Are there "single" stars?

[Stefan Haertel]

I saw a (stunningly beautiful) picture of two galaxies today, which are in the process of uniting. In the background, there were a couple of stars, some bright and some less bright. I suppose these are all galaxies themselves, but I still wonder, are there single stars/suns which aren't part of any galaxy? Does anybody know?

 

[The Last Conformist]

There are stars that have been ripped out of galaxies by tidal forces, often forming bands or lose clusters of such "exile" stars.

As far as I know, there are no known stars that are of non-galactic origin.

 

[Perfection]

It's also theorized (I'm not sure to what veracity, so you can take this as anecdotal) that there are micro galalxies that have so little ordinary matter (they, like most galaxies being composed mostly of dark matter) that it's mostly just cold gas with very few stars.

 

[carlosMM]

there are a lot of stars that are parts of galaxies, but appear not to - those formed in the very early days of our galaxy, e.g., when the entire things hadn't flattened yet through rotation. Back then it was a large ball, and stars formed all over the ball. Now, thopse that are no part of the plane of rotation (the spiral shape) look a bit lonely.

 

[Pasi Nurminen]

This might be threadjacking, but could you post the picture of the two galaxies in the process of colliding, please?

 

[Stefan Haertel]

Thanks for the info so far!

EDIT: Here's the picture, but since I had to photograph it from the newspaper it was in, it's not in very good quality. It should still give an impression though.

 

[The Last Conformist]

there are a lot of stars that are parts of galaxies, but appear not to - those formed in the very early days of our galaxy, e.g., when the entire things hadn't flattened yet through rotation. Back then it was a large ball, and stars formed all over the ball. Now, thopse that are no part of the plane of rotation (the spiral shape) look a bit lonely.

An interesting example of this is Arcturus, which is currently well within the disc of the Milky Way, but whose trajectory is at a considerable angle to the plane of the disc. In some dozen million years, it will be high above (or below; can't recall) the galactic plane.

(An alternate explanation of it's trajectory is it's part of a dwarf galaxy that was cannibalized by the Milky Way.)

 

[Yom]

Can one of our resident astronomers (TLC?) explain why, in rare cases, a "single" star cannot be created? A star simply results from the condensation of a nebula, right? Why couldn't a large amount of dust and matter collect outside of a galaxy over time and eventually form a star?

 

[carlosMM]

Can one of our resident astronomers (TLC?) explain why, in rare cases, a "single" star cannot be created? A star simply results from the condensation of a nebula, right? Why couldn't a large amount of dust and matter collect outside of a galaxy over time and eventually form a star?

usually, you will get a ring of raotating material, leadin to a dual star system.

 

[LLXerxes]

as big as the universe is I'd assume so. but then again,

 

[The Last Conformist]

Can one of our resident astronomers (TLC?) explain why, in rare cases, a "single" star cannot be created? A star simply results from the condensation of a nebula, right? Why couldn't a large amount of dust and matter collect outside of a galaxy over time and eventually form a star?

No-one's saying it can't happen, but there are some grounds for thinking it should be rare.

Galaxies and clusters are the result of gravitational collapse of regions that ended up with a higher-than-average density in the aftermath of the big bang. These density variations had a characteristic scale to them; there simply wasn't any denser regions as small as a a single star (don't ask me for the details - the point is a region of deviant density had to be sufficiently big not to get smeared out by homogenizing interaction). The dense regions became denser and denser till stars started to form in the densest bits (that became galaxies), while the less dense bits lost matter to the tense bits, thus becoming even emptier and less able to sustain stellar birth.

 

[Perfection]

Why couldn't a large amount of dust and matter collect outside of a galaxy over time and eventually form a star?

Well this dust and matter has a tendancy to fall back toward the galaxy, but it is true that occasionally stars will form in these halo regions, however they are still considered part of the galaxy, just in the outermost regions.

 

[Jack the Ripper]

After the collision of two galixies, there often are, as long as thea stars arent thrown into the galactic core. I've heard that the milky way and the andromada will do this relatively soon (in cosmic terms).

 

[The Last Conformist]

In something like five billion years, yes. That's not really "soon" even in cosmological terms; the universe will then be ~40% older than it is today.

 

[Blackbird_SR-71]

Like answered before single stars exist but none have been formed outside of a galaxy.

 

[Perfection]

Like answered before single stars exist but none have been formed outside of a galaxy.

Well I wouldn't go as far to say that none have formed, I'd just suspect them to be extremely rare.

 

[Blackbird_SR-71]

Perfection-

Yeah i guess but your right they are extremely rare.