APOD: Stephan's Quintet from Hubble (2019 Jun 03)

[APOD Robot]

Stephan's Quintet from Hubble

Explanation: When did these big galaxies first begin to dance? Really only four of the five of Stephan's Quintet are locked in a cosmic tango of repeated close encounters taking place some 300 million light-years away. The odd galaxy out is easy to spot in this recently reprocessed image by the Hubble Space Telescope -- the interacting galaxies, NGC 7319, 7318B, 7318A, and 7317 (left to right), have a more dominant yellowish cast. They also tend to have distorted loops and tails, grown under the influence of disruptive gravitational tides. The mostly bluish galaxy, large NGC 7320 on the lower left, is in the foreground at about 40 million light-years distant, and so is not part of the interacting group. Data and modeling indicate that NGC 7318B is a relatively new intruder. A recently-discovered halo of old red stars surrounding Stephan's Quintet indicate that at least some of these galaxies started tangling over a billion years. Stephan's Quintet is visible with a moderate sized-telescope toward the constellation of Winged Horse (Pegasus).

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[Ann]

This picture demonstrates perfectly why we can tell at a (Hubble) glance that one member of this particular galaxy group is a foreground interloper.

Look at the extremely speckled, spotted disk of NGC 7320. We can many individual stars all over its disk, almost like grains of sand. The bulge of NGC 7320 is small, faint and barely yellow. There is a tiny, apparently not very bright nucleus in the center of the bulge.

The other galaxies have large, brilliant yellow bulges with brilliant white cores. (Well, maybe not so much NGC 7319.) The blue objects that are associated with the other galaxies are in most cases huge star clusters and giant nebulas.

NGC 7320 appears to be the same size as the other galaxies. In reality, though, NGC 7320 is a nearby dwarf galaxy, while the other four are giants caught in a titanic battle.

Ann

[C Downunder]

I want to ask about the estimate stellar mass of NGC7320 vs the other more distant galaxies. (If known.)

The more distant colliding spiral galaxies are about the same angular size as NGC7320, even though much more distant. Given the ratio of distances is 300/40 (Million LY) to my understanding then the farther galaxies must be about 7 times larger in diameter. Wondering what that translates to in regard to their respective stellar masses. (If known.) I take it diameter of a galaxy of similar shape vs total stellar mass is not a linear relationship.

The question arises as an exercise in getting my mind around the scale of galaxies that, even though they are hugely different mass systems, they evolve such similar morphological form as spirals (before collision). That is quite remarkable in regards to the consistency of the outcomes from the underlying physical dynamics.

It also raises the question to my mind if there is a lower stellar mass limit to a galaxy where in it will not develop a spiral structure.

[Iksarfighter]

Hey,
Where can I find better resolution of this image pls ?

[Ann]

I want to ask about the estimate stellar mass of NGC7320 vs the other more distant galaxies. (If known.)

The more distant colliding spiral galaxies are about the same angular size as NGC7320, even though much more distant. Given the ratio of distances is 300/40 (Million LY) to my understanding then the farther galaxies must be about 7 times larger in diameter. Wondering what that translates to in regard to their respective stellar masses. (If known.) I take it diameter of a galaxy of similar shape vs total stellar mass is not a linear relationship.

The question arises as an exercise in getting my mind around the scale of galaxies that, even though they are hugely different mass systems, they evolve such similar morphological form as spirals (before collision). That is quite remarkable in regards to the consistency of the outcomes from the underlying physical dynamics.

It also raises the question to my mind if there is a lower stellar mass limit to a galaxy where in it will not develop a spiral structure.

I can't give any sort of estimate, but I can tell you that most of the mass in almost all galaxies is concentrated in their bulges. (Unless for some reasons there is a huge mass of dark matter in their haloes.)

Let's go for the idea that most of the mass is concentrated in the bulges of galaxies, and that most of the mass in the bulge is in the form of baryonic (not dark) matter. Given this assumption, you can tell at a glance that NGC 7320 must contain much less mass in its bulge than the other galaxies. The sheer faintness of the bulge of NGC 7320 is ample proof of that.

