Stars outside galaxies

[pmrid]

Here is the question that demonstrates my ignorance. Well, so be it. The known cosmos is said to contain 100 billion galaxies each with hundreds of billions of stars whirling around within their separate gravitational systems. Between the galaxies, dark matter, perhaps, stray gas clouds like Smith's Cloud, but what about stars? Are there stars either sole or in small clusters in the void between galaxies? Or do stars only form and remain within galaxies?

Peter

[el_draco]

I reckon there would have to be the odd star out there but I doubt you would find clusters. Whether the individuals are actually free from the galaxy is another matter and finding them harder still. There is a halo of stars around the galaxy but actually being an escapee, dont know, big escape velocity would be required I suspect.

However, stars in very ecentric orbits.. should be common enough... bloody lonely place to be though. Then again, imagine the veiw from a few thousand light years above the galactic plane.... come to pappa! :thumbsup:

[michaellxv]

Some models of galaxy collisions show stars being flung out of the system. I don't see how a star could form now from an isolated gas cloud, there would be nothing to trigger to process.

In the very young universe before galaxies there must have been stars forming essentialy on their own just to get things going.

[mswhin63]

It would seem logical for this approach, larger stars that form inside the galaxy towards the outer edge might be too large for the gravity v cetrifical force to keep it in for long.

Curious if this is correct would it be possible to match a star with it's galaxy like matching our own continental drift.

[GrampianStars]

here ya go Peter
intergalactic stars :thumbsup:
http://hubblesite.org/newscenter/archive/releases/1997/02

http://kencroswell.com/VirgoIntergalactic.html

http://www.earthsky.org/interviewpost/space/intergalactic-stars-provide-clue-to-own-origin

http:// .gsfc.nasa.gov/docs/StarChild/questions/question29.html (http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question29.html)

[pmrid]

Thanks Rob.
Interestingly, the orphans discovered in the Virgo group were all red giants (i.e. highly luninous) so it would probably follow that there were actually a hell of a lot red dwarfs and other orphans out there of lower luminosity, mirroring the same proportions as in the galaxy.
I was thinking in my uninformed way about the missing matter, the so-called 'dark matter' and wondering why the intergalactic spaces were thought of as veing largely voids. In all probability, there is a massive amount of stellar mass out there just hangin' around, unseen, uncounted.
Peter

[AlexN]

As was mentioned, during galactic collisions, stars can go flying ever which way.. I would assume, depending on velocity and eccentricity of a stars orbit around the core of a large galaxy, I wouldn't say escapees are impossible.. Unlikely perhaps, but not impossible..

The chances of clusters would be significantly lower, as stars flung out by separate galaxies are heading out into a seemingly infinitely large, four dimensional area, their own gravity would only extend so far, and the chances of their individual gravitational influence coming close enough, and being strong enough to bring them together, and slow their velocity down to a point where they would come back at each other and form a cluster, or binary system is very low... Lets also bring into play the fourth dimension. Time.

Two similarly sized stars (S1 and S2) are spat out of two galaxies (G1 and G2) that are 100,000 Ly apart. They are traveling at a ridiculously high velocity of 0.5ly on an intersecting path with each other, but the point of intersection is 20,000 ly from G1, and 84,000 ly from G2 (keep in mind, I know, 20k ly + 85k ly = 105k ly - Space is a 3 dimensional area) The star from G1 is going to reach the point of intersection in 40,000 years. where as the star from G2 will reach that same point in space in 170,000 years, assuming of course that there is no other gravitational input from any other body. There would however be gravitational input on S1 and S2 from their former parent galaxy, their acceleration would slow as a result of this... so the time frames would not be as I mentioned earlier, however their rate of deceleration would be somewhat the same (proportional to the size of the galaxy that they were escaping)

The chances that two stars would be sent out into the void from two galaxies would meet somewhere in between and form a gravitationally bound cluster or binary pair, in my opinion, would be insanely low.. There would be more chance that S1 and S2 would eventually find a new home in another galaxy, as the influence of a body like a galaxy out in the void is a lot stronger than that of a single star hurtling across space..

If we were talking about some mythical super-massive neutron stars, both with a mass like 50x10^2 solar masses, the chances would be higher, but still not significant enough to warrant conversation I don't believe.

[pmrid]

The point about the links Rob posted was that in an insanely small and seemiingly empty bit of the sky in Virgo, these guys found 350 red giants that were orphans. The ration of red dwarfs to 'others' in our galaxy is about 2:1. Assuming those orphans were the by-product of a galactic collision/stripping/whatever the likely proportions of stars stripped and flung out into the void wouldn't differ all that much. So there is probably a much bigger population of stars out there, too small and too dim to be seen individually.

So AlexN, while you say escapes are not impossible but unlikely, it would seem that a small patch of empty sky in Virgo says you're wrong. These orphans, it is said are beyond the gravitational reach of their progenitor galaxies, but are probably within that of the galaxy cluster in which they move.

As for B1 and B2, ....

Peter

[AlexN]

Yeah, so not impossible, but still, unlikely... Its unlikely that you will win the lotto, but every week, somebody does...

In a close cluster of galaxies, there are going to be collisions which will no doubt send stars out of the reach of their progenitor galaxy... And in a large cluster of galaxies, this will happen "Often". How many stars get sent out astray when two galaxies collide? I would say definitely more than one... The combined gravitational influence of a galaxy cluster will hold them "near by" (in intergalactic terms)...

My comments regarding how likely it is were more based on the fact that there are roughly 10^11 ~ 10^12 stars in our galaxy, and perhaps 10^11 ~ 10^12 galaxies in the universe. Using these somewhat arbitrary, although according to ESO, somewhat accurate numbers, there are roughly 10^22 ~ 10^24 (1,000,000,000,000,000,000,000,000) stars in the universe... There would need to be a hell of a lot of intergalactic stars for it to be considered statistically significant... and a hell of a lot more than that for it to be considered "common"

Do stars that are still bound to their parent galaxy cluster's gravitational influence still count as intergalactic stars? They may not be in a galaxy, but a group of galaxies still controls its velocity and location, I would assume that the stars orbit around the cluster will eventually decay, and it will once again become a part of one of the galaxies within the cluster.. Perhaps not before another collision within the cluster sends more orphans out..

My thoughts are that a true intergalactic star, not under the gravitational influence of any galaxy and or galaxy cluster would be a rarity... In my uninformed opinion anyway..

[pmrid]

Since I have long since exhausted by skills in cosmology, I am left, as a layperson, to reflect on the possibility that out there in the intergalactic ether, orbiting around a little G2 class star with a little air and a little water, is a bug making it's way through a heavily irradiated and therefore short existence. In keeping with the tenor of this discussion, we will call him/her Bug 1 (B1 for short).
B1 lives under a rock on the surface of this watery/rocky planet out there in the middle of the spaces between the Virgo Supercluster of Galaxies. When he steps out of the shade of his rock for a whiz and a look 'round the neighbourhood, he has a close-up and personal look at the sky and just before B2, a larger and hungrier bug reduces him to gnat droppings, his last sight is of M84 and M86 each larger than our moon. Whoa. What a ride.
Peter