View Full Version : Discussion: Star Clusters Could Be Galaxy ...

2004-Aug-13, 04:41 PM
SUMMARY: Globular star clusters - groupings of millions stars in close formation - are some of the most beautiful objects in the sky. Our own Milky Way has about 200 of them, but astronomers believe we used to have many more. Astronomers think that these star clusters might actually be all that remains from irregular dwarf galaxies were consumed by the Milky Way and had their outer stars stripped away. A team from Harvard and the Carnegie Institute of Washington observed 14 globular clusters in a distant galaxy, and realized that they're so large, they nearly overlap the size of small galaxies, and have many similar characteristics.

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2004-Aug-14, 02:49 PM
very good info

2004-Aug-19, 09:55 AM
very useful info.a wonderful image.

2005-Jul-21, 09:22 AM

2005-Jul-21, 09:22 AM

2005-Jul-22, 12:51 AM
That particular evolutionary scheme has been around since the 1940's, with varying degrees of support. A Dwarf Irregular (dIrr) might evolve into a Dwarf Elliptical or Dwarf Spheroid (dE or dSph), pretty much on its own. Tidal interactions with the much more massive host galaxy cause both the diffusion of the dwarf's envelope and the densification of its nucleus, forming a Nucleated Dwarf Elliptical (dE,N) such as M110. Further stripping by the host removes the envelope entirely, but densifies the nucleus still further, causing late star-formation activity -- the new object is a Bright Compact Dwarf (BCD), such as M32, and may or may not harbor a late-blooming Black Hole (M32 does).

The next logical step would be further compactification and stripping, resulting in an object closely resembling a globular cluster. All of these evolutionary steps are sensitively dependent on the ratio of the host galaxy's mass to that of the dwarf, and to the particular orbit assumed by the dwarf.

It is fair to say that some of the objects that look like globular clusters are beat-up galaxies. There are several good examples in the Palomar catalog, like Palomar 5.

Based on current location, most globulars have halo orbits, which may or may not cross the disc/spheroid of the parent galaxy. Of course, they spend most of their (low-velocity) time near apoapsis. We might suspect that satellites in orbits aligned with the disk get sucked into it, like the Canis Major Dwarf and the (probably related) Monoceros stream.

The two most recently discovered MW dwarf satellites actually overlap the globular population in central density, luminosity, and orbital distance-- there is some discussion as to what to call them. See:



Enjoy! S

2005-Jul-26, 09:49 PM
Great links Steve!

So many interesting things still being found in our 'backyard'!!

Oh to be given 100 hours or so of prime observing time on an OWL or ELT!!!

Does anyone have a link to the original UT story?