So NGC 7320 is not just smaller than the other galaxies, but it also contains a lot less matter than the others for every unit of its volume, out to a certain distance from the center of the galaxy. Unless, again, dark matter is playing tricks on us. (And unless it doesn't possess a truly huge low-luminosity halo.)

Click to view full size image

Malin 1.
HST (NASA/ESA), STScI/ST-ECF/CADC

Wikipedia wrote:

Malin 1 is a giant low surface brightness (LSB) spiral galaxy.[1][8] It is located 1.19 billion light-years (366 Mpc) away in the constellation Coma Berenices, near the North Galactic Pole. As of February 2015, it is arguably the largest known spiral galaxy, with an approximate diameter of 650,000 light-years (200,000 pc),[5][6][7] thus over three times the diameter of our Milky Way. It was discovered by astronomer David Malin in 1986 and is the first LSB galaxy verified to exist.[8][7][5] Its high surface brightness central spiral is 30,000 light-years (9,200 pc) across, with a bulge of 10,000 light-years (3,100 pc).[5] The central spiral is a SB0a type barred-spiral.[5]

Malin 1 is peculiar in several ways: its diameter alone would make it the largest barred spiral galaxy ever to have been observed.[4]

So Malin 1 might look like a small galaxy to us, because its high surface brightness inner part is only a third of the size of the Milky Way (or, if you count the apparent size of the bright two-dimensional surface of Malin 1, it is much smaller still compared with the Milky Way). But in reality, its low surface brightness outer parts makes it at least three times bigger than the Milky Way, and much bigger still if you think of it as a flattened disk, and much bigger still if you think of it as a spherical halo.

Ann

[C Downunder]

Ann, thank you for such a considered response. Very much valued.

The Malin 1 galaxy would seem to be the upper limit. 650,000 light years diameter is staggering. Your information and direction helps me with gaining a sense of scale of the mass range for spiral galaxies. Thank you so much for that.

[BDanielMayfield]

Let's go for the idea that most of the mass is concentrated in the bulges of galaxies, and that most of the mass in the bulge is in the form of baryonic (not dark) matter. Given this assumption...

Sorry Ann, but that's not a likely assumption, since dark matter out weighs baryonic by about three to one. Going just by appearance alone can lead to wrong conclusions, since there is usually much more that is unseen than that which is seen.

Bruce

[orin stepanek]

Beautiful set of galaxies! Thanks APOD; for letting us visit!

[BDanielMayfield]

Let's go for the idea that most of the mass is concentrated in the bulges of galaxies, and that most of the mass in the bulge is in the form of baryonic (not dark) matter. Given this assumption...

Sorry Ann, but that's not a likely assumption, since dark matter out weighs baryonic by about three to one. Going just by appearance alone can lead to wrong conclusions, since there is usually much more that is unseen than that which is seen.

Bruce

Correction: Dark matter to normal matter ratio is even larger than I remembered: 85:15 or about 5.7 to 1!

[Chris Peterson]

Let's go for the idea that most of the mass is concentrated in the bulges of galaxies, and that most of the mass in the bulge is in the form of baryonic (not dark) matter. Given this assumption...

Sorry Ann, but that's not a likely assumption, since dark matter out weighs baryonic by about three to one. Going just by appearance alone can lead to wrong conclusions, since there is usually much more that is unseen than that which is seen.

Right. The mass of virtually all galaxies is dominated by dark matter. But the total mass can still be estimated by measuring the luminous mass, most of which exists in the bulge (with disc galaxies).

[C Downunder]

Bruce,

Sorry Ann, but that's not a likely assumption, since dark matter out weighs baryonic by about three to one. Going just by appearance alone can lead to wrong conclusions, since there is usually much more that is unseen than that which is seen.

Thanks for that. Good point.

