APOD: Stephan's Quintet (2012 Feb 25)

[APOD Robot]

Stephan's Quintet

Explanation: The first identified compact galaxy group, Stephan's Quintet is featured in this eye-catching image constructed with data drawn from the extensive Hubble Legacy Archive. About 300 million light-years away, only four of these five galaxies are actually locked in a cosmic dance of repeated close encounters. The odd man out is easy to spot, though. The interacting galaxies, NGC 7319, 7318A, 7318B, and 7317 have an overall yellowish cast. They also tend to have distorted loops and tails, grown under the influence of disruptive gravitational tides. But the predominantly bluish galaxy, NGC 7320, is closer, just 40 million light-years distant, and isn't part of the interacting group. Stephan's Quintet lies within the boundaries of the high flying constellation Pegasus. At the estimated distance of the quartet of interacting galaxies, this field of view spans about 500,000 light-years. However, moving just beyond this field, above and to the left, astronomers can identify another galaxy, NGC 7320C, that is also 300 million light-years distant. Of course, including it would bring the interacting quartet back up to quintet status.

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[Ann]

Stephan's Quintet is of course an old favorite, but it deserves being shown again. Besides, this processed version of the Hubble data is probably brand new.

Stephan's Quintet was very controversial a few decades ago, when Halton Arp used this galaxy group to argue that the idea of cosmological redshift must be wrong. Arp argued that all the galaxies in Stephan's Quintet, including bluish foreground galaxy NGC 7320, were interacting with each other and therefore at the same distance. But the redshift of NGC 7320 is completely different from the redshifts of the other galaxies. Arp argued that the galaxies were at the same distance and the redshifts must be wrong, but modern astronomy says that the redshifts are correct and the galaxies are at different distances.

Back in the days of Halton Arp, astrophotography wasn't good enough to bring out many details in Stephan's Quintet. These days Hubble can resolve the galaxy group well enough to clearly demonstrate that NGC 7320 is a very different beast than the other four galaxies. NGC 7320 has a small faint bulge and a small faint nucleus, whereas the other galaxies have large yellow bulges which are so bright that we can't even see their nuclei in today's APOD. (Hubble is of course able to see their nuclei, but a shorter exposure is needed top bring down the brightness of the bulges and bring out the nuclei. Or else, possibly, a different processing of the Hubble data is needed.)

NGC 7320 has also got a bluish disk which looks very grainy in today's APOD. We can see many small clusters, and we may possibly see some individual stars. In fact, we probably do, in view of the fact that there are several faint orange points scattered over the face of NGC 7320. They are probably red giants or supergiants.

The other galaxies, particularly NGC 7318B, have thrown out incredible tidal features which are full of considerably more course-looking blue or blue-green clumps. These are huge clusters and nebulae. There is a lot less graininess in the blue parts of NGC 7318A and B and NGC 7319 than there is in NGC 7320, because at their distance Hubble can't resolve large numbers of small clusters.

In other words, Hubble has given us clear proof that NGC 7320 is a foreground galaxy. Personally I think NGC 7320 resembles nearby dwarf galaxy NGC 300. (The picture is by J-P Metsävainio.) According to Principal Galaxy Catalog, NGC 300 is about 8.5 million light-years away and about 0.2 as bright as the Milky Way, but according to http://en.wikipedia.org/wiki/NGC_300 NGC 300 is about 6 million light-years away, which would make it even smaller. NGC 300 is a dwarf galaxy, and so is NGC 7320.

This GALEX ultraviolet image shows relatively nearby spiral galaxy NGC 7331 at upper right and Stephan's Quintet at lower left. NGC 7320 is the undisturbed-looking oval there. It could be that NGC 7320 is a satellite galaxy of NGC 7331, or at least that they belong to their own "Local Group".

Ann

[Psnarf]

Upon closer inspection of the full-size image, I'm pretty-much convinced that if you follow a path far enough from Earth through any aribitrary point in the celestial sphere, you'll eventually encounter a galaxy.

[Chris Peterson]

Upon closer inspection of the full-size image, I'm pretty-much convinced that if you follow a path far enough from Earth through any aribitrary point in the celestial sphere, you'll eventually encounter a galaxy.

I think the probability of any arbitrary point in the sky lying in a galaxy is pretty low, meaning that (if we restrict ourselves to the observable Universe, and travel no further than 46 billion light years) we are unlikely to pass through any galaxies.

[neufer]

Upon closer inspection of the full-size image, I'm pretty-much convinced that if you follow a path far enough from Earth through any aribitrary point in the celestial sphere, you'll eventually encounter a galaxy.

I think the probability of any arbitrary point in the sky lying in a galaxy is pretty low, meaning that (if we restrict ourselves to the observable Universe, and travel no further than 46 billion light years) we are unlikely to pass through any galaxies.

[c]It can't be Olber stated. [/c]

[neufer]

Click to play embedded YouTube video.

__ 8-micrometre infrared light = red,
H-alpha = green, visible red light = blue

[Ann]

Art wrote:

It can't be Olber stated.

Yup. http://en.wikipedia.org/wiki/Olbers'_paradox.

Ann

[Chris Peterson]

Art wrote:

It can't be Olber stated.

Yup. http://en.wikipedia.org/wiki/Olbers'_paradox.

Ann

Which of course isn't a paradox at all (I don't think any physical phenomena are... true paradoxes are reserved for mathematics).

[alphachapmtl]

Upon closer inspection of the full-size image, I'm pretty-much convinced that if you follow a path far enough from Earth through any aribitrary point in the celestial sphere, you'll eventually encounter a galaxy.

