APOD: The Coma Cluster of Galaxies (2018 Mar 26)

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APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by APOD Robot » Mon Mar 26, 2018 4:06 am

Image The Coma Cluster of Galaxies

Explanation: Almost every object in the above photograph is a galaxy. The Coma Cluster of Galaxies pictured here is one of the densest clusters known - it contains thousands of galaxies. Each of these galaxies houses billions of stars - just as our own Milky Way Galaxy does. Although nearby when compared to most other clusters, light from the Coma Cluster still takes hundreds of millions of years to reach us. In fact, the Coma Cluster is so big it takes light millions of years just to go from one side to the other. Most galaxies in Coma and other clusters are ellipticals, while most galaxies outside of clusters are spirals. The nature of Coma's X-ray emission is still being investigated.

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by alter-ego » Mon Mar 26, 2018 5:02 am

The first time I saw this cluster through a 6" scope left me in awe. To this day I recall that moment.
This view measures 30' across a diagonal - the image is fully contained within a full moon span.
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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by Ann » Mon Mar 26, 2018 6:52 am

alter-ego wrote:
Mon Mar 26, 2018 5:02 am
The first time I saw this cluster through a 6" scope left me in awe. To this day I recall that moment.
This view measures 30' across a diagonal - the image is fully contained within a full moon span.
Thanks for that comment, alter-ego!

I was about to write something nasty about the shapeless appearance and yellow color of all the galaxies here. But seeing the reality of all these galaxies through a telescope, seeing them all clumped together... yes, I can imagine that it must have been stunning.

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by E Fish » Mon Mar 26, 2018 11:38 am

I wasn't aware that most galaxies in clusters are elliptical. Is there an explanation for that?

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by orin stepanek » Mon Mar 26, 2018 12:01 pm

E Fish wrote:
Mon Mar 26, 2018 11:38 am
I wasn't aware that most galaxies in clusters are elliptical. Is there an explanation for that?
I don't know if that is true for all clusters! I believe that the author was referring to the Coma Cluster! :?:
So many galaxies in this picture; yet they are so far apart! :shock:
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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by BDanielMayfield » Mon Mar 26, 2018 12:24 pm

orin stepanek wrote:
Mon Mar 26, 2018 12:01 pm
E Fish wrote:
Mon Mar 26, 2018 11:38 am
I wasn't aware that most galaxies in clusters are elliptical. Is there an explanation for that?
I don't know if that is true for all clusters! I believe that the author was referring to the Coma Cluster! :?:
So many galaxies in this picture; yet they are so far apart! :shock:
I also wondered the same question E Fish raised. The Explanation says "most galaxies in the Coma and other clusters are ellipticals," so it isn't just the Coma cluster that has this composition. Maybe large galactic clusters are mostly elliptical, while smaller clusters like our local group are not?

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by sillyworm2 » Mon Mar 26, 2018 1:17 pm

I'm assuming that most Galaxies in a Cluster become Elliptical because in an earlier time there were many more Galaxies & they merged to form Ellipticals?

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by tomatoherd » Mon Mar 26, 2018 1:27 pm

If this cluster is that dense, why do we see no gravitational lensing of background galaxies? (Or are examples off-screen to the side?)

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by neufer » Mon Mar 26, 2018 1:35 pm

sillyworm2 wrote:
Mon Mar 26, 2018 1:17 pm

I'm assuming that most Galaxies in a Cluster become Elliptical because in an earlier time there were many more Galaxies & they merged to form Ellipticals?
If elliptical galaxies is primarily composed of the merging of galaxies then it seems reasonable
that any clustering of galaxies would contain a higher percentage of ellipticals than normal.
https://en.wikipedia.org/wiki/Elliptical_galaxy#Evolution wrote:
<<It is widely accepted that the evolution of elliptical galaxies is primarily composed of the merging of smaller galaxies. If the galaxies are of similar size, the resultant galaxy will appear similar to neither of the two galaxies merging, but will instead be an elliptical galaxy. It is believed that black holes may play an important role in limiting the growth of elliptical galaxies in the early universe by inhibiting star formation.>>
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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by sunson » Mon Mar 26, 2018 2:17 pm

Are those two fuzzy galaxies closer to us? And that is why they are so fuzzy? Or what?

