Exogalactic starsystems

[Cyperium]

Isn't it possible, that there are small systems of stars between the galaxies?

All the stars we see in the sky are inside our own galaxy (or are in fact a galaxy/planet/satellite). Everything we see that is beyond our galaxy are other galaxies. Cause at that distance the stars would give out too little light to be noticed. What we see is instead the system of billions of stars that are contained in a galaxy.

However, the space between the galaxies might be filled with lonely stars, perhaps systems of only hundred stars or so. Perhaps even stars/systems ejected from galaxies.

I know it's only speculation, but it could be so, yes?

I have a question, how many average stars would have to be in a system in order for it to be visible outside of our galaxy?

And a obvious question, could a single star outside of any system ever be noticed outside the galaxy?


Perhaps inhabitants of that star looks at a galaxy and think about how lonely they are...it might be a privilege to be in the milky way.

 

[kaneda]

I seem to remember a few years ago that they had found lone stars outside our galaxy. They get too close to the edge of the rim and drift away. We have detected stars passing through the plane of our galaxy. It isn't all clean cut galaxies. Check out the pictures :


http://en.wikipedia.org/wiki/Local_Group


Local Group - Wikipedia, the free encyclopedia

 

[Pandaemoni]

There are stars outside of galaxies. It's not that they drift away, it's that they are flung off. In order to escape a galxy's gravitation, a star needs to hit an escape velocity.

 

[Xylene]

Suppose there's a supernova in one of the spiral arms of any galaxy, near the outer edge of the arm. The shockwave from the supernova would spread out 360 degrees, in all directions. As the shockwave passes back through the thickness of the arm, it encounters clouds of gas, which may be compressed enough to begin the formation process for the birth of new stars. So it'll also occur as the shockwave travels out into deeper space, beyond the galactic edge. Any gas and dust cloud out there may also be compressed enough to form stars eventually. That could be one way for exogalactic star systems to be created.

You can also have rogue planets wandering about, both within and outside galaxies. Apart from absorbing or annihilating those worlds that are closest to it, a supernova will blast off the atmospheres of even the remote planets in its solar system. Having dispersed its energy, the star shrinks to a white dwarf or Neutron star. However, the initial surge of gases from the supernova may have been strong enough to expel some of the outermost planets from the system entirely, so that they now drift off and become rogue worlds. It could be that these vagrants are captured by other systems, but if not, they continue drifting.

Also, giant planets within any solar system can act together to throw smaller planets right out of the system altogether, so that they also become drifters. Such wanderers are attracted to any larger, heavier body, and may end up as the captured moon of a giant planet, or (all going well) end up inorbit around another star.

 

[Cyperium]

Thank you for your replies.

The question remains though; could we spot a single star outside of our galaxy? How much light would it have to give out, assuming that it is at a certain distance from our galaxy, in order for it to be seen by us?

Also, how large a collection of average stars would have to be in order for us to spot them outside of our galaxy?

 

[Fraggle Rocker]

The question remains though; could we spot a single star outside of our galaxy? How much light would it have to give out, assuming that it is at a certain distance from our galaxy, in order for it to be seen by us? Also, how large a collection of average stars would have to be in order for us to spot them outside of our galaxy?

I suspect that the answers to your questions will change steadily as we develop more sensitive instruments. The existence of other galaxies was only a hypothesis unsupported by observational evidence until the 20th century. Proof of the existence of other planetary systems was only acquired in the last few decades, and we still haven't found a planet with the right conditions to evolve a biosphere even remotely similar to our own.

 

[Cyperium]

I suspect that the answers to your questions will change steadily as we develop more sensitive instruments. The existence of other galaxies was only a hypothesis unsupported by observational evidence until the 20th century. Proof of the existence of other planetary systems was only acquired in the last few decades, and we still haven't found a planet with the right conditions to evolve a biosphere even remotely similar to our own.

Ok, I guess that's fair enough thanks.

 

[jmpet]

Isn't it possible, that there are small systems of stars between the galaxies?

Yes.

However, the space between the galaxies might be filled with lonely stars, perhaps systems of only hundred stars or so. Perhaps even stars/systems ejected from galaxies. I know it's only speculation, but it could be so, yes?

