APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

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APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by APOD Robot » Wed Dec 09, 2015 5:13 am

Image Arp 87: Merging Galaxies from Hubble

Explanation: This dance is to the death. Along the way, as these two large galaxies duel, a cosmic bridge of stars, gas, and dust currently stretches over 75,000 light-years and joins them. The bridge itself is strong evidence that these two immense star systems have passed close to each other and experienced violent tides induced by mutual gravity. As further evidence, the face-on spiral galaxy on the right, also known as NGC 3808A, exhibits many young blue star clusters produced in a burst of star formation. The twisted edge-on spiral on the left (NGC 3808B) seems to be wrapped in the material bridging the galaxies and surrounded by a curious polar ring. Together, the system is known as Arp 87 and morphologically classified, technically, as peculiar. While such interactions are drawn out over billions of years, repeated close passages should ultimately result in the death of one galaxy in the sense that only one galaxy will eventually result. Although this scenario does look peculiar, galactic mergers are thought to be common, with Arp 87 representing a stage in this inevitable process. The Arp 87 pair are about 300 million light-years distant toward the constellation Leo. The prominent edge-on spiral at the far left appears to be a more distant background galaxy and not involved in the on-going merger.

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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by Ann » Wed Dec 09, 2015 5:25 am

I'm always happy to see a galaxy picture. Arp 87 is a golden oldie.

As a fanatic color nerd, I like today's APOD, while at the same time I prefer another version of this galactic pair. Bill Snyder's version of Arp 87 shows stronger color, which makes it easier to make educated guesses about the stellar populations in these two galaxies. For example, in Bill Snyder's version of the image NGC 3808B has an extremely bright and slightly bluish inner disk, which suggests that a burst of star formation is going on in there.

In any case, this is a fantastic pair of galaxies. I'm glad they got an APOD.

Ann

EDIT: There is no actual starburst going on in NGC 3808B at present. If there was, the galaxy would be smothered in dust, which is not the case. But the bright inner disk could be the remnant of a previous starburst.
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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by Black'95 » Wed Dec 09, 2015 1:17 pm

Wouldn't it be fantastic to see the night sky from one of these galaxies!

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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by willardfraumann » Wed Dec 09, 2015 2:27 pm

Why do galaxies merge or collide if all matter started at the same place (The Big Bang) and at the same speed? Wouldn't all matter be essentially moving away from all other matter on almost parallel but slightly divergent courses?

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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by neufer » Wed Dec 09, 2015 3:05 pm

willardfraumann wrote:
Why do galaxies merge or collide if all matter started at the same place (The Big Bang) and at the same speed? Wouldn't all matter be essentially moving away from all other matter on almost parallel but slightly divergent courses?
  • It is a gravitational result of ripples that arose in the first nonillionth of a second.
https://en.wikipedia.org/wiki/Cosmic_microwave_background#Microwave_background_observations wrote: On 21 March 2013, the European-led research team behind the Planck cosmology probe released the mission's all-sky map of the cosmic microwave background. According to the map, subtle fluctuations in temperature were imprinted on the deep sky when the cosmos was about 370,000 years old. The imprint reflects ripples that arose as early, as the existence of the universe, as the first nonillionth of a second. Apparently, these ripples gave rise to the present vast cosmic web of galaxy clusters and dark matter.
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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by Chris Peterson » Wed Dec 09, 2015 3:08 pm

Ann wrote:I'm always happy to see a galaxy picture. Arp 87 is a golden oldie.

As a fanatic color nerd, I like today's APOD, while at the same time I prefer another version of this galactic pair. Bill Snyder's version of Arp 87 shows stronger color, which makes it easier to make educated guesses about the stellar populations in these two galaxies. For example, in Bill Snyder's version of the image NGC 3808B has an extremely bright and slightly bluish inner disk, which suggests that a burst of star formation is going on in there.

In any case, this is a fantastic pair of galaxies. I'm glad they got an APOD.

Ann

EDIT: There is no actual starburst going on in NGC 3808B at present. If there was, the galaxy would be smothered in dust, which is not the case. But the bright inner disk could be the remnant of a previous starburst.
But a word to the warning. Both color and brightness are determined by processing. Scientifically, we can look at the raw image data, consider the properties of the specific filters used and the photometric intensities collected by each, and make conclusions about the temperature of stars. But it is generally a mistake to look at a single color image and attempt to make any rigorous analysis of things like star formation from just the brightness and color. The two images you discuss show how differently the same object can be portrayed.
Chris

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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by khbynum » Wed Dec 09, 2015 4:24 pm

What's the spiky red object north of NGC 3808B? I'd say a nearby star, except that it doesn't look round and seems to be leaving a faint trail in the 2 o'clock direction!