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by Ann » Mon Mar 26, 2018 2:44 pm

sillyworm2 wrote:
Mon Mar 26, 2018 1:17 pm
I'm assuming that most Galaxies in a Cluster become Elliptical because in an earlier time there were many more Galaxies & they merged to form Ellipticals?
It does seem as if all galaxies belonging to large galaxy clusters gradually become more and more shapeless and yellow - i.e., they turn into elliptical galaxies (or possibly lenticular galaxies, but they are equally yellow and devoid of star formation). One process through which this can happen is certainly through mergers. But there are also other ways to make galaxies shapeless and yellow.

In order to lose their ability to form stars, the galaxies in a cluster must either lose their most of their gas altogether, or else their gas must become hot and turbulent, which prevents it from forming stars.

Deceptively tranquil-looking NGC 4911,
which is falling through the Coma Cluster.
NASA, ESA, and the Hubble Heritage Team (STScI/AURA);
Acknowledgment: K. Cook (LLNL) et al.
Click to play embedded YouTube video.
A galaxy losing its gas through ram pressure.























A prime example of what is going on can be seen in the spiral galaxy NGC 4911, which, would you believe it, is actually falling into to Coma Cluster, the galaxy cluster that is the subject of today's APOD!

NGC 4911 has been captured by the great gravity of the Coma Cluster, and it is falling into it. It is falling right through the massive, hot halo of gas that surrounds the galaxies of the Coma Cluster. As NGC 4911 encounters this hot halo, its own gas is being stripped away from it in a process called ram pressure.
Huge jets emitted by the black hole of elliptical radio galaxy Hercules A.
NASA, ESA, S. Baum and C. O'Dea (RIT), R. Perley and W. Cotton (NRAO/AUI/NSF),
and the Hubble Heritage Team (STScI/AURA)
Another process by which star formation is quenched in galaxy clusters probably has to do with the enormous black holes of the largest ellipticals in the cluster. As the humongous black holes are feeding, they emit tremendous jets into the halo that surrounds the entire cluster. It is likely that the energy injected into the cluster-encompassing halo heats the gas in many or most of the constituent members of the cluster. And as their gas becomes hot and turbulent, the galaxies can't make their gas "settle down" and cool down in order to form new stars.

Whatever the exact processes, it does seem that galaxies that have long been members of massive galaxy clusters lose their ability to form new stars, and become shapeless and yellow.

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by neufer » Mon Mar 26, 2018 3:10 pm

sunson wrote:
Mon Mar 26, 2018 2:17 pm

Are those two fuzzy galaxies closer to us? And that is why they are so fuzzy? Or what?
NGC 4874 (Coma A) is the fuzzy galaxy to the right while NGC 4889 (Coma B) is the fuzzy galaxy to the left.

The star above NGC 4874 is a foreground star [HD 11288] and completely unrelated to the cluster.
https://en.wikipedia.org/wiki/NGC_4874 wrote:
<<NGC 4874 (Coma A) is a giant elliptical galaxy. It was discovered by the British astronomer Frederick William Herschel I in 1785, who catalogued it as a bright patch of nebulous feature. The second-brightest galaxy within the northern Coma Cluster, it is located at a distance of 109 megaparsecs (350 million light-years) from Earth. Unlike a disc-shaped spiral galaxy like the Milky Way, NGC 4874 has no extensive dust lanes or spiral arms and has a smooth, featureless, ball-shaped profile that diminishes in luminosity with distance from the center. The galaxy is surrounded by an immense stellar halo that extends up to one million light-years in diameter. It is also enveloped by a huge cloud of interstellar medium that is currently being heated by action of infalling material from its central supermassive black hole. A jet of highly energetic plasma extends out to 1,700 light-years from its center.>>
https://en.wikipedia.org/wiki/NGC_4889 wrote:

<<NGC 4889 (also known as Coma B) is an E4 supergiant elliptical galaxy. It was discovered in 1785 by the British astronomer Frederick William Herschel I, who catalogued it as a bright, nebulous patch. The brightest galaxy within the northern Coma Cluster, it is located at a distance of 94 million parsecs (308 million light years) from Earth. As the largest and the most massive galaxy easily visible to Earth, NGC 4889 has played an important role in both amateur and professional astronomy, and has become a prototype in studying the dynamical evolution of other supergiant elliptical galaxies in the more distant universe.Unlike a flattened, disc-shaped spiral galaxy like the Milky Way, NGC 4889 has no visible dust lanes or spiral arms and has a smooth, featureless, egg-shaped profile that diminishes in luminosity with distance from the center. At the core of the galaxy is a supermassive black hole that heats the intracluster medium through the action of friction from infalling gases and dust. The gamma ray bursts from the galaxy extend out to several million light years of the cluster.

As with other similar elliptical galaxies, only a fraction of the mass of NGC 4889 is in the form of stars. They have a flattened, unequal distribution that bulges within its edge. Between the stars is a dense interstellar medium full of heavy elements emitted by evolved stars. The diffuse stellar halo extends out to one million light years in diameter. Orbiting the galaxy is a very large population of globular clusters. NGC 4889 is also a strong source of soft X-ray, ultraviolet, and radio frequency radiation.

NGC 4889 was not included by the astronomer Charles Messier in his famous Messier catalogue despite being an intrinsically bright object quite close to some Messier objects. The first known observation of NGC 4889 was that of Frederick William Herschel I, assisted by his sister, Caroline Lucretia Herschel, in 1785, who included it in the Catalogue of Nebulae and Clusters of Stars published a year later. In 1864, Herschel's son, John Frederick William Herschel, published the General Catalogue of Nebulae and Clusters of Stars. He included the objects catalogued by his father, including the one later to be called NGC 4889, plus others he found that were somehow missed by his father.

NGC 4889 is probably the largest and the most massive galaxy out to the radius of 100 Mpc (326 million light years) of the Milky Way. The galaxy has an effective radius which extends at 2.9 arcminutes of the sky, translating it to the diameter of 239,000 light years, about the size of the Andromeda Galaxy. In addition it has an immense diffuse light halo extending to 17.8 arcminutes, roughly half the angular diameter of the Sun, translating to 1.3 million light years in diameter.

As for its large size, NGC 4889 may also be extremely massive. If we took Milky Way as the standard of mass, it may be close to 8 trillion solar masses. However, as NGC 4889 is a spheroid, and not a flat spiral, it has a three-dimensional profile, so it may be as high as 15 trillion solar masses. However, as for elliptical galaxies, only a small fraction of the mass of NGC 4889 is in the form of stars that radiate energy. Assuming a mass to light ratio of 6.5 as with other elliptical galaxies, NGC 4889 may be a thousand times more massive than the Milky Way.

On December 5, 2011, astronomers measured the velocity dispersion of the central regions of two massive galaxies, NGC 4889, and the other being NGC 3842 in the Leo Cluster. According to the data of the study, they found out the central black hole of NGC 4889 is 5,200 times more massive than the central black hole of the Milky Way, or equivalent to 21 billion solar masses (best fit of data; possible range is from 6 billion to 37 billion solar masses). This makes it one of the most massive black holes on record. The diameter of the black hole's immense event horizon is about 20 to 124 billion kilometers, 2 to 12 times the diameter of Pluto's orbit. The ionized medium detected around the black hole suggests that NGC 4889 may have been a quasar in the past. It is quiescent, presumably because it has already absorbed all readily available matter.