Sure- why the hell not?

I have a question, how many average stars would have to be in a system in order for it to be visible outside of our galaxy?

It's all relative.

And a obvious question, could a single star outside of any system ever be noticed outside the galaxy?

It's also relative.

---

Star systems outside of a galaxy- as infrequent as they are- rarely evolve to class M planets. Instead of being bound by the tensor field of our galaxy they are lost in a sea of dark matter and energy. Goldilocks ain't here.

 

[Cyperium]

Yes.



Sure- why the hell not?



It's all relative.



It's also relative.

---

Star systems outside of a galaxy- as infrequent as they are- rarely evolve to class M planets. Instead of being bound by the tensor field of our galaxy they are lost in a sea of dark matter and energy. Goldilocks ain't here.

We seldom think about what is between the galaxies, as the distances in that scale are so enormous.

Are there defined laws for that scale? (spiral galaxy formation etc.)

What are those laws?

Are there also laws for the scale of galaxy clusters?

 

[Xylene]

According to the Guinness Book of Records (who should know) the largest nebulae or galaxies are about 200,000 light years across, so there does seem to be a definite upper limit. Personally, I can't see why--I would've thought that there was no limit, that things could just go on coalescing. There are definitely different types of galaxies, which all have different paths of physical evolution.

 

[Fraggle Rocker]

According to the Guinness Book of Records (who should know) the largest nebulae or galaxies are about 200,000 light years across, so there does seem to be a definite upper limit. Personally, I can't see why--I would've thought that there was no limit, that things could just go on coalescing.

You're probably right, and galaxies will continue to coalesce. Isn't ours due to merge with one that's moving toward us in a few billion years?

You have to allow time for all this to happen. The biggest galaxies currently in existence are merely the ones that have formed to date.

 

[Xylene]

Andromeda and our galaxy will collide in a few billion years time, yes--I think about 6 billion years from now IIRR.

 

[Cyperium]

You're probably right, and galaxies will continue to coalesce. Isn't ours due to merge with one that's moving toward us in a few billion years?

You have to allow time for all this to happen. The biggest galaxies currently in existence are merely the ones that have formed to date.

At what scale do the galaxies move away from us (and all other galaxies)?

I was thinking that there might be a reason for the upper limit of galaxy size.

 

[Starthane Xyzth]

At what scale do the galaxies move away from us (and all other galaxies)?

Generally beyond the supercluster scale. Our Local Group is falling towards the Virgo Cluster, but remoter groups, like the Coma Cluster, are receding from us.

I was thinking that there might be a reason for the upper limit of galaxy size.

Probably the ultimate limit is set by the size of initial density fluctuations in the infant Universe after the Big Bang. While the Universe as a whole expanded, those denser pockets remained gravitationally bound and formed galaxies.

Andromeda and our galaxy will collide in a few billion years time, yes--I think about 6 billion years from now IIRR.

Galactic mergers should continue over the next trillion years or so, until present-day clusters of galaxies settle in single mega-galaxies. These, in turn, may ultimately coalesce if they were parts of a supercluster; I should think that all their constituent stars would have burned out long before that.

On the original question:

Stellar outcasts definitely exist between galaxies. They have actually been spotted in the large clusters; if not bound to a single galaxy, they can almost certainly drift out of the cluster as well. Stars are thrown out after being slingshotted to higher velocities by a more massive object, as in this case.

Whole globular clusters can also be expelled. Being composed of hundreds of thousands of stars, they are relatively easy to see in the intergalactic gulf; but as Cyperium said, a single star - especially a low-luminosity red or orange dwarf, which make up the vast majority of stars - would be quite undetectable at such distances. There may be a lot more out there than we think...

If ejected from their galaxies after forming a planetary system, they might retain at least some of their planets. Imagine a civilisation evolving in such a system. You'd have to feel sorry for them, being forever denied a starry sky.

It's also possible that the very earliest stars formed before the galaxies, when the Universe was only a million years old or so. If any of those were considerably less massive than the Sun (some believe they must all have been very large & short-lived), they are probably still shining out there somewhere. Such stars would be truly unique, in that they never have been part of any galaxy.

