39;t think it&#39;s over, but Stephan&#39;s Quintet is not a counter-example. There is no bridge to the forground galaxy. [/b][/quote]
Observations have shown that there appears to be overlapping material, but there is no evidence for a physical bridge of material between NGC 7320 and the other galaxies. Furthermore, NGC 7320 shows no evidence of gravitational interaction. The other galaxies are very distorted, with star formation triggered in the impacted regions. NGC 7320 appears to be very circular, with normal rates of star formation distributed throughout the galaxy. The evidence for non-cosmological origins to the redshifts in this cluster is very tenuous.

-Travis

VanderL
2004-Sep-09, 04:32 PM
Thanks Travis,


NGC 7320 appears to be very circular, with normal rates of star formation distributed throughout the galaxy. The evidence for non-cosmological origins to the redshifts in this cluster is very tenuous.


But it does have a tail visible in the link a few posts back, and such a tail would suggest interaction with another galaxy, if not the disturbed galaxies, which one would be the cuprit then?

Btw, the tail has the same direction and curve as the righthand side galaxy (don&#39;t know the NGC number), and the resolution of detail in the galaxies seems to indicate that the galaxies are comparable in size and distance, all coincidence? If it wasn&#39;t for the redshift values, I think a case cood be made that the galaxies are a cluster.
And isn&#39;t it true that small ellipticals are always accompanied by large spiral galaxies? That would seem to make NGC 7320 an orphan, right?


Cheers.

VanderL
2004-Sep-10, 12:29 PM
Talking about coincidence, today there was this paper (http://xxx.lanl.gov/pdf/astro-ph/0409215) in the arXives that shows one of the galaxies of Stephan&#39;s quintet with an apparently ejected quasar. Just to add to the redshift controversy I mentioned earlier.
The galaxy in question is NGC 7319, I&#39;m not sure if that galaxy is in the Gemini picture.
What do you think of this?

Cheers.

antoniseb
2004-Sep-10, 01:06 PM
Originally posted by VanderL@Sep 10 2004, 12:29 PM
The galaxy in question is NGC 7319, I&#39;m not sure if that galaxy is in the Gemini picture.
What do you think of this?
NGC 7319 is in the Gemini picture, it is the disrupted elliptical near the center.
The paper is by Arp, Burbage, et. al. and I think the conclusions show a decided bias toward their theory.

To me, I think that the QSO is a lensed object seeming brighter than it should owing to the elliptical galaxy its light is going through. This increases the likelyhood that we&#39;d see one there.

Since NGC7319 is fairly nearby, we should soon be able to get more detailed observations that will confirm or refute the conclusion that the QSO is part of the Quintet. Such work could happen as part of a study of dark matter halo structure.

BTW, I&#39;m delighted to see I&#39;m not the only one skimming arXiv on a daily basis&#33;

VanderL
2004-Sep-10, 02:22 PM
Hi Antoniseb,

You&#39;re postings and referrals to the arXive papers showed me where a great deal of information can be found, for "free". I mean, most times you need expensive journal subscriptions, which in some cases are still needed, but this database is quite enough to get an idea what&#39;s happening "out there".


To me, I think that the QSO is a lensed object seeming brighter than it should owing to the elliptical galaxy its light is going through. This increases the likelyhood that we&#39;d see one there.

How do you prove that this quasar is lensed by the galaxy there seems only very little material at the QSO location. In the paper the authors go into detail on the possibility the QSO is a background object. Did you see the image and data on the spectra?

On the paper itself, the bias you say exists, is an unscientific way to respond to these findings, imo. There are a number of authors publishing on the redshift controversy, Bell, Russell, Burbidge, Arp and others. And other than Arp&#39;s ejection model (which does not give a mechanism for the high redshift), there are no theories yet that exactly explain why quasars are found near active spiral galaxies. There are observations, and regardless of the model you think is correct, these observations must be addressed. Up until now the findings are published (sometimes after a big hassle) and ignored.

The bias can be said to work the other way as well, but that would be equally unscientific. I think in this case "believing is seeing" is the likely cause. If you believe that redshift is a solid distance indicator, all the examples that opponents can gather are simply dismissed as coincidental. If, on the other hand, you believe that it is an open question, more detailed study is required but I don&#39;t see that happening.

I think that there are a number of valid reasons to question the redshift=distance rule, and since the consequences of finding that intrinsic redshifts are real are important for astronomy/cosmology it seems logical to keep investigating this question.

At this moment there are 2 approaches that could lead to a solution of the controversy: the observational approach: keep gathering information on high redshift objects and their surroundings (proper motion studies would give conclusive evidence on ejections, I think).
The other approach is coming up with a mechanism that explains redshift as a physical process other that through a Doppler effect (plasma redshift, CREIL, Compton effect etc).

In the meantime the question regarding the grouping and possible interactions of the galaxies in Stephan&#39;s Quintet can only be answered by detailed studies, and I hope the people doing this research will continue this important work.

Cheers.

antoniseb
2004-Sep-16, 12:31 AM
Hi VanderL

I just looked over the November 2004 Sky & Telescope, and they have an article that has quite a bit on Stephan&#39;s Qunitet.

One thing worth noting is that there is a small elliptical called NGC7320c, which has roughly the same red-shift as the others in the quintet, and does have a bridge connecting it, and there is a foreground spiral galaxy called NGC7320, which is clearly closer, and has a much smaller red-shift than the rest of the cluster.

The similarity of these names caused some confusion in my above posts.

VanderL
2004-Sep-16, 05:42 PM
Hi Antoniseb,

Thanks for the information (I&#39;ll try to get a copy of S&T), I hope I at least made clear that the spiral galaxy with the lower redshift has a tail starting at North East (turning East) and that is the reason I think the galaxy is disturbed. The connection to the other members of Stephan&#39;s Quintet is not by a visible bridge but by the supposed gravitational disturbance implied by the tail.
Furthermore the visible features of the low-redshift galaxy are similar in size and resolution as at least one of the other galaxies. This could also be interpreted as evidence that the galaxies are at equal distance.

Cheers.

antoniseb
2004-Sep-16, 05:59 PM
Originally posted by VanderL@Sep 16 2004, 05:42 PM
the visible features of the low-redshift galaxy are similar in size and resolution as at least one of the other galaxies.
The S&T article makes a clear point that the features in NGC7320 [individual stars etc] are much clearer than in the distant interacting galaxies. The lead image on page 30 makes that pretty obvious.

Guest
2004-Sep-21, 06:47 PM
Hi Antoniseb,

I haven&#39;t seen the image you refer to, so if there is a picture anywhere on the web that shows this I&#39;d be interested. Here is an article (http://www.thunderbolts.info/tpod-archive-04/tpod-current.htm) of the EU site that more or less repeats the points I made (although I didn&#39;t think the image was selectively adapted to exclude some features), adding an important new observation: a quasar in the densest of the lower right galaxy. If we take a look at the picture Fraser posted in the Story Comments, the tail of NGC 7320 is still visible and curving to the East. There is another galaxy where the tails of the two galaxies "meet", is that galaxy shown in the S&T article?
So there is more to Stephan&#39;s Quintet that adds to the redshift controversy. Maybe Travis (Rector) would like to respond to this, is there indeed such a quasar as stated in the article?

Cheers.