Specially the further we go the more packed are the galaxies, since older universe was smaller.

[alphachapmtl]

Click to play embedded YouTube video.

__ 8-micrometre infrared light = red,
H-alpha = green, visible red light = blue

At first the galaxies at 2:08 in the movie looks different, but you're right! It is Stephan's Quintet! Good find!
http://paulandliz.org/Galaxies/Galaxies_Clusters.htm

http://tinypic.com/r/m81ohs/5
http://i41.tinypic.com/m81ohs.jpg

[Chris Peterson]

Specially the further we go the more packed are the galaxies, since older universe was smaller.

The further we go, the farther apart the galaxies are, because they've had more time to expand. With a telescope we see old photons, but we never see a densely packed Universe. Pick a spot at random on the sky, and the odds are that nothing will be there but the Big Bang itself, seen as a 3K photon.

[Ann]

Thanks, alphachapmtl, for translating the neufer-ese for me! You're right, it is Stephan's Quintet!

So in that Capra movie, God is NGC 7318 A and 7318 B!

Ann

[neufer]

Thanks, alphachapmtl, for translating the neufer-ese for me!

Say, brainless...I've been nominated for membership in the National Geographic Society

[Beyond]

Thanks, alphachapmtl, for translating the neufer-ese for me!

Say, brainless...I've been nominated for membership in the National Geographic Society

Hey, great happening, neufer, but what do they have to do with space? Last i knew, they are earthers, and only see stars if they get run over in a stampede or something similar.

[neufer]

I've been nominated for membership in the National Geographic Society

Hey, great happening, neufer, but what do they have to do with space?
Last i knew, they are earthers, and only see stars if they get run over in a stampede or something similar.

http://ngm.nationalgeographic.com/ngm/space/

[Beyond]

ha-ha-ha, hey, when did NG get involved with space stuff? I guess they finally ran out of things to document down here. Well, if The National Honor Society that i was inducted into many a year ago, ever goes the space route also, then i'm all set already.

[jinger]

the wikipedia graphic for Olbers' paradox gives new meaning to Orange Crush

[neufer]

I'm pretty-much convinced that if you follow a path far enough from Earth through any aribitrary point in the celestial sphere, you'll eventually encounter a galaxy.

I think the probability of any arbitrary point in the sky lying in a galaxy is pretty low, meaning that (if we restrict ourselves to the observable Universe, and travel no further than 46 billion light years) we are unlikely to pass through any galaxies.

• If we travel further than 31 billion light years we are unlikely to pass through any galaxies.

[b][color=#0000FF]EGSY8p7 (Hubble and Spitzer, space telescopes)[/color][/b]

---

<<EGSY8p7 is a distant galaxy, with a spectroscopic redshift of z = 8.68 (~30.44 Gly distant), a light travel distance of 13.2 billion light-years from Earth and observed as it existed 570 million years after the Big Bang. In July 2015, EGSY8p7 was announced as the oldest and most-distant known object.

The light of the EGSY8p7 galaxy appears to have been magnified twofold by gravitational lensing in the light's travel to Earth, enabling detecting EGSY8p7, which would not have been possible without the magnification. EGSY8p7's distance from Earth was determined by measuring the redshift of Lyman-alpha emissions. EGSY8p7 is the most distant known detection of hydrogen's Lyman-alpha emissions. The distance of this detection was surprising, because neutral hydrogen (atomic hydrogen) clouds filling the early universe should have absorbed these emissions, even by some hydrogen cloud sources closer to Earth, according to the standard cosmological model. A possible explanation for the detection would be that reionization progressed in a "patchy" manner, rather than homogeneously throughout the universe, creating patches where the EGSY8p7 hydrogen Lyman-alpha emissions could travel to Earth, because there were no neutral hydrogen clouds to absorb the emissions.>>

Were the succession of stars endless, then the background of the sky would present us an uniform luminosity, like that displayed by the Galaxy -- since there could be absolutely no point, in all that background, at which would not exist a star. The only mode, therefore, in which, under such a state of affairs, we could comprehend the voids which our telescopes find in innumerable directions, would be by supposing the distance of the invisible background so immense that no ray from it has yet been able to reach us at all.

- Edgar Allan Poe, Eureka: A Prose Poem (1848)

<<Eureka (1848) is a lengthy non-fiction work by American author Edgar Allan Poe (1809–1849) which he subtitled "A Prose Poem", though it has also been subtitled as "An Essay on the Material and Spiritual Universe". Adapted from a lecture he had presented, Eureka describes Poe's intuitive conception of the nature of the universe with no antecedent scientific work done to reach his conclusions. Though it is generally considered a literary work, some of Poe's ideas anticipate 20th century scientific discoveries and theories.

Poe's work presages modern science with his own concept of the Big Bang.[32][33] He postulated that the universe began from a single originating particle or singularity[which] divides into all the particles of the universe. These particles seek one another because of their originating unity (gravity) resulting in the end of the universe as a single particle. Poe also expresses a cosmological theory that anticipated black holes and the Big Crunch theory as well as the first plausible solution to Olbers' paradox (the night sky is dark despite the vast number of stars in the universe). In 1987 astronomer Edward Robert Harrison published a book, Darkness at Night, on this paradox. This book clarified why lack of energy explains the paradox, and lays out how Harrison discovered that Poe's Eureka anticipated this conclusion.

Eureka was received poorly in Poe's day and generally described as absurd, even by friends. Modern critics continue to debate the significance of Eureka and some doubt its seriousness, in part because of Poe's many incorrect assumptions and his comedic descriptions of well-known historical minds. He considered it his greatest work and claimed it was more important than the discovery of gravity.>

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