Giant elliptical galaxies like NGC 4889 are believed to be the result of multiple mergers of smaller galaxies. There is now little dust remaining to form the diffuse nebulae where new stars are created, so the stellar population is dominated by old, population II stars that contain relatively low abundances of elements other than hydrogen and helium. The egg-like shape of this galaxy is maintained by random orbital motions of its member stars, in contrast to the more orderly rotational motions found in a spiral galaxy such as the Milky Way.

The space between the stars in the galaxy is filled with a diffuse interstellar medium of gas, which has been filled by the elements ejected from stars as they passed beyond the end of their main sequence lifetime. Carbon and nitrogen are being continuously supplied by intermediate mass stars as they pass through the asymptotic giant branch. The heavier elements from oxygen to iron are primarily produced by supernova explosions within the galaxy. The interstellar medium is continuously heated by the emission of in-falling gases towards its central SMBH.>>
Art Neuendorffer

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by sillyworm2 » Mon Mar 26, 2018 4:37 pm

"NGC 4889 may be a thousand times more massive than the Milky Way." Wow Thanks Neufer and Ann ,etc The info about NGC 4889 is fascinating!

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by Curiouser A. Curiouser » Mon Mar 26, 2018 4:43 pm

Ann wrote:
Mon Mar 26, 2018 2:44 pm
Whatever the exact processes, it does seem that galaxies that have long been members of massive galaxy clusters lose their ability to form new stars, and become shapeless and yellow.
Do you suppose that as the universe expands the ISM will become cooler and less dense thus allowing these giant ellipticals to restart star formation?

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by Chris Peterson » Mon Mar 26, 2018 4:50 pm

Curiouser A. Curiouser wrote:
Mon Mar 26, 2018 4:43 pm
Ann wrote:
Mon Mar 26, 2018 2:44 pm
Whatever the exact processes, it does seem that galaxies that have long been members of massive galaxy clusters lose their ability to form new stars, and become shapeless and yellow.
Do you suppose that as the universe expands the ISM will become cooler and less dense thus allowing these giant ellipticals to restart star formation?
The Universe doesn't expand within galaxy clusters, as gravity holds everything together. Ellipticals that undergo subsequent collisions can have new star formation triggered. Ultimately, I'd expect any galaxy cluster to coalesce into a single galaxy, which would probably not have much star formation occurring.
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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by Ann » Mon Mar 26, 2018 4:58 pm

Curiouser A. Curiouser wrote:
Mon Mar 26, 2018 4:43 pm
Ann wrote:
Mon Mar 26, 2018 2:44 pm
Whatever the exact processes, it does seem that galaxies that have long been members of massive galaxy clusters lose their ability to form new stars, and become shapeless and yellow.
Do you suppose that as the universe expands the ISM will become cooler and less dense thus allowing these giant ellipticals to restart star formation?
Well, it depends on how strong the "repulsive" force known as dark energy is and how it will evolve in the future, but for now we see no signs that galaxy clusters like the Coma Cluster are going to disintegrate. And for as long as dense galaxy clusters contain gas that keep falling into supermassive black holes, I don't see why the gaseous halos around galaxy clusters should cool down significantly.

It should be noted that there really are elliptical galaxies that exist in relative isolation. I can't think of any such galaxy now, because individual elliptical galaxies don't interest me that much, but I know that isolated ellipticals exist. Their gaseous halos can only be heated by these galaxies' own black holes, not by the black holes of any supermassive galactic neighbors. But I don't think that the isolated ellipticals have, generally speaking, re-started their star formation on any sort of significant level.

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by Ann » Mon Mar 26, 2018 5:26 pm

Chris Peterson wrote:
Mon Mar 26, 2018 4:50 pm

The Universe doesn't expand within galaxy clusters, as gravity holds everything together. Ellipticals that undergo subsequent collisions can have new star formation triggered. Ultimately, I'd expect any galaxy cluster to coalesce into a single galaxy, which would probably not have much star formation occurring.
The Hercules Cluster of galaxies. Photo: Bob Franke.
Source: http://bf-astro.com/abell2151.htm
Maybe, maybe we are seeing what may be new star formation in interacting galaxies that may have started out as ellipticals in the Hercules Cluster of galaxies. But the Hercules Cluster of galaxies is a special case, because it still contains many spiral galaxies. The Hercules Cluster has probably formed relatively recently.