With today's APOD, and reading the explanation, things jarred a little in my head with - how does that add up. How can the 7 times more distant galaxies appear the same apparent size. Twice as distant maybe, but 7 times. Surely not!

I have not been able to find an estimate of the width of the closer galaxy NGC 7320 nor its estimate stellar mass, but given the information from Ann that:
- the Malin 1 galaxy is 650,000 LY wide,
- the milky way as a moderate sized spiral galaxy and is around 150,000 to 200,000 LY wide,
- then the closer NGC 7320 galaxy described as a small spiral can clearly be below 100,000 LY wide. Say 50,000 LY wide as a small galaxy.
Hence with the distance between NGC 7320 and the more distant merging galaxies being around 7 times, all the number can and do make sense to me now, provided these more distant merging spiral galaxies are in the upper limit of size towards that of Malin 1.

In terms of my original question to Ann, and your point about dark matter (3 to 1 or 5.7 to 1), this more significant dark matter mass would still likely be proportion very approximately to baryonic visible mass. Hence in terms of me seeking some sense of the scale in size of smallest to largest spiral galaxies as a ratio, as was inspired from the juxtaposition of galaxies in todays APOD, all good I think. I had no idea the scale for spiral galaxies in size (diameter) was so wide ranging.

So Ann's response did resolve the scale question in my head that I was seeking an answer to.

As for your mention of dark matter, the fact these galaxies are all colliding suggests they are likely at the centre of a galaxy cluster. This being so, then density and total mass of dark matter, as you raise, is likely to be higher than in the closer galaxy which is out on its own in free space. Hence if the question were: "How do the masses compare", rather than how do the diameters compare, then I think your point of dark matter would be very relevant. Or perhaps that should be: "What is the comparison of the size of the two gravity wells involved here." Definitely relevant.

[tomatoherd]

There colors in this view are so vivid it reminds me of those overly painted or dyed flowers at the grocery store. Yuck.

[C Downunder]

Ann 4725 Angstroms? Hydrogen, Helium, Cerium, Molybdenum, Rhenium, Tungsten, Yttrium? Neon?

[De58te]

I don't see where you get this talk of 7 times larger. If these Stephan's Quintets are 300 million ly away and the galaxy in front is 40 million ly away and they appear the same size than the former are 260 million light years farther away than the latter. So if they were all 40 million ly away the Quintets would be 6.5 times bigger. 40 times 6.5 = 260. If NGC 7320 is about 30,000 ly wide (as I found on the web) then the Quintets are some 200,000 ly wide or about the size of the Andromeda Galaxy. If you allow NGC 7320 to be 50,000 ly wide than they are about 60% larger than Andromeda.

[Psnarf]

Iksarfighter:

https://upload.wikimedia.org/wikipedia/ ... 9.full.jpg

[bystander]

Where can I find better resolution of this image pls ?

... this recently reprocessed image ...

Data as originally processed by the Hubble SM4 ERO Team can be found at ESA Hubble and HubbleSite.

[Locutus76]

Great image! I always check out the links in the description, but sadly one of them (2nd Stephan’s Quintet) leads to a paywall at Nature.com

[Ann]

Let's go for the idea that most of the mass is concentrated in the bulges of galaxies, and that most of the mass in the bulge is in the form of baryonic (not dark) matter. Given this assumption...

Sorry Ann, but that's not a likely assumption, since dark matter out weighs baryonic by about three to one. Going just by appearance alone can lead to wrong conclusions, since there is usually much more that is unseen than that which is seen.

Bruce

Click to view full size image

Stephan's Quintet in SDDS r-band, GALEX FUV, VLA radio, XMM NEWTON soft X-ray.
Lower row: SPITZER IRAC 8μm and MIPS 24,70,160μm.
Source: http://inspirehep.net/record/871823?ln=en

The reason why I think that NGC 7320 is not an extreme galaxy when it comes to dark matter is that it has been photographed many times through different wavelengths, precisely because it is seen right in front of the interacting members of Stephan's Quintet. The row of pictures at right is just one example.

