"Cut from different cloth" (www.physorg.com/news82127598.html) 07 Nov. 2006  

 The article ` Cut from different cloth' is on many sites and tells how the Milky Way is
 surrounded by small dim `dwarf' galaxies (at about a quarter of the distance to Andromeda
 our nearest galactic neighbour). These `dwarf' types were thought to have contributed to
 the build-up of large galaxies like the Milky Way.

 But - the scientists divide stars roughly into two types: `new' stars which are made of
 hydrogen and helium, and `old' stars which, continuing their internal nuclear processes,
 are making heavier elements. [Heavier elements are called `metals' by the astronomers,
 even though many are familiar to us in gaseous compounds, like carbon for instance.]   

 So, if these small galaxies build into bigger galaxies, you'd expect to see both new and
 older stars in them, but probably more of the new ones - of hydrogen and helium.

 And there's the problem - what they've found is just the opposite. The stars in the four
 dwarf galaxies examined are actually quite rich in Iron - formed much later on in a
 star's nuclear life-time.

 [On the PhysOrg page there's four graphs of the Iron content of the respective galaxies
 Fornax, Sextans, Sculptor and Carina. You can see a cut-off to the left, so no stars
 with very low Iron content.]

 So, if you had to guess why, we could simply say "It's a one-off situation - those small
 galaxies did have `new' stars but they've all gone into older types."  That just says
 there's no new star building (of the sort going on within the Milky Way), happening
 in theose `dwarfs'.  But, worse, it also implies we are looking at a special time - a
 thing scientists don't like to assume nowadays (they've allowed too many mistakes like
 that in the past).

 OK, take another guess.  Let's say, because we see no `new' stars in the dwarfs, there
 never were any!  In that case the dwarfs are maybe only `catcher' galaxies, holding the
 stars which were born elsewhere (maybe within the Milky Way) and flung outside by some
 gravitational sling-shot accidents, which must happen from time to time.  And that the
 process between `sling-shot' and `catching' takes a long time, so any `new' stars flung
 out simply can't make it to the `catcher' galaxies!

 That might explain why we see only metal-rich stars in those dwarf galaxies surrounding
 the Milky Way.  And why those galaxies are so dim.  We see most brightness around the
 areas, often in a large galaxy like the Milky Way, where dust clouds and gasses are being
 shocked, compressed and swirled around by gravitational forces, to form the disks of
 new stars and `solar systems'.

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