The Perseus Cluster of galaxies.
Photo: R. Jay GaBany.

















Another galaxy cluster that appears to be at least somewhat "young" is the Perseus Cluster. Perseus A, the powerful radio galaxy, is the pinkish galaxy at about 9 o'clock in the picture. Perseus A consists of an elliptical galaxy that is in the process of colliding with a relatively small spiral galaxy, and the interaction is accompanied by star formation and red emission nebulas.

We can also see, in R Jay GaBany's picture, that there are a few other spiral galaxies (or "blue" galaxies) in the Perseus Cluster. There is one at center right, NGC 1268, an Sb type of galaxy. And there is one at top "center-left", UGC 2665.

But I believe that the collision of two elliptical galaxies will rarely produce much star formation. In the picture of the Hercules galaxy, at 8 o'clock, is a perfect example of a "dry" merger between two ellipticals. The merger makes the galaxies throw out large tidal tails of yellow stars, but we see no signs of young blue stars or large dusty nebulas which may give rise to star formation.

I believe that over time, most big galaxy clusters will be "all yellow", where all the members are elliptical or lenticular galaxies with no or almost no star formation.

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by Chris Peterson » Mon Mar 26, 2018 5:36 pm

Ann wrote:
Mon Mar 26, 2018 5:26 pm
Chris Peterson wrote:
Mon Mar 26, 2018 4:50 pm

The Universe doesn't expand within galaxy clusters, as gravity holds everything together. Ellipticals that undergo subsequent collisions can have new star formation triggered. Ultimately, I'd expect any galaxy cluster to coalesce into a single galaxy, which would probably not have much star formation occurring.
But I believe that the collision of two elliptical galaxies will rarely produce much star formation.
I make no assessment of the likelihood, only the possibility. Ellipticals tend to be calm and stable. In order to stimulate new star formation (assuming they are not depleted of hydrogen) you need to do something to mix things up and add energy to the system, and a collision is the most obvious way for that to happen.

But in the long run, assuming we have single coalesced ellipticals far enough apart that cosmological expansion overcomes gravitational attraction, collisions will cease and we'll be left with galaxies that no longer support star formation.
Chris

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by Cliff Kancler » Mon Mar 26, 2018 7:03 pm

Given that the universe is expanding, has there ever been an observation of a distant galaxy that completely disappeared? Admittedly that is a very long shot but I wonder what might be learned?

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by Chris Peterson » Mon Mar 26, 2018 7:08 pm

Cliff Kancler wrote:
Mon Mar 26, 2018 7:03 pm
Given that the universe is expanding, has there ever been an observation of a distant galaxy that completely disappeared? Admittedly that is a very long shot but I wonder what might be learned?
You mean a galaxy that we could see, and then some time later couldn't? No. We can't see that close to the edge of the visible universe (and never will be able to do so using electromagnetic radiation).
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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by Visual_Astronomer » Mon Mar 26, 2018 8:06 pm

alter-ego wrote:
Mon Mar 26, 2018 5:02 am
The first time I saw this cluster through a 6" scope left me in awe. To this day I recall that moment.
This view measures 30' across a diagonal - the image is fully contained within a full moon span.
The sight of it through my 20" is spectacular!