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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by Astrofan » Wed Dec 09, 2015 4:42 pm

The image is not of a close pass, but rather an ejection event, whereby the galaxy on the left has been ejected by the other, as suggested by the trailing gas and dust lanes. Fully recognized that many will object to this interpretation...but the photographic evidence better fits this interpretation-here and in many other "peculiar" galaxies.

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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by Chris Peterson » Wed Dec 09, 2015 5:04 pm

Astrofan wrote:The image is not of a close pass, but rather an ejection event, whereby the galaxy on the left has been ejected by the other, as suggested by the trailing gas and dust lanes. Fully recognized that many will object to this interpretation...but the photographic evidence better fits this interpretation-here and in many other "peculiar" galaxies.
I think that numerical simulations of such systems argue otherwise.
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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by Ann » Wed Dec 09, 2015 5:37 pm

khbynum wrote:What's the spiky red object north of NGC 3808B? I'd say a nearby star, except that it doesn't look round and seems to be leaving a faint trail in the 2 o'clock direction!
The spiky red object north of NGC 3808B is indeed a foreground star. Only (sufficiently bright) foreground stars, as well as (sufficiently bright) blazars and other brilliantly bright galactic nuclei have this kind of spiky appearance in Hubble pictures. Only light sources that are not only bright but also extremely concentrated get this kind of spiky look in Hubble images (and in many other images as well). Typical galaxies never look like that. All typical galaxies are "spread out", so that their surface brightness is low.

At left you can see NGC 4921, a galaxy whose surface brightness is even lower than it is in most galaxies. But really, virtually all galaxies have low surface brightnesses. After all, you can go outside and take a look at the Milky Way if the sky above you is dark. Does the Milky Way look brilliantly bright to you? Probably not. And yet we see it edge on, which is an orientation that enhances the apparent brightness of a galaxy.

Ann
Last edited by Ann on Thu Dec 10, 2015 1:22 am, edited 1 time in total.
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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by Ron-Astro Pharmacist » Wed Dec 09, 2015 6:15 pm

Considering that both of these galaxies were in motion it's curious that the galaxy on the left seemed to have retained more material and remained uninfluenced than the right hand galaxy - NGC 3808A. Maybe it's just because we are viewing it from our perspective and not able to see it from other vantage points. NGC 3808B is less massive I believe.
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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by Chris Peterson » Wed Dec 09, 2015 6:52 pm

Ron-Astro Pharmacist wrote:Considering that both of these galaxies were in motion it's curious that the galaxy on the left seemed to have retained more material and remained uninfluenced than the right hand galaxy - NGC 3808A. Maybe it's just because we are viewing it from our perspective and not able to see it from other vantage points. NGC 3808B is less massive I believe.
It could well be perspective. The material dragged out of the plane of a galaxy is a lot more obvious when seen from the side, as on the left. There could be a similar amount of material on the right, and we just don't notice it against the much brighter background galaxy.
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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by Ron-Astro Pharmacist » Wed Dec 09, 2015 8:29 pm

Chris Peterson wrote:
Ron-Astro Pharmacist wrote:Considering that both of these galaxies were in motion it's curious that the galaxy on the left seemed to have retained more material and remained uninfluenced than the right hand galaxy - NGC 3808A. Maybe it's just because we are viewing it from our perspective and not able to see it from other vantage points. NGC 3808B is less massive I believe.
It could well be perspective. The material dragged out of the plane of a galaxy is a lot more obvious when seen from the side, as on the left. There could be a similar amount of material on the right, and we just don't notice it against the much brighter background galaxy.
Thanks Chris. These are very interesting objects that some pretty well-known astronomers have studied.
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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by MarkBour » Thu Dec 10, 2015 12:06 am

In my opinion, we see quite a bit of disturbance of both galaxies.

I do wonder why the notion of "death" was put in the caption. When two galaxies merge into one, it's a marriage, not a funeral. Indeed, a very fruitful marriage; there is lots of offspring visible already, and surely more to come. And the level of mixing of "genetic" material one has from such a process is probably far more thorough than what one gets from a simple chromosome exchange.
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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by Chris Peterson » Thu Dec 10, 2015 12:29 am

MarkBour wrote:I do wonder why the notion of "death" was put in the caption.
A lot of material gets flung out into intergalactic space, too.

How would you describe things if you got very sick, and they saved you by cannibalizing all your wife's organs to get you working again? A death or a disturbance? <g>
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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by Alohascope » Thu Dec 10, 2015 1:23 am

Special.

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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by MarkBour » Thu Dec 10, 2015 5:44 pm

Chris Peterson wrote:A lot of material gets flung out into intergalactic space, too.
Ah. Watching simulations (never yet built or borrowed one myself), I hadn't realized that.
I wonder what is typical for the masses: 1 + 1 => 1.??
How would you describe things if you got very sick, and they saved you by cannibalizing all your wife's organs to get you working again? A death or a disturbance?
I suppose especially, if I did the cannibalization ... I would say that would be death and murder.

Unless we ended up with two functioning brains in the result. Then it would be something else. Perhaps like Ovid's Salmacis and Hermaphroditus. :o
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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by Pianosorplanets » Fri Dec 11, 2015 8:32 am

Since I seem to be the only one who sees this, I'm likely about to speak out of one of my lesser orifices.

But: By following the dust trails carefully as well as what is left of the spirals, I find no good reason to classify this as an interaction between two galaxies. Unless the spectroscopy declares me a liar, I perceive three galaxies all interacting in this stellar area.

I will use "vertical" since I don't know where north is:
Three galaxies would explain why the dust trails in NGC 3808B present clearly perpendicular forms wound independently in conjunction with perpendicular remains of stellar arm residue. Following the residue associated with the vertical object also seems to account for the bulk of the stellar matter composing the bridge.

Does anyone care to cast more light (no pun intended) on the matter? I'm no astrophysicist and am quite content to be told why I'm incorrect.
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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by geckzilla » Fri Dec 11, 2015 9:31 am

Pianosorplanets wrote:Does anyone care to cast more light (no pun intended) on the matter? I'm no astrophysicist and am quite content to be told why I'm incorrect.
You don't have to be an astrophysicist to see the galaxies are interacting. I'm not one, but I've seen enough spiral galaxies to say that both are disturbed. I've also seen enough interacting galaxies to say that these are both probably in an early stage of interaction, perhaps even on their first pass next to one another, given that they still both largely retain their spiral structures. A better way to ask your question might be, if they are not interacting, how does one explain their shapes otherwise? The answer to that is probably far more complex and unlikely than interaction. As for certain parts such as the bar and inner spiral not being disturbed yet, you might try to imagine what's in store for them in the future. It makes sense that the more loosely bound stars are more easily stirred from their positions than those denser structures such as the bar or those proximal to the nucleus.
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Re: APOD: Arp 87: Merging Galaxies from Hubble (2015 Dec 09)

Post by tarzan » Fri Jan 01, 2016 7:09 am

No one has yet mentioned the alternative explanation of a fission process
producing two or more objects in a system.
The term "merger" has been used as a "working hypothesis" so why can't 'fission'
be an alternative scenario as well as the appropriate theoretical one?
Come have a look at the DECaLS survey images at zoo.inc's citizen science site.
One can link to Skyserver and view fields full of systems with many redshift-paired
objects eg.,
http://www.galaxyzoo.org/#/examine/AGZ000ao9d z.060 .061 FCs
http://www.galaxyzoo.org/#/examine/AGZ000aykr z.061 .062
http://www.galaxyzoo.org/#/examine/AGZ000bf7m z.062s & .063s
http://www.galaxyzoo.org/#/examine/AGZ000arp6 z.067s SW
http://www.galaxyzoo.org/#/examine/AGZ000b54t z.068s edge-on south

http://www.galaxyzoo.org/#/examine/AGZ000alkw z.075 .072
http://www.galaxyzoo.org/#/examine/AGZ000bgud z.076 .077 .078 NED

http://www.galaxyzoo.org/#/examine/AGZ000auu0 z.084 .086
http://www.galaxyzoo.org/#/examine/AGZ000ax0x z.085 .087 .088
http://www.galaxyzoo.org/#/examine/AGZ000baq1 z.087 .088
* FC denotes Field Companion(s)

790 fission system 'pairs' have been analyzed and there are about 3000 being
processed. It is hoped that ~ 10000 will be identified by 2017.

Happy New Year everyone!