Extra-Galactic Stars: Are There Any?

[wolram]

Are the any? i would think that of all the stars in the u that a few some how
broke free from gravity and the expansion of space time has separated them from their birth galaxy.

 

[DaveC426913]

The expansion of the universe is very weak - far too weak to overcome gravity within a galaxy. It only has an effect on the gaps between galaxies.

That being said, I'm sure there are lots of intergalactic stars. Every galactic collision and even near misses within galaxies would send stars flying across the emptiness.

 

[neutrino]

As Dave said, there are stars which have been kicked out from our galaxy, and I remember reading about one form the LMC.

Here are two examples -
http://www.universetoday.com/am/publish/milkyway_exile.html?2612006
http://www.eso.org/outreach/press-rel/pr-2005/pr-27-05_p2.html
and here's a story about a pulsar fleeing at a speed of 1000km/s
http://www.nrao.edu/pr/2005/fastpulsar/

 

[wolram]

Is this ejection some what akin to a flywheel effect?

 

[Labguy]

Probably not. The last link above mentions asymmetric SN explosions but concludes that there is not enough energy to account for that velocity. What it doesn't mention is the possibility of the Neutron Star being one of a binary system where the other star goes SN. That would give more of a radial kick than an asymmetric explosion.

 

[Nereid]

It partly depends, as it always does, no your definition (of 'extragalactic star#), but there are a very great many that have been observed.

Leaving aside stars in globular clusters (they aren't 'galaxies', but I somehow feel they don't qualify, under whatever definition wolfram ends up using), there are all those in the various streams which researchers using SDSS data have found - those stripped from globular clusters and satellite galaxies, the streams which appear to have no parents, and the thousands of just plain old stars that are out there, beyond the usual boundary of the Milky Way.

Then there are the thousands in the Virgo cluster ... IIRC, the first of these was discovered a decade or more ago, and recently the HST imaged a small region, discovering lots more.

There was also, recently, a deep image of the Virgo core, showing streams and the faint glow of lots and lots of 'extragalactic stars'.

Some researchers have tried to use 'field' planetary nebulae, as tracers of the outer reaches of some galaxies, to better estimate the distribution of DM (wolfram may not count these as 'extragalactic').

Finally, in almost any image of interacting galaxies, esp those with nice long 'tidal tails', there are great numbers of stars that are well on their way to becoming 'extragalactic'!

 

[wolram]

I have just read that some or most of these extragalactic things are variables, if so why ?

 

[Nereid]

They're not; or, they're not more variable than ordinary stars of similar kinds (you may have stumbled into one of those selection effects which are the bane of astronomers' lives).

 

[wolram]

They're not; or, they're not more variable than ordinary stars of similar kinds (you may have stumbled into one of those selection effects which are the bane of astronomers' lives).

love and best wishes to nereid, many thanks.