APOD: Seyfert's Sextet (2013 Dec 10)

[Galaxian]

For those who don't see what I'm seeing.

Click on TIGHTLY PACKED in the image description.

Thanks geckzilla, at least I now know why this keeps happening (at least the mechanics if not the mentality),

Aaaawwwww. That's so cute.

Can anyone tell, I was owned by cats?

[Chris Peterson]

Are we sure the deep-diving blue whale at centre-bottom of the group is part of the interaction? I have a feeling it, too, is background but not as far from the group as the grand face-on spiral.
According to this the blue whale component, "C", has a slightly higher red shift than the rest of the group. Could that make it as far from them as M31 is from us and thus non-interacting?
We really need a 3-d, stereoscopic view. say from 90-degrees or more from our present line of sight.
Another good candidate for FTL.
Anyway, this is a beautiful image. Thank you.

I would say that "interacting" generally means the bodies are gravitationally bound- a description that certainly includes the Milky Way and M31. Interacting to the point of tidal disruption seems like the most extreme case.

You would expect each object in a cluster like this to have slightly different redshifts, since their orbits about each other introduce a Doppler shift superimposed on the cosmological redshift of the entire cluster.

[Nitpicker]

Thesextet actually contains only four interacting galaxies, though. Near the center of this Hubble Space Telescope picture, the small face-on spiral galaxy lies in the distant background and appears only by chance aligned with the main group. Also, the prominent condensation on the upper left is likely not a separate galaxy at all, but a tidal tail of stars flung out by the galaxies' gravitational interactions.

Are we sure the deep-diving blue whale at centre-bottom of the group is part of the interaction? I have a feeling it, too, is background but not as far from the group as the grand face-on spiral.
According to this the blue whale component, "C", has a slightly higher red shift than the rest of the group. Could that make it as far from them as M31 is from us and thus non-interacting?
We really need a 3-d, stereoscopic view. say from 90-degrees or more from our present line of sight.
Another good candidate for FTL.
Anyway, this is a beautiful image. Thank you.

Component C(c) has about the same redshift as component NGC6027(b). I would think it is more likely the 5 closest components are interacting in some way, than that they are not. I'm not really sure -- I'm not an expert on how galactic interactions are defined -- but it may even be fair to say that M31 and the Milky Way are currently interacting, albeit very slightly.

[Ann]

Can't help being curious about the bright pair (perhaps a binary star pair?) to the right and slightly above center in the image. The leftmost member of the pair appears to have a slightly yellowish tint, whereas the other has a bluer tint. I'm assuming this pair is unrelated to Seyfert's Sextet, but if anyone can say more regarding what's known about the pair it would be appreciated. Thanks in advance for any enlightenment! What an exciting universe we inhabit! Never a dull moment.

Very interesting, smitty. I checked out my software, which provides a grayscale around galaxies at high magnification. Because of the grayscale, it is usually possible to say if there is supposed to be something there which is too faint to be "clickable" in the graphics provided.

Well, here's the deal: there is a distant red galaxy to the lower left of the interesting "double star". My software shows a very definite brightening at the position of the galaxy. But at the position of the double star, there is nothing. On the other hand, there is another brightening, just a little brighter and a bit elongated, to the right (not the upper right) of the position of the galaxy.

I can think of a few possibilities. But first, let's try to consider what the "real" color of the double star might be. (Or let's call it the "real apparent color", or the B-V index that we would measure is we were able to measure it.)

The double star looks quite bluish to me. But then, the galaxies in Seyfert's Sextet look quite bluish, too. However, these galaxies are certainly intrinsically yellow, since they are clearly evolved (except the "vertical" elongated one that looks grainy because it is full of young clusters, and also apart from the face-on spiral galaxy). The upper two galaxies, in particular, lack any sign of star formation, and the one on the right lacks any sign of dust. Both the upper galaxies are certainly intrinsically yellow, and yet they look quite blue. Is that a criticism? No, it is an observation, and it means that the double star, which appears to be about the same color as the galaxies, is likely also yellow.

