APOD: Colliding Galaxies in Stephan's Quintet (2016 Aug 10)

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APOD: Colliding Galaxies in Stephan's Quintet (2016 Aug 10)

Post by APOD Robot » Wed Aug 10, 2016 4:10 am

Image Colliding Galaxies in Stephan's Quintet

Explanation: Will either of these galaxies survive? In what might be dubbed as a semi-final round in a galactic elimination tournament, the two spirals of NGC 7318 are colliding. The featured picture was created from images taken by the Hubble Space Telescope. When galaxies crash into each other, many things may happen including gravitational distortion, gas condensing to produce new episodes of star formation, and ultimately the two galaxies combining into one. Since these two galaxies are part of Stephan's Quintet, a final round of battling galaxies will likely occur over the next few billion years with the eventual result of many scattered stars and one large galaxy. Quite possibly, the remaining galaxy will not be easily identified with any of its initial galactic components. Stephan's Quintet was the first identified galaxy group, lies about 300 million light years away, and is visible through a moderately-sized telescope toward the constellation of the Winged Horse (Pegasus).

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Ann
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Re: APOD: Colliding Galaxies in Stephan's Quintet (2016 Aug 10)

Post by Ann » Wed Aug 10, 2016 7:34 am

Stephan's Quintet. Photo:
NASA, ESA, and the Hubble SM4 ERO Team
Conventionally, astronomical images are shown north up and east to the left. Compared with that convention, today's APOD has been rotated. The image at left shows the correct orientation.

According to Wikipedia, the following filters have been used to make the image at left: 8-micrometre infrared light = red, H-alpha = green, visible red light = blue. That means that all the filters used for the image detect either red or infrared light, which might explain why the blue tidal tails of NGC 7318 seem muted.

I have to wonder if Jose Jimenez Priego has used the same "filter images" to create his APOD. The color balances of the two images are very different, which might be explained by the difficulty of using an "all-red" set of images to create a three-color image.

What both images seem to show us is that NGC 7318 consists of two bright, egg-shaped to amorphous yellow blobs mashing together and machine-gun-firing bluish shards of starforming debris in a few preferred directions. Both images seem to emphasize the hulking mass of the old yellow and red stars and the wispiness of the blue firecrackers.
Seyfert's Sextet. Photo: NASA, J. English (U. Manitoba), S. Hunsberger,
S. G. Zonak, J. Charlton, and S. C. Gallagher (PSU)
Copeland's Septet. Photo: SDSS.




















It is in fact true that most compact groups of galaxies are dominated by old red stars. At left you can see another Seyfert's group, Seyfert's Sextet. The obvious spiral in the picture is a background object. The elongated blue galaxy may belong to the group, but if so, it must be a recent addition. The other galaxies in the group have been harassing each other for (possibly) billions of years, and they have used up, heated up or expelled basically all their star making material by now. At right is a picture of another compact group of yellow galaxies, Copeland's Septet.

Seyfert's Quintet is probably unusual in that it still contains as much star formation as it does. Even so, we should expect any compact group to have converted quite a lot of its "free gas" into (mostly old) stars.

It is clear that a "recent collision" like the Antennea galaxies contains a lot more blue stars and a lot less old red stars that typical galaxies of compact groups. Here you can see the Antennae galaxies in just blue and yellow, here they are in blue, yellow and Ha, here you can see a probable RGBHa image that shows huge tidal shells of old stars, and here, finally, is a comparison between the optical and the infrared appearance of the Antennae. No matter how you look at them, the brilliance of star formation dominates the Antennae.

Stephan's Quintet is not like that, but it is still quite unusual as compact groups of galaxies go in its continuing bright and widespread star formation.

Ann
Last edited by Ann on Wed Aug 10, 2016 3:01 pm, edited 1 time in total.
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Re: APOD: Colliding Galaxies in Stephan's Quintet (2016 Aug 10)

Post by astrometbcn » Wed Aug 10, 2016 9:32 am

Hi Ann

APOD image is processed from a cut of the original color image, I have tried to highlight areas of collision between the two galaxies.

Best Regards

José

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Re: APOD: Colliding Galaxies in Stephan's Quintet (2016 Aug 10)

Post by Visual_Astronomer » Wed Aug 10, 2016 1:57 pm

The rotated image is easier to frame nicely on screen - visually through a telescope the scene will be rotated, flipped, reversed, or some combination of all three depending upon the optical path and time of day, so one gets used to mentally adjusting what one sees.

This is an amazing close-up image. I was looking at Stephan's Quintet just last week - visually it is nothing more than five tiny, faint smudges of grey.

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Re: APOD: Colliding Galaxies in Stephan's Quintet (2016 Aug 10)

Post by Chris Peterson » Wed Aug 10, 2016 2:02 pm

Visual_Astronomer wrote:The rotated image is easier to frame nicely on screen - visually through a telescope the scene will be rotated, flipped, reversed, or some combination of all three depending upon the optical path and time of day, so one gets used to mentally adjusting what one sees.
It is easier to accommodate rotation than reflection, however. While rotation for aesthetics or framing is reasonable, it is appreciated when imagers stick with the conventional north up, east left rotation. It makes it much easier to compare images, which is something we frequently do in discussion.
Chris

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Re: APOD: Colliding Galaxies in Stephan's Quintet (2016 Aug 10)

Post by Boomer12k » Wed Aug 10, 2016 4:43 pm

Just awesome....

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Re: APOD: Colliding Galaxies in Stephan's Quintet (2016 Aug 10)

Post by heehaw » Wed Aug 10, 2016 6:44 pm

Glorious!

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Re: APOD: Colliding Galaxies in Stephan's Quintet (2016 Aug 10)

Post by neufer » Wed Aug 10, 2016 6:50 pm


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Re: APOD: Colliding Galaxies in Stephan's Quintet (2016 Aug 10)

Post by p1gnone » Wed Aug 10, 2016 7:55 pm

Seeing two galactic nuclei 'close' to one another only speaks to position. The relative speed in passing has just as much to say about the amount of time until coalescence, as they may swing to highly separated yet again.