Click to view full size image

NGC 4625 (top) and NGC 4618.
Photo: GALEX.

To see what I mean about hidden features that are revealed through multi-wavelength photography, look at the pair of galaxies at left, NGC 4625 (top) and NGC 4618. The luminous inner disks of the galaxies are their optically bright parts. But as you can see, NGC 4625 is surrounded by an extended disk of faint arm fragments. These outer arms glow in ultraviolet light, due to the fact that hot stars have formed in them. We have to assume that this star formation is very recent and that NGC 4625 has not had time to build the rich stellar populations that would make these arms optically bright.

The ultraviolet-bright arms of NGC 4625 were revealed by NASA's ultraviolet-detecting space telescope GALEX. (Interestingly enough, you can just make out the arms of NGC 4625 in this RGB picture by Tom Bash and John Fox/Adam Block/NOAO/AURA/NSF.)

Click to view full size image

Hydrogen halos around NGC 4625 and NGC 4618.
The image is composed of ultraviolet, visible-light and radio data, from
the Galaxy Evolution Explorer, the California Institute of Technology's Digitized
Sky Survey, and the Westerbork Synthesis Radio Telescope, the Netherlands,
respectively. Near-ultraviolet light is colored green;
far-ultraviolet light is colored blue; and optical light is colored red.
Radio emissions are colored purple.

When the outer arms of NGC 4625 were discovered, NGC 4618 and NGC 4625 were photographed at radio wavelengths to detect any cool hydrogen gas surrounding NGC 4625, which might explain how this galaxy suddenly started making outer arms. Hydrogen halos were detected around both NGC 4618 and NGC 4625. For some reason, only NGC 4625 has turned some of its surrounding hydrogen into an extensive set of outer arms. My point is that the more you photograph a galaxy through different wavelengths, the more you are going to discover.


To return to NGC 7320, the foreground galaxy in Stephan's Quintet, my point is that nothing unusual has ever been discovered in NGC 7320 despite extensive multi-wavelength photography. But wouldn't a massive pure dark matter halo have gone undetected? I think not. If NGC 7320 had been extremely massive for its size, wouldn't astronomers have detected its surprisingly large gravitational distortion of the images of the galaxies behind it? If you go to this page, you can click on the top image there and enlarge it. There are some very distant background galaxies seen in and very near NGC 7320's luminous disk. Wouldn't we have seen som gravitational distortion of these galaxies, if NGC 7320 had been so very massive? And wouldn't the appearance other members of Stephan's Quintet have been affected by a huge mass concentration in NGC 7320?

Ann

[Ann]

I have not been able to find an estimate of the width of the closer galaxy NGC 7320 nor its estimate stellar mass, but given the information from Ann that:
- the Malin 1 galaxy is 650,000 LY wide,
- the milky way as a moderate sized spiral galaxy and is around 150,000 to 200,000 LY wide,
- then the closer NGC 7320 galaxy described as a small spiral can clearly be below 100,000 LY wide. Say 50,000 LY wide as a small galaxy.
Hence with the distance between NGC 7320 and the more distant merging galaxies being around 7 times, all the number can and do make sense to me now, provided these more distant merging spiral galaxies are in the upper limit of size towards that of Malin 1.

In terms of my original question to Ann, and your point about dark matter (3 to 1 or 5.7 to 1), this more significant dark matter mass would still likely be proportion very approximately to baryonic visible mass. Hence in terms of me seeking some sense of the scale in size of smallest to largest spiral galaxies as a ratio, as was inspired from the juxtaposition of galaxies in todays APOD, all good I think. I had no idea the scale for spiral galaxies in size (diameter) was so wide ranging.

So Ann's response did resolve the scale question in my head that I was seeking an answer to.