We might possibly narrow the color index of the double star down a bit more. James D Wray provided a photo of Seyfert's Sextet in his book, The Color Atlas of Galaxies. In that book, he said that the B-V index of the entire Seyfert's Sextet is 0.91, and its U-B index is 0.32. Both values are relatively red. If we toy with the possibility that the double star is about the same color as the galaxies, then we might hazard a guess that the star is a pair of K-type dwarfs. If their color index is about 1.0, then they can hardly be M-type dwarfs, and then they can't be terribly faint. But an interesting possibility is that they might be low-metal stars, in which case they could be as faint as an M-type dwarf, yet as yellow as a K-type dwarf.

So I would like to hazard a guess that this is a wide pair of small yellow-orange stars. They are sufficiently near and sufficiently fast-moving to have moved from the position they had in the picture that was used to produce the grayscale for my software to the position they have in today's APOD.

Ann

[Galaxian]

Can't help being curious about the bright pair (perhaps a binary star pair?) to the right and slightly above center in the image. The leftmost member of the pair appears to have a slightly yellowish tint, whereas the other has a bluer tint. I'm assuming this pair is unrelated to Seyfert's Sextet, but if anyone can say more regarding what's known about the pair it would be appreciated. Thanks in advance for any enlightenment! What an exciting universe we inhabit! Never a dull moment.

That image is just full of interesting stuff. Above the central dorsal fin of the group is a bright star, just right of it is a spiral galaxy that seems to be leaving a trail of stars for no good reason. Nothing else is near it. On the other side of that bright dorsal-fin star is another spiral with a massively bright core and arms that seem to have bent at the tips, like an integral S. Just right of the spiral that is part of the group, the edge on one above Blue Whale Galaxy, are two distant spirals, one orange one deeply red. Those can't be real, intrinsic colours, can they? To the left of BWG's "chest", is something that looks vaguely like either a huge irregular or a messed-up spiral. Maybe part of the group that broke off and floated away? Or maybe two interacting grand spirals? Oh,Blue Whale Galaxy is apparently called NGC6027c and the internal, distant spiral isNGC6027d. Anyway, NGC6027d, the distant spiral, looks very much like artist impression images of a galaxy we're all quite familiar with. Ours, the Milky Way. I wonder if aliens there can see us and M31?
Everybody wave.
Would we and M31 appear to be part of "Seyferts Septet"? That would be so cool.

[Chris Peterson]

I'm not really sure -- I'm not an expert on how galactic interactions are defined -- but it may even be fair to say that M31 and the Milky Way are currently interacting, albeit very slightly.

Not slightly at all. The two are in closed orbits around each other.

[Nitpicker]

I'm not really sure -- I'm not an expert on how galactic interactions are defined -- but it may even be fair to say that M31 and the Milky Way are currently interacting, albeit very slightly.

Not slightly at all. The two are in closed orbits around each other.

Thank you. I did not know that.

[geckzilla]

The double star looks quite bluish to me. But then, the galaxies in Seyfert's Sextet look quite bluish, too. However, these galaxies are certainly intrinsically yellow, since they are clearly evolved (except the "vertical" elongated one that looks grainy because it is full of young clusters, and also apart from the face-on spiral galaxy). The upper two galaxies, in particular, lack any sign of star formation, and the one on the right lacks any sign of dust. Both the upper galaxies are certainly intrinsically yellow, and yet they look quite blue. Is that a criticism? No, it is an observation, and it means that the double star, which appears to be about the same color as the galaxies, is likely also yellow.

Since this is mine, I can post whatever images I have of it. Anytime I grab some data, the first thing I try to do after getting the FITS files and converting them to TIFF is to get all of the darkest parts of the empty space to be as close to neutral black (actually a dark gray) as possible. Without fail, this is what I am looking at by the time that is done.

Since it looks like we're viewing the picture through a ancient, yellowed piece of plastic, it's easy to see why I would make some major adjustments. Between all the filters, varying exposure times, redshifting and general mysteriousness of space I never know what an absolute color is. Can't say it's worth agonizing over.

[Galaxian]

You would expect each object in a cluster like this to have slightly different redshifts, since their orbits about each other introduce a Doppler shift superimposed on the cosmological redshift of the entire cluster.

Oh. Yes. Obviously. I forgot about roundy-roundy motions.
<Mumbles> Idiot. </mumbles>
The entire *universe* is absolutely crammed full of bits of stuff going round other bits of stuff and spinning on their own axes and I forgot.
Y'know, that is so obvious.
Once it's been pointed out.
Thanks, Chris.