Star systems outside of a galaxy- as infrequent as they are- rarely evolve to class M planets. Instead of being bound by the tensor field of our galaxy they are lost in a sea of dark matter and energy.

What do you mean by tensor field? Are you implying that planets cannot form at all beyond the galactic environment? [BTW: "class M planets" is Star Trek jargon, not a real planetary science term. You mean Earthlike planets, of course.]

 

[Cyperium]

Generally beyond the supercluster scale. Our Local Group is falling towards the Virgo Cluster, but remoter groups, like the Coma Cluster, are receding from us.

Ok, thank you for the information.

Probably the ultimate limit is set by the size of initial density fluctuations in the infant Universe after the Big Bang. While the Universe as a whole expanded, those denser pockets remained gravitationally bound and formed galaxies.

My little idea that I had, was that gravity didn't just "settle" like a ball on a sheet. But that in the area beyond the "imprint" of the ball gravity bends space upwards instead, forming large-scale gravity waves. The ball in this case is the cluster of galaxies. But single galaxies should also display a similar phenomena, though with less effect.

As such the area a bit beyond (over the crust of the wave) the cluster works anti-gravitationally (as it would be a uphill for anything to get there).

An idea/sidenote; perhaps gravity is like density of space so that kinetic energy fills slower or faster independent on the mass of the object. It's harder to go uphill, not because there is a uphill or downhill but because the density of space makes it harder/or easier to carry the kinetic energy (thus the effect of downhill/uphill because of relativity, not that it falls or rises). There would be a overall "uphill" (positive spacetimedensity) from any cluster as it never settles completely.

In my idea, matter is "diluting" spacetime, so that spacetime is less dense (negative spacetimedensity) where matter is. Perhaps where matter still has influence around a object. It "takes up" spacetime so to say. What causes there would be for the positive spacetimedensity beyond the negative I don't know. Perhaps a fluctuation.

Of course, the effect of this uphill beyond the downhill is too small to be observed by our sun or planets, not because I have any reason for that, but because they haven't been observed (as far as I know).

If it could be observed it should be a small resistance before entering the the "gravity system" but too small to avoid being pulled in by the gravity. However at the scale of galaxy clusters the effect could be such that it just doesn't make it there (too steep hill before the downhill) and it might limit the size of galaxies as only those with enough speed would come in, and only the right speed to avoid being shoot out again.

On the original question:

Stellar outcasts definitely exist between galaxies. They have actually been spotted in the large clusters; if not bound to a single galaxy, they can almost certainly drift out of the cluster as well. Stars are thrown out after being slingshotted to higher velocities by a more massive object, as in this case.

Whole globular clusters can also be expelled. Being composed of hundreds of thousands of stars, they are relatively easy to see in the intergalactic gulf; but as Cyperium said, a single star - especially a low-luminosity red or orange dwarf, which make up the vast majority of stars - would be quite undetectable at such distances. There may be a lot more out there than we think...

If ejected from their galaxies after forming a planetary system, they might retain at least some of their planets. Imagine a civilisation evolving in such a system. You'd have to feel sorry for them, being forever denied a starry sky.

Yeah, I agree...

It's also possible that the very earliest stars formed before the galaxies, when the Universe was only a million years old or so. If any of those were considerably less massive than the Sun (some believe they must all have been very large & short-lived), they are probably still shining out there somewhere. Such stars would be truly unique, in that they never have been part of any galaxy.

True, I suspect many of them have been transformed into "gigantic" black holes.

What do you mean by tensor field? Are you implying that planets cannot form at all beyond the galactic environment? [BTW: "class M planets" is Star Trek jargon, not a real planetary science term. You mean Earthlike planets, of course.]

Sorry, you must have quoted wrongly. Somebody else wrote that thanks anyway! Also; thank you for your useful information.

 

[Xylene]

On the original question:

It's also possible that the very earliest stars formed before the galaxies, when the Universe was only a million years old or so. If any of those were considerably less massive than the Sun (some believe they must all have been very large & short-lived), they are probably still shining out there somewhere. Such stars would be truly unique, in that they never have been part of any galaxy.