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by Guest » Mon Mar 26, 2018 9:55 pm

Chris Peterson wrote:
Mon Mar 26, 2018 7:08 pm
Cliff Kancler wrote:
Mon Mar 26, 2018 7:03 pm
Given that the universe is expanding, has there ever been an observation of a distant galaxy that completely disappeared? Admittedly that is a very long shot but I wonder what might be learned?
You mean a galaxy that we could see, and then some time later couldn't? No. We can't see that close to the edge of the visible universe (and never will be able to do so using electromagnetic radiation).
Logically, if there are galaxies we can see and galaxies we can't, then there is a transition region. It would seem like that region is like an "event horizon". And it's moving faster than the speed of light which may be why you phrased your answer that way. I have found some discussion on this in "Ask an astronomer", to wit: "As a consequence of their great speeds, these galaxies will likely not be visible to us forever; some of them are right now emitting their last bit of light that will ever be able to make it all the way across space and reach us (billions of years from now). After that, we will observe them to freeze and fade, never to be seen again". However that sentence refers to present time, i.e. "right now" whatever that is, whereas if the universe is old enough then there should be some galaxies well in the past whose light is their last light to us. That would seem to be right up to the edge but maybe the universe isn't old enough yet? That discussion was here. http://curious.astro.cornell.edu/about- ... termediate The penultimate paragraph seems to suggest there are some galaxies ready to blink off.

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by sillyworm2 » Mon Mar 26, 2018 10:02 pm

Getting sad thinking that one day all the Cluster's Galaxies will be boring Ellipticals. hee hee Now..are there situations where NEW Galaxies can form? Also...are there scenarios where when 2 Galaxy Cluster merge... this can spawn star formation? I believe I've read that the gas surrounding/within
this situation will be too hot for this to occur?

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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by Chris Peterson » Mon Mar 26, 2018 10:07 pm

Guest wrote:
Mon Mar 26, 2018 9:55 pm
Chris Peterson wrote:
Mon Mar 26, 2018 7:08 pm
Cliff Kancler wrote:
Mon Mar 26, 2018 7:03 pm
Given that the universe is expanding, has there ever been an observation of a distant galaxy that completely disappeared? Admittedly that is a very long shot but I wonder what might be learned?
You mean a galaxy that we could see, and then some time later couldn't? No. We can't see that close to the edge of the visible universe (and never will be able to do so using electromagnetic radiation).
Logically, if there are galaxies we can see and galaxies we can't, then there is a transition region. It would seem like that region is like an "event horizon". And it's moving faster than the speed of light which may be why you phrased your answer that way. I have found some discussion on this in "Ask an astronomer", to wit: "As a consequence of their great speeds, these galaxies will likely not be visible to us forever; some of them are right now emitting their last bit of light that will ever be able to make it all the way across space and reach us (billions of years from now). After that, we will observe them to freeze and fade, never to be seen again". However that sentence refers to present time, i.e. "right now" whatever that is, whereas if the universe is old enough then there should be some galaxies well in the past whose light is their last light to us. That would seem to be right up to the edge but maybe the universe isn't old enough yet? That discussion was here. http://curious.astro.cornell.edu/about- ... termediate The penultimate paragraph seems to suggest there are some galaxies ready to blink off.
As far as we understand, the vast majority of the galaxy is moving away from us at faster than c, that is, lies beyond the horizon that defines the visible universe (a sphere around us which is 46 billion light years away, or 13.7 billion years light travel time). As we approach that horizon with our instruments, we reach back to the Big Bang itself, and a period where there were no galaxies yet. Further limiting our efforts, there was a period of several hundred thousand years after the BB when the Universe was opaque to electromagnetic radiation. We'll never see that using light. Perhaps gravitational waves will allow us to make measurements of that very early period.
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Re: APOD: The Coma Cluster of Galaxies (2018 Mar 26)

Post by Chris Peterson » Mon Mar 26, 2018 10:08 pm

sillyworm2 wrote:
Mon Mar 26, 2018 10:02 pm
Getting sad thinking that one day all the Cluster's Galaxies will be boring Ellipticals. hee hee Now..are there situations where NEW Galaxies can form? Also...are there scenarios where when 2 Galaxy Cluster merge... this can spawn star formation? I believe I've read that the gas surrounding/within
this situation will be too hot for this to occur?
I don't believe there is any evidence that the Universe is currently capable of creating new galaxies. That was something that happened during the first few hundred million years.
Chris

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