[Galaxian]

The double star looks quite bluish to me. But then, the galaxies in Seyfert's Sextet look quite bluish, too. However, these galaxies are certainly intrinsically yellow, since they are clearly evolved (except the "vertical" elongated one that looks grainy because it is full of young clusters, and also apart from the face-on spiral galaxy). The upper two galaxies, in particular, lack any sign of star formation, and the one on the right lacks any sign of dust. Both the upper galaxies are certainly intrinsically yellow, and yet they look quite blue. Is that a criticism? No, it is an observation, and it means that the double star, which appears to be about the same color as the galaxies, is likely also yellow.

Since this is mine, I can post whatever images I have of it. Anytime I grab some data, the first thing I try to do after getting the FITS files and converting them to TIFF is to get all of the darkest parts of the empty space to be as close to neutral black (actually a dark gray) as possible. Without fail, this is what I am looking at by the time that is done.

Since it looks like we're viewing the picture through a ancient, yellowed piece of plastic, it's easy to see why I would make some major adjustments. Between all the filters, varying exposure times, redshifting and general mysteriousness of space I never know what an absolute color is. Can't say it's worth agonizing over.

Thank you. That is so lovely. Can I keep a copy for my wallpapery collection, please?
I notice that those two "orange" and deep red galaxies below the bright binary and right of the embedded spiral are still very different in colour from each other so it must be real, yes? Anyone have any idea why the right hand one is so much redder? More distant and bigger red-shift? Smoke in the way? Older?

[geckzilla]

Thank you. That is so lovely. Can I keep a copy for my wallpapery collection, please?
I notice that those two "orange" and deep red galaxies below the bright binary and right of the embedded spiral are still very different in colour from each other so it must be real, yes? Anyone have any idea why the right hand one is so much redder? More distant and bigger red-shift? Smoke in the way? Older?

I promise I will not send the wallpaper police after you if you download any images to your computer.

Re: Redder galaxies - the redder it is, the more light is being collected in the infrared part of the spectrum and the less light is being collected from the other two visible wavelengths. Hubble images very often use F814W which is great for seeing those more distant, reddened background galaxies.

[dwainwilder]

A bit sorry to chime in on a completely different observation regarding this day's view of Seyfert's Sextet: I notice that in this view, the face-on background galaxy, NGC 6946, looks like a rectangular collection of arms! Not apparent at all in a previous view http://apod.nasa.gov/apod/ap021004.html.

Any comments?

[geckzilla]

A bit sorry to chime in on a completely different observation regarding this day's view of Seyfert's Sextet: I notice that in this view, the face-on background galaxy, NGC 6946, looks like a rectangular collection of arms! Not apparent at all in a previous view http://apod.nasa.gov/apod/ap021004.html.

Any comments?

NGC 6946 is not visible in Seyfert's Sextet. If it were, Seyfert's Sextet would appear like a few tiny background galaxies amongst the sprawling foreground of the much larger, closer NGC 6946.

[owlice]

The 2002 October 4 photo of NGC 6946 is shown as an example of a face-on spiral galaxy; it is not an image of the spiral galaxy that is captured in the image of Seyfert's Sextet. NGC 6946 is in the constellation Cepheus; Seyfert's Sextet is in Serpens. The small spiral galaxy in the background of Seyfert's Sextet has been designated NGC 6027d.

[geckzilla]

I was trying to avoid making NGC 6027d feel bad for not even getting its own number designation in the NGC. Now look what you did. It's so sad.

[Ann]

The double star looks quite bluish to me. But then, the galaxies in Seyfert's Sextet look quite bluish, too. However, these galaxies are certainly intrinsically yellow, since they are clearly evolved (except the "vertical" elongated one that looks grainy because it is full of young clusters, and also apart from the face-on spiral galaxy). The upper two galaxies, in particular, lack any sign of star formation, and the one on the right lacks any sign of dust. Both the upper galaxies are certainly intrinsically yellow, and yet they look quite blue. Is that a criticism? No, it is an observation, and it means that the double star, which appears to be about the same color as the galaxies, is likely also yellow.

