Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Refractor on 06/05/2010 14:30:02

Title: Do stars exist only in galaxies?
Post by: Refractor on 06/05/2010 14:30:02

Geoff asked the Naked Scientists:
   
Do all stars exist in galaxies or are there some loners out by themselves in the space in between?

Thanks for the great podcast (http://www.thenakedscientists.com/HTML/podcasts/).

What do you think?

Title: Do stars exist only in galaxies?
Post by: LeeE on 06/05/2010 17:00:09

Stars can only form in galaxies but it is possible for a relatively small star to be ejected from its parent galaxy as a result of a close encounter with a much larger star in a slingshot maneuver.

Title: Do stars exist only in galaxies?
Post by: Refractor on 09/05/2010 10:05:02

OK, so presumably they'd be not far from the galaxy of their birth.  I wonder if there are any known examples of stars out on their own, and how far out they might be.

Title: Do stars exist only in galaxies?
Post by: GlentoranMark on 09/05/2010 11:06:36

I've never considered the question so thanks for asking.

I done a little googling and found this:

http://en.wikipedia.org/wiki/Category:Extragalactic_stars

I also notice that one of the shuttle missions was used to research such stars.

Title: Do stars exist only in galaxies?
Post by: LeeE on 09/05/2010 14:09:49

Quote from: GlentoranMark on 09/05/2010 11:06:36

I've never considered the question so thanks for asking.

I done a little googling and found this:

http://en.wikipedia.org/wiki/Category:Extragalactic_stars

I also notice that one of the shuttle missions was used to research such stars.

Actually, most of the stars in that list are only extra-galactic in the sense that they exist outside our galaxy; apart from HE 0437-5439 and PSR J0537-6910, they are all in the Large Magellanic Cloud (LMC).

Only the first star in that list, HE 0437-5439, is clearly outside any galaxy, having been ejected from the LMC.

It's less clear whether PSR J0537-6910 is actually outside the LMC or still within it.  Its Right ascension and Declination put it in the direction of the LMC but it seems to be 13,000 light years further away from us than the LMC itself.  However, the LMC is reckoned to be ~14,000 light years across, so if the same measuring datum are used for both the LMC and PSR J0537-6910 then PSR J0537-6910 may only be ~6,000 light years outside the LMC.

What I'm not sure about is whether the same datum do apply though.  It wouldn't surprise me to find that the distance between the LMC and our Milky Way galaxy is measured between the galactic centers, so while the center of the LMC may ~157,000 light years from the center of our Milky Way galaxy, the Earth is ~25,000 light years from the center of the Milky Way galaxy.  If then, the distance to PSR J0537-6910 is measured from the Earth, as seems likely to me, but the distance to the LMC is measured from the center of the Milky Way, PSR J0537-6910 could be well within the LMC.