As for your mention of dark matter, the fact these galaxies are all colliding suggests they are likely at the centre of a galaxy cluster. This being so, then density and total mass of dark matter, as you raise, is likely to be higher than in the closer galaxy which is out on its own in free space. Hence if the question were: "How do the masses compare", rather than how do the diameters compare, then I think your point of dark matter would be very relevant. Or perhaps that should be: "What is the comparison of the size of the two gravity wells involved here." Definitely relevant.

Anne's Astronomy wrote:
NGC 7320 (also known as PGC 69270) is an unbarred spiral dwarf galaxy of some 30 thousand light-years across, located about 39 million light-years away from Earth in the northern constellation of Pegasus (the Winged Horse).

I don't know where Anne's Astronomy found that size estimate for NGC 7320, but a diameter of 30 thousand light-years for a galaxy of this type seems reasonable to me.

I believe that our own Milky Way is relatively large as galaxies go. It is very, very far from being any sort of record holder, but in spite of that, it is pretty large. Most galaxies are smaller than the Milky Way.

If you go to this page, you will find pictures showing the estimated sizes of a number of galaxies. Careful, though: The size estimates are subject to considerable uncertainty.

Ann

[Ann]

Ann 4725 Angstroms? Hydrogen, Helium, Cerium, Molybdenum, Rhenium, Tungsten, Yttrium? Neon?

Naaah. I was just given that nick by the moderators, because 4725 Angstroms is blue wavelength, and I love blue things. Also the unit Angstrom was named after a Swedish scientist, and I am Swedish. Angstrom is really spelled Ångström in Swedish, and neufer, a member of Starship Asterisk, likes to call me Ånn. That is not my name!

Ann

Edit: I haven't ever asked myself why I was given the specific wavelength of 4725 Å. Now do I have to find out what exactly it means? Oh no!

Okay. Cerium has to spectral lines near 4725 Å, namely 4724.85 Å and 4725.09 Å. And Yttrium has one line at 4725.85 Å. Well, Yttrium was discovered in a Swedish mine, so maybe someone thought of that? I have no idea!

[sillyworm 2]

There's an interesting object (merging Galaxies?) at 6:00 below the background elliptical. The 2 cores
look mighty close together.

[Cliff]

why don't these three system all come together and become one?

[C Downunder]

I don't see where you get this talk of 7 times larger. If these Stephan's Quintets are 300 million ly away and the galaxy in front is 40 million ly away and they appear the same size than the former are 260 million light years farther away than the latter. So if they were all 40 million ly away the Quintets would be 6.5 times bigger. 40 times 6.5 = 260. If NGC 7320 is about 30,000 ly wide (as I found on the web) then the Quintets are some 200,000 ly wide or about the size of the Andromeda Galaxy. If you allow NGC 7320 to be 50,000 ly wide than they are about 60% larger than Andromeda.

Yes, my initial back of envelope calculations were very approximate. Yours, with better information are much better. And further, give a more accurate picture of the reality of actual size (diameter).

[C Downunder]

why don't these three system all come together and become one?

I think you will find that is exactly what they are doing ..... process taking about 1 billion years.

If you look closely, you might find that the two distant galaxies of the three on the left, are in fact two galaxies each, both in the process of merging. One has visibly one core, hence is a long way down the time line of merging, while the other with two clear cores is still on the process of merging. So while one at first perceives 3 galaxies in the distance, there are actually 5. Hence "Quintet"!

I think the below utube video is a good computer simulation comparison with observed that shows the process of spiral galaxy mergers well.
--

Click to play embedded YouTube video.

--

If I understand correctly, this is a main process by which elliptical galaxies are formed over time. From the merger of spiral galaxies just like what we are watching here.

[C Downunder]

Naaah. I was just given that nick by the moderators, because 4725 Angstroms is blue wavelength, and I love blue things.

Love it!

Deep rich blue is a beautiful color.

Speaking of which, I once worked on the same worksite as David Malin. Probably have walked passed him, possibly even talked to him. I am pretty sure he was working with the Anglo Australian Telescope back in the 1980's.

Å, Cheers from Downunder.