Since this is mine, I can post whatever images I have of it. Anytime I grab some data, the first thing I try to do after getting the FITS files and converting them to TIFF is to get all of the darkest parts of the empty space to be as close to neutral black (actually a dark gray) as possible. Without fail, this is what I am looking at by the time that is done.

Seyferts_Sextet_yellow.jpg

Since it looks like we're viewing the picture through a ancient, yellowed piece of plastic, it's easy to see why I would make some major adjustments. Between all the filters, varying exposure times, redshifting and general mysteriousness of space I never know what an absolute color is. Can't say it's worth agonizing over.

Please understand that my point was not to criticize the color balance of the picture you processed (very beautifully), but to have an educated guess at what the "tight pair of eyes" could be.

In the new picture you provided, the stars look quite whitish. They could be whiter in color than I would have thought. But in any case, I still find it quite likely that they are a small pair of relatively nearby stars, moving quickly through space and changing their position in relation to their Seyfert Sextet background.

Ann

[geckzilla]

Yes, you made your intentions clear in your first post. My reply was intended to give you a better idea of what you're looking at.

[Anthony Barreiro]

Are we sure the deep-diving blue whale at centre-bottom of the group is part of the interaction? I have a feeling it, too, is background but not as far from the group as the grand face-on spiral.
According to this the blue whale component, "C", has a slightly higher red shift than the rest of the group. Could that make it as far from them as M31 is from us and thus non-interacting?
We really need a 3-d, stereoscopic view. say from 90-degrees or more from our present line of sight.
Another good candidate for FTL.
Anyway, this is a beautiful image. Thank you.

M31and the Milky Way are interacting.

(Later edit: I posted this comment before I had seen a whole page worth of earlier and more informative comments. This picture has prompted a very active and wide ranging discussion!)

[Ann]

Yes, you made your intentions clear in your first post. My reply was intended to give you a better idea of what you're looking at.

Thank you for that. I appreciate it.

Ann

[starsurfer]

One of my favourite interacting galaxy groups is Copeland's Septet. Adam Block has possibly the only detailed image here: http://www.caelumobservatory.com/gallery/n3750.shtml
I would love to see a long exposure of this by either Ken Crawford or Jay GaBany!

[Ann]

One of my favourite interacting galaxy groups is Copeland's Septet. Adam Block has possibly the only detailed image here: http://www.caelumobservatory.com/gallery/n3750.shtml
I would love to see a long exposure of this by either Ken Crawford or Jay GaBany!

James D Wray has a picture of Copeland's Septet in his color Atlas of Galaxies. The only really blue and starforming galaxy in the brood of seven stands out like a sore thumb in Wray's UBV photo!

Ann

[smitty]

in any case, I still find it quite likely that they are a small pair of relatively nearby stars, moving quickly through space and changing their position in relation to their Seyfert Sextet background.

Ann

Thank you, Ann (and others), for all the interesting analysis of this image. Regarding the distance to the pair of stars, I'd mentioned in a previous post that I took the faint specular "spikes" on the two to be an indication that they are relatively nearby. Is this a reliable indicator? Often, in other apods, nearby stars in the Milky Way appear with prominent spikes. I'm not sure about all the physics involved, but it seems quite common and predictable in apod images.

[geckzilla]

Diffraction spikes are caused by any point or confined source of bright light. They are not a good indicator of distance.
http://en.wikipedia.org/wiki/Diffraction_spike

[smitty]

Thanks for the link to the Wikipedia item, geckzilla. But even the image in the Wiki item seems to contradict your statement that diffraction spikes are not a good indicator of distance. The (apparently) more nearby sources of light have spikes, whereas the seemingly more distant ones don't. Not intending to start a quarrel with you, but simply seeking clarification. I even recall reading comments in various apods about the spikes being a characteristic signature of stars in the Milky Way, which are nearer us than distant background objects.

[Chris Peterson]

Diffraction spikes are caused by any point or confined source of bright light. They are not a good indicator of distance.
http://en.wikipedia.org/wiki/Diffraction_spike

Diffraction spikes aren't a good indicator of absolute distance, but in images of galaxies, any stars showing diffraction spikes are almost certainly foreground stars in our own galaxy.