I would say it was essential that the earliest stars formed before the galaxies--the chicken can't exist without the egg--there have to be stars for there to be galaxies, after all.

Regarding the original question, another way for stars to be spread through deep, extra-galactic space is to have a colision between galaxies; which is going to happen between our home galaxy and that of Andromeda in about 6 billion years. As the two star-systems get within a certain distance of each other, the outermost edges of the arms that approach closest will start to stretch out to make contact under the influence of their mutual gravitation. Gradually the two galaxies will merge, but it will take millions of years for this to occur--sort of watching a slow-motion train wreck.

As in the example, there'll be bits of both galaxies being flung off in all directions due to the impact. Many if not most of the star-groups that are shucked off will be eventually brought back into the newly merged galaxy by the pull of gravity; however, there will be a significant amount of stars--possibly numbering in the millions--which will be cast off into the dark so far that they are never regained. These ishmaelite stars will wander until they are captured by other galaxies.

 

[Cyperium]

I would say it was essential that the earliest stars formed before the galaxies--the chicken can't exist without the egg--there have to be stars for there to be galaxies, after all.

Regarding the original question, another way for stars to be spread through deep, extra-galactic space is to have a colision between galaxies; which is going to happen between our home galaxy and that of Andromeda in about 6 billion years. As the two star-systems get within a certain distance of each other, the outermost edges of the arms that approach closest will start to stretch out to make contact under the influence of their mutual gravitation. Gradually the two galaxies will merge, but it will take millions of years for this to occur--sort of watching a slow-motion train wreck.

As in the example, there'll be bits of both galaxies being flung off in all directions due to the impact. Many if not most of the star-groups that are shucked off will be eventually brought back into the newly merged galaxy by the pull of gravity; however, there will be a significant amount of stars--possibly numbering in the millions--which will be cast off into the dark so far that they are never regained. These ishmaelite stars will wander until they are captured by other galaxies.

Yeah, that seems reasonable. So there might be innumerable stars between the galaxies that perhaps is too far from each other to create a galaxy or have velocities that is of such nature that it can't be caught in the galaxies gravitation. This implies (to me) that the speed of the stars in each galaxy must have been pretty uniform. Perhaps the stars with the same relative speed was the ones that formed a particular galaxy? That each galaxy has the same relative speed as the stars that once formed it had. I guess it also depends on numerous other things though.

 

[Xylene]

It seems to me that in the example I gave, of two galaxies colliding (which must have happened any number of times in the 14 billion years since the Universe began) that stars would gain a tremendous velocity as they were flung here and there in space by the colossal, competing gravitation pull between the galaxies. So it wouldn't really matter what their initial velocities were, because they could be altered so easily by the gigantic forces acting upon them during the event.

 

[Repo Man]

It seems to me that in the example I gave, of two galaxies colliding (which must have happened any number of times in the 14 billion years since the Universe began) that stars would gain a tremendous velocity as they were flung here and there in space by the colossal, competing gravitation pull between the galaxies. So it wouldn't really matter what their initial velocities were, because they could be altered so easily by the gigantic forces acting upon them during the event.

Here are some animations of galactic collisions, http://burro.cwru.edu/SSAnims/

 

[Cyperium]

It seems to me that in the example I gave, of two galaxies colliding (which must have happened any number of times in the 14 billion years since the Universe began) that stars would gain a tremendous velocity as they were flung here and there in space by the colossal, competing gravitation pull between the galaxies. So it wouldn't really matter what their initial velocities were, because they could be altered so easily by the gigantic forces acting upon them during the event.

Yes, what I was thinking is that even if those are flung in a great velocity, those stars with the same velocity would eventually attract each other as they are in the same reference frame (it would be as if they stood still to each other).

I was also thinking that in the beginning, before the galaxies the stars might have different velocities and that the stars with the same velocity relative to each other would eventually form a galaxy (which would then also have that velocity in respect to other stars and galaxies).

Of course there would still be stars with exotic velocities that did not belong to any reference frame, or which is just too far from the other